I have just noticed that if I have 2 tag helpers targeting the same element, both can be executed. The order in which they are executed depends on the order in which they are registered in _ViewImports.cshtml.
For example, I can create another tag helper for the anchor element:
[HtmlTargetElement("a", Attributes = "foo")]
public class FooTagHelper : TagHelper
{
public override void Process(TagHelperContext context, TagHelperOutput output)
{
//Get the url from href attribute generated in the default AnchorTagHelper
var url = output.Attributes["href"].Value.ToString();
...
}
}
Use it as follows (notice I am also adding attributes of the default anchor helper like asp-controller):
<a class="menu" asp-controller="Home" asp-action="Index" foo>Foo</a>
If this helper is registered in _ViewImports.cshtml after the default ASP ones:
Whenever Process is called, the TagHelperOutput already contains the href generated by the default AnchorTagHelper. I could also update the anchor generated by the default tag helper in any way I like.
Is there any degree of control over this behavior?
You might want to decide whether or not to execute further helpers targeting the same element (As if sealing your output). You might also want to allow other helpers, but make sure some attribute wasn't modified.
Override the readonly property order, like this:
[HtmlTargetElement("a", Attributes = "foo")]
public class FooTagHelper : TagHelper
{
// This should be the last tag helper on any tag to run
public override int Order => int.MaxValue;
public override async Task ProcessAsync(TagHelperContext context,
TagHelperOutput output)
{
//...
}
}
Reading the source code of the TagHelperRunner class, I realized that the same TagHelperContext and TagHelperOutput will be shared for all the tag helpers found for the same element, which will be processed orderd by the ITagHelper.Order property.
So you can control the order in which they are executed by assigning appropriated values to the Order property. As a reference, this is the TagHaelperRunner.RunAsync method:
public async Task<TagHelperOutput> RunAsync([NotNull] TagHelperExecutionContext executionContext)
{
var tagHelperContext = new TagHelperContext(
executionContext.AllAttributes,
executionContext.Items,
executionContext.UniqueId,
executionContext.GetChildContentAsync);
var tagHelperOutput = new TagHelperOutput(
executionContext.TagName,
executionContext.HTMLAttributes)
{
SelfClosing = executionContext.SelfClosing,
};
var orderedTagHelpers = executionContext.TagHelpers.OrderBy(tagHelper => tagHelper.Order);
foreach (var tagHelper in orderedTagHelpers)
{
await tagHelper.ProcessAsync(tagHelperContext, tagHelperOutput);
}
return tagHelperOutput;
}
The default Order if you extend the class TagHelper is 0.
The MVC tag helpers like AnchorTagHelper or InputTagHelper seem to have the order defined as -1000.
So far, I have also found that you can query some of the properties in TagHelperOutput to check if a previous tag helper has modified the output. Although you cannot know if a tag helper with higher order (executed after yours) modifies the output:
TagHelperOutput.IsContentModified will return true only when the Content is modified (Not when the attributes or the PreElement, PreContent, PostElement, PostContent are modified)
TagHelperOutput.PreElement.IsModified and similar for PreContent, PostElement and PostContent will return true when those have been modified.
Content set by a previous tag helper could be removed by calling TagHelperOutput.Content.Clear() and similar for Pre/Post Element/Context properties.
Content can be completely suppressed by calling TagHelperOutput.SuppressOutput() which calls clear on every of those properties and set TagName as null. If you want the tag helper to render something you will then need to assign them again.
Finally, if you had to share some data between multiple tag helpers for the same element, you can use the TagHelperContext.Items dictionary.
Related
Is there a way to make a reflection for a view model property as an element with different name and id values on the html side.
That is the main question of what I want to achieve. So the basic introduction for the question is like:
1- I have a view model (as an example) which created for a filter operation in view side.
public class FilterViewModel
{
public string FilterParameter { get; set; }
}
2- I have a controller action which is created for GETting form values(here it is filter)
public ActionResult Index(FilterViewModel filter)
{
return View();
}
3- I have a view that a user can filter on some data and sends parameters via querystring over form submit.
#using (Html.BeginForm("Index", "Demo", FormMethod.Get))
{
#Html.LabelFor(model => model.FilterParameter)
#Html.EditorFor(model => model.FilterParameter)
<input type="submit" value="Do Filter" />
}
4- And what I want to see in rendered view output is
<form action="/Demo" method="get">
<label for="fp">FilterParameter</label>
<input id="fp" name="fp" type="text" />
<input type="submit" value="Do Filter" />
</form>
5- And as a solution I want to modify my view model like this:
public class FilterViewModel
{
[BindParameter("fp")]
[BindParameter("filter")] // this one extra alias
[BindParameter("param")] //this one extra alias
public string FilterParameter { get; set; }
}
So the basic question is about BindAttribute but the usage of complex type properties. But also if there is a built in way of doing this is much better.
Built-in pros:
1- Usage with TextBoxFor, EditorFor, LabelFor and other strongly typed view model helpers can understand and communicate better with each other.
2- Url routing support
3- No framework by desing problems :
In general, we recommend folks don’t write custom model binders
because they’re difficult to get right and they’re rarely needed. The
issue I’m discussing in this post might be one of those cases where
it’s warranted.
Link of quote
And also after some research I found these useful works:
Binding model property with different name
One step upgrade of first link
Here some informative guide
Result: But none of them give me my problems exact solution. I am looking for a strongly typed solution for this problem. Of course if you know any other way to go, please share.
Update
The underlying reasons why I want to do this are basically:
1- Everytime I want to change the html control name then I have to change PropertyName at compile time. (There is a difference Changing a property name between changing a string in code)
2- I want to hide (camouflage) real property names from end users. Most of times View Model property names same as mapped Entity Objects property names. (For developer readability reasons)
3- I don't want to remove the readability for developer. Think about lots of properties with like 2-3 character long and with mo meanings.
4- There are lots of view models written. So changing their names are going to take more time than this solution.
5- This is going to be better solution (in my POV) than others which are described in other questions until now.
Actually, there is a way to do it.
In ASP.NET binding metadata gathered by TypeDescriptor, not by reflection directly. To be more precious, AssociatedMetadataTypeTypeDescriptionProvider is used, which, in turn, simply calls TypeDescriptor.GetProvider with our model type as parameter:
public AssociatedMetadataTypeTypeDescriptionProvider(Type type)
: base(TypeDescriptor.GetProvider(type))
{
}
So, everything we need is to set our custom TypeDescriptionProvider for our model.
Let's implement our custom provider. First of all, let's define attribute for custom property name:
[AttributeUsage(AttributeTargets.Property)]
public class CustomBindingNameAttribute : Attribute
{
public CustomBindingNameAttribute(string propertyName)
{
this.PropertyName = propertyName;
}
public string PropertyName { get; private set; }
}
If you already have attribute with desired name, you can reuse it. Attribute defined above is just an example. I prefer to use JsonPropertyAttribute because in most cases I work with json and Newtonsoft's library and want to define custom name only once.
The next step is to define custom type descriptor. We will not implement whole type descriptor logic and use default implementation. Only property accessing will be overridden:
public class MyTypeDescription : CustomTypeDescriptor
{
public MyTypeDescription(ICustomTypeDescriptor parent)
: base(parent)
{
}
public override PropertyDescriptorCollection GetProperties()
{
return Wrap(base.GetProperties());
}
public override PropertyDescriptorCollection GetProperties(Attribute[] attributes)
{
return Wrap(base.GetProperties(attributes));
}
private static PropertyDescriptorCollection Wrap(PropertyDescriptorCollection src)
{
var wrapped = src.Cast<PropertyDescriptor>()
.Select(pd => (PropertyDescriptor)new MyPropertyDescriptor(pd))
.ToArray();
return new PropertyDescriptorCollection(wrapped);
}
}
Also custom property descriptor need to be implemented. Again, everything except property name will be handled by default descriptor. Note, NameHashCode for some reason is a separate property. As name changed, so it's hash code need to be changed too:
public class MyPropertyDescriptor : PropertyDescriptor
{
private readonly PropertyDescriptor _descr;
private readonly string _name;
public MyPropertyDescriptor(PropertyDescriptor descr)
: base(descr)
{
this._descr = descr;
var customBindingName = this._descr.Attributes[typeof(CustomBindingNameAttribute)] as CustomBindingNameAttribute;
this._name = customBindingName != null ? customBindingName.PropertyName : this._descr.Name;
}
public override string Name
{
get { return this._name; }
}
protected override int NameHashCode
{
get { return this.Name.GetHashCode(); }
}
public override bool CanResetValue(object component)
{
return this._descr.CanResetValue(component);
}
public override object GetValue(object component)
{
return this._descr.GetValue(component);
}
public override void ResetValue(object component)
{
this._descr.ResetValue(component);
}
public override void SetValue(object component, object value)
{
this._descr.SetValue(component, value);
}
public override bool ShouldSerializeValue(object component)
{
return this._descr.ShouldSerializeValue(component);
}
public override Type ComponentType
{
get { return this._descr.ComponentType; }
}
public override bool IsReadOnly
{
get { return this._descr.IsReadOnly; }
}
public override Type PropertyType
{
get { return this._descr.PropertyType; }
}
}
Finally, we need our custom TypeDescriptionProvider and way to bind it to our model type. By default, TypeDescriptionProviderAttribute is designed to perform that binding. But in this case we will not able to get default provider that we want to use internally. In most cases, default provider will be ReflectTypeDescriptionProvider. But this is not guaranteed and this provider is inaccessible due to it's protection level - it's internal. But we do still want to fallback to default provider.
TypeDescriptor also allow to explicitly add provider for our type via AddProvider method. That what we will use. But firstly, let's define our custom provider itself:
public class MyTypeDescriptionProvider : TypeDescriptionProvider
{
private readonly TypeDescriptionProvider _defaultProvider;
public MyTypeDescriptionProvider(TypeDescriptionProvider defaultProvider)
{
this._defaultProvider = defaultProvider;
}
public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
{
return new MyTypeDescription(this._defaultProvider.GetTypeDescriptor(objectType, instance));
}
}
The last step is to bind our provider to our model types. We can implement it in any way we want. For example, let's define some simple class, such as:
public static class TypeDescriptorsConfig
{
public static void InitializeCustomTypeDescriptorProvider()
{
// Assume, this code and all models are in one assembly
var types = Assembly.GetExecutingAssembly().GetTypes()
.Where(t => t.GetProperties().Any(p => p.IsDefined(typeof(CustomBindingNameAttribute))));
foreach (var type in types)
{
var defaultProvider = TypeDescriptor.GetProvider(type);
TypeDescriptor.AddProvider(new MyTypeDescriptionProvider(defaultProvider), type);
}
}
}
And either invoke that code via web activation:
[assembly: PreApplicationStartMethod(typeof(TypeDescriptorsConfig), "InitializeCustomTypeDescriptorProvider")]
Or simply call it in Application_Start method:
public class MvcApplication : HttpApplication
{
protected void Application_Start()
{
TypeDescriptorsConfig.InitializeCustomTypeDescriptorProvider();
// rest of init code ...
}
}
But this is not the end of the story. :(
Consider following model:
public class TestModel
{
[CustomBindingName("actual_name")]
[DisplayName("Yay!")]
public string TestProperty { get; set; }
}
If we try to write in .cshtml view something like:
#model Some.Namespace.TestModel
#Html.DisplayNameFor(x => x.TestProperty) #* fail *#
We will get ArgumentException:
An exception of type 'System.ArgumentException' occurred in System.Web.Mvc.dll but was not handled in user code
Additional information: The property Some.Namespace.TestModel.TestProperty could not be found.
That because all helpers soon or later invoke ModelMetadata.FromLambdaExpression method. And this method take expression we provided (x => x.TestProperty) and takes member name directly from member info and have no clue about any of our attributes, metadata (who cares, huh?):
internal static ModelMetadata FromLambdaExpression<TParameter, TValue>(/* ... */)
{
// ...
case ExpressionType.MemberAccess:
MemberExpression memberExpression = (MemberExpression) expression.Body;
propertyName = memberExpression.Member is PropertyInfo ? memberExpression.Member.Name : (string) null;
// I want to cry here - ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
// ...
}
For x => x.TestProperty (where x is TestModel) this method will return TestProperty, not actual_name, but model metadata contains actual_name property, have no TestProperty. That is why the property could not be found error thrown.
This is a design failure.
However despite this little inconvenience there are several workarounds, such as:
The easiest way is to access our members by theirs redefined names:
#model Some.Namespace.TestModel
#Html.DisplayName("actual_name") #* this will render "Yay!" *#
This is not good. No intellisense at all and as our model change we will have no any compilation errors. On any change anything can be broken and there is no easy way to detect that.
Another way is a bit more complex - we can create our own version of that helpers and forbid anybody from calling default helpers or ModelMetadata.FromLambdaExpression for model classes with renamed properties.
Finally, combination of previous two would be preferred: write own analogue to get property name with redefinition support, then pass that into default helper. Something like this:
#model Some.Namespace.TestModel
#Html.DisplayName(Html.For(x => x.TestProperty))
Compilation-time and intellisense support and no need to spend a lot of time for complete set of helpers. Profit!
Also everything described above work like a charm for model binding. During model binding process default binder also use metadata, gathered by TypeDescriptor.
But I guess binding json data is the best use case. You know, lots of web software and standards use lowercase_separated_by_underscores naming convention. Unfortunately this is not usual convention for C#. Having classes with members named in different convention looks ugly and can end up in troubles. Especially when you have tools that whining every time about naming violation.
ASP.NET MVC default model binder does not bind json to model the same way as it happens when you call newtonsoft's JsonConverter.DeserializeObject method. Instead, json parsed into dictionary. For example:
{
complex: {
text: "blabla",
value: 12.34
},
num: 1
}
will be translated into following dictionary:
{ "complex.text", "blabla" }
{ "complex.value", "12.34" }
{ "num", "1" }
And later these values along with others values from query string, route data and so on, collected by different implementations of IValueProvider, will be used by default binder to bind a model with help of metadata, gathered by TypeDescriptor.
So we came full circle from creating model, rendering, binding it back and use it.
The short answer is NO and long answer still NO. There is no built-in helper, attribute, model binder, whatever is it (Nothing out of box).
But what I did in before answer (I deleted it) was an awful solution that I realized yesterday. I am going to put it in github for who still wants to see (maybe it solves somebody problem) (I don't suggest it also!)
Now I searched it for again and I couldn't find anything helpful. If you are using something like AutoMapper or ValueInjecter like tool for mapping your ViewModel objects to Business objects and if you want to obfuscate that View Model parameters also, probably you are in some trouble. Of course you can do it but strongly typed html helpers are not going to help you alot. I even not talking about the if other developers taking branch and working over common view models.
Luckily my project (4 people working on it, and its commercial use for) not that big for now, so I decided to change View Model property names! (It is still lot work to do. Hundreds of view models to obfuscate their properties!!!) Thank you Asp.Net MVC !
There some ways in the links which I gave in question. But also if you still want to use the BindAlias attribute, I can only suggest you to use the following extension methods. At least you dont have to write same alias string which you write in BindAlias attribute.
Here it is:
public static string AliasNameFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper,
Expression<Func<TModel, TProperty>> expression)
{
var memberExpression = ExpressionHelpers.GetMemberExpression(expression);
if (memberExpression == null)
throw new InvalidOperationException("Expression must be a member expression");
var aliasAttr = memberExpression.Member.GetAttribute<BindAliasAttribute>();
if (aliasAttr != null)
{
return MvcHtmlString.Create(aliasAttr.Alias).ToHtmlString();
}
return htmlHelper.NameFor(expression).ToHtmlString();
}
public static string AliasIdFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper,
Expression<Func<TModel, TProperty>> expression)
{
var memberExpression = ExpressionHelpers.GetMemberExpression(expression);
if (memberExpression == null)
throw new InvalidOperationException("Expression must be a member expression");
var aliasAttr = memberExpression.Member.GetAttribute<BindAliasAttribute>();
if (aliasAttr != null)
{
return MvcHtmlString.Create(TagBuilder.CreateSanitizedId(aliasAttr.Alias)).ToHtmlString();
}
return htmlHelper.IdFor(expression).ToHtmlString();
}
public static T GetAttribute<T>(this ICustomAttributeProvider provider)
where T : Attribute
{
var attributes = provider.GetCustomAttributes(typeof(T), true);
return attributes.Length > 0 ? attributes[0] as T : null;
}
public static MemberExpression GetMemberExpression<TModel, TProperty>(Expression<Func<TModel, TProperty>> expression)
{
MemberExpression memberExpression;
if (expression.Body is UnaryExpression)
{
var unaryExpression = (UnaryExpression)expression.Body;
memberExpression = (MemberExpression)unaryExpression.Operand;
}
else
{
memberExpression = (MemberExpression)expression.Body;
}
return memberExpression;
}
When you want to use it:
[ModelBinder(typeof(AliasModelBinder))]
public class FilterViewModel
{
[BindAlias("someText")]
public string FilterParameter { get; set; }
}
In html:
#* at least you dont write "someText" here again *#
#Html.Editor(Html.AliasNameFor(model => model.FilterParameter))
#Html.ValidationMessage(Html.AliasNameFor(model => model.FilterParameter))
So I am leaving this answer here like this. This is even not an answer (and there is no answer for MVC 5) but who searching in google for same problem might find useful this experience.
And here is the github repo: https://github.com/yusufuzun/so-view-model-bind-20869735
I'm writing an HTML Helper for an editor. The idea is to get properties from the Model with attributes AutoGenerateField and build a table, each line of which contains a name of a field (also from the attribute) and a TextBox or a CheckBox containing actual value of the field.
I have a problem with HTMLHelper. Since I send the whole model to the helper and not one value, I cannot use methods such as TextBoxFor, as they need parameter, such as
"Expression<Func<TModel, TValue>> expression".
I'm using reflexion and I tried to send the property instead, still VisualStudio considers this as incorrect usage.
Below is simplified method for my HtmlHelper:
public static MvcHtmlString GenerateEditor<TModel>(this HtmlHelper<TModel> htmlHelper)
{
var model = htmlHelper.ViewData.Model;
var result = String.Empty;
//generating container, etc ...
foreach (var property in model.GetType().GetProperties())
{
var attr = property.GetCustomAttributes(typeof (DisplayAttribute), true).FirstOrDefault();
if (attr == null) continue;
var autoGenerate = ((DisplayAttribute)attr).AutoGenerateField;
if(autoGenerate)
{
//here I'm building the html string
//My problem is in the line below:
var r = htmlHelper.TextBoxFor(property);
}
}
return MvcHtmlString.Create(result);
}
Any ideas?
How about just using the non-lambda overloads. : InputExtensions.TextBox()
if(autoGenerate)
{
//here I'm building the html string
//My problem is in the line below:
var r = htmlHelper.TextBox(property.Name);
}
//not sure what you do with r from here...
If I'm not mistaken the name attribute of the form element is set to the property name even when you use the lambda version of the function so this should do the same thing.
I will try and verify what the lambda function does, you might be able to do the same since you have the TModel with you.
Update
From a quick look of things inside the source code of InputExtensions.cs, TextBoxFor calls eventually calls InputHelper() which eventually calls ExpressionHelper.GetExpressionText(LambdaExpression expression) inside ExpressionHelper.cs which from the cursory looks of things gets the member.Name for the name html attribute on the input element.
I can't quite verify it right now because I'm not on windows but I think the non-lambda function should suit your need. Do tell me how it goes?
Is there any useful hook in ASP.NET MVC (MVC4) which can let you access the Action method parameter (View model) before the action method becomes invoked, and then also (e.g. depending on the value of something you checked in the action method parameter) let you prevent the action method from being invoked, i.e. instead either forward the view model object (action method parameter) to another action method or directly to some view (i.e. without any further processing in an action method) ?
If you do not understand the question, please see the code example below which should illustrate the kind of code I am looking for...
(though I do not know if there actually exists such kind of interface and a possibility to hook an implementation into the MVC framework)
If this is indeed possible, I would like to see an answer with code example about how to do it (and not just a response with someone claiming that e.g. "try using method 'ActionFilterAttribute.OnActionExecuting' or 'IModelBinder.BindModel' " because I have already tried those and could not make it work).
Also, please respect that I do not want this thread to become a discussion about WHY to do it, but want to see HOW to do it.
(i.e. I am not interested in getting into discussions with responses such as "What are you actually trying to achieve?" or "There are probably better things of doing what you want to do...")
The question can be split into three subquestions/code examples as my own code samples below try to illustrate:
(but would like them "refactored" into REAL code with usage of real existing types)
(obviously, every type below which includes the substring "Some" is something I have made up, and I am looking for the corresponding real thing ...)
(1) Example of how to get access to (and potentially modify) view model objects (action method parameters) in a generic place before the actual action method is invoked with the view model object parameter.
The kind of code example I am looking for would probably be similar to below but do not know what kind of interface to use and how to register it to be able to do something like below:
public class SomeClass: ISomeInterface { // How to register this kind of hook in Application_Start ?
public void SomeMethodSomewhere(SomeActionMethodContext actionMethodContext, object actionMethodParameterViewModel) {
string nameOfTheControllerAboutToBeInvoked = actionMethodContext.ControllerName;
string nameOfTheActionMethodAboutToBeInvoked = actionMethodContext.MethodName;
// the above strings are not used below but just used for illustrating that the "context object" contains information about the action method to become invoked by the MVC framework
if(typeof(IMyBaseInterfaceForAllMyViewModels).IsAssignableFrom(actionMethodParameterViewModel.GetType())) {
IMyBaseInterfaceForAllMyViewModels viewModel = (IMyBaseInterfaceForAllMyViewModels) actionMethodParameterViewModel;
// check something in the view model:
if(viewModel.MyFirstGeneralPropertyInAllViewModels == "foo") {
// modify something in the view model before it will be passed to the target action method
viewModel.MySecondGeneralPropertyInAllViewModels = "bar";
}
}
}
}
(2) Example of how to prevent the targeted action method from being executed and instead invoke another action method.
The example might be an extension of the above example, with something like below:
public void SomeMethodSomewhere(SomeActionMethodContext actionMethodContext, object actionMethodParameterViewModel) {
... same as above ...
if(viewModel.MyFirstGeneralPropertyInAllViewModels == "foo") {
actionMethodContext.ControllerName = "SomeOtherController";
actionMethodContext.MethodName = "SomeOtherActionMethod";
// The above is just one example of how I imagine this kind of thing could be implemented with changing properties, and below is another example of doing it with a method invocation:
SomeHelper.PreventCurrentlyTargetedActionMethodFromBecomingExecutedAndInsteadExecuteActionMethod("SomeOtherController", "SomeOtherActionMethod", actionMethodParameterViewModel);
// Note that I do _NOT_ want to trigger a new http request with something like the method "Controller.RedirectToAction"
}
(3) Example of how to prevent the normal action method from being executed and instead forward the view model object directly to a view without any further processing.
The example would be an extension of the first above example, with something like below:
public void SomeMethodSomewhere(SomeActionMethodContext actionMethodContext, object actionMethodParameterViewModel) {
... same as the first example above ...
if(viewModel.MyFirstGeneralPropertyInAllViewModels == "foo") {
// the below used razor view must of course be implemented with a proper type for the model (e.g. interface 'IMyBaseInterfaceForAllMyViewModels' as used in first example above)
SomeHelper.PreventCurrentlyTargetedActionMethodFromBecomingExecutedAndInsteadForwardViewModelToView("SomeViewName.cshtml", actionMethodParameterViewModel);
}
You could use an action filter and override the OnActionExecuting event:
public class MyActionFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
...
}
}
Now let's see what useful information you could extract from this filterContext argument that is passed to this method. The property you should be looking for is called ActionParameters and represents an IDictionary<string, object>. As its name suggests this property contains all the parameters that are passed to the controller action by name and value.
So let's suppose that you have the following controller action:
[MyActionFilter]
public ActionResult Index(MyViewModel model)
{
...
}
Here's how you could retrieve the value of the view model after model binding:
public class MyActionFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
var model = filterContext.ActionParameters["model"] as MyViewModel;
// do something with the model
// You could change some of its properties here
}
}
Now let's see the second part of your question. How to shortcircuit the controller action and redirect to another action?
This could be done by assigning a value to the Result property:
public class MyActionFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
... some processing here and you decide to redirect:
var routeValues = new RouteValueDictionary(new
{
controller = "somecontroller",
action = "someaction"
});
filterContext.Result = new RedirectToRouteResult(routeValues);
}
}
or for example you decide to shortcircuit the execution of the controller action and directly render a view:
public class MyActionFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
var viewResult = new ViewResult
{
ViewName = "~/Views/FooBar/Baz.cshtml",
};
MyViewModel someModel = ... get the model you want to pass to the view
viewResult.ViewData.Model = model;
filterContext.Result = viewResult;
}
}
or you might decide to render a JSON result:
public class MyActionFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
MyViewModel someModel = ... get the model you want to pass to the view
filterContext.Result = new JsonResult
{
Data = model,
JsonRequestBehavior = JsonRequestBehavior.AllowGet
};
}
}
So as you can see the possibilities are unlimited of what you can do.
I have experimented with the code in the answer provided by the user Darin Dimitrov, and the first and third parts of the answer are correct.
(Though, for others who might find this thread and be interested, I can clarify that in the first answer the "model" does not seem to
be a hardcoded keyword always used for the model but seems to have to correspond to the chosen name of the action method parameter.
In other words, if you instead have the method signature
public ActionResult Index(MyViewModel myViewModel)
then in your action filter you have to use
var model = filterContext.ActionParameters["myViewModel"] as MyViewModel;
)
Regarding the second answer, the usage of 'RedirectToRouteResult' will trigger a new http request (which was not desired as I mentioned in the second code example of mine).
I found another way of "changing" action method by actually invoking it explicitly:
var controller = new SomeController();
ActionResult result = controller.SomeAction(model);
filterContext.Result = result;
The above code actually seems to prevent the originally targeted action method from becoming invoked, i.e. when I put a breakpoint in the method annotated with '[MyActionFilter]' the execution never got into that method.
Typically, it is probably not desired to hardcode a controller like above, but instead reflection might be used, for example as below with the thirdpart library "fasterflect":
string nameOfController = ...
string nameOfActionMethod = ...
// both above variables might for example be derived by using some naming convention and parsing the refering url, depending on what you want to do ...
var theController = this.GetType().Assembly.CreateInstance(nameOfController);
ActionResult result = (ActionResult)theController.CallMethod(nameOfActionMethod, model);
filterContext.Result = result;
(for those who want to extract the names of the current target controller and action method, when implementing logic to determine the controller you want to invoke, you can use this code in the filter:
var routeValueDictionary = filterContext.RouteData.Values;
string nameOfTargetedController = routeValueDictionary["controller"].ToString();
string nameOfTargetedActionMethod = routeValueDictionary["action"].ToString();
)
I think it feels a bit awkward to instantiate and invoke controllers like above, and would prefer to change the target controller and action method in another way if possible ?
So, the remaining question is if there is still (in MVC 4 final version) no way of redirecting/forwarding execution "internally" (without a new http request being fired as with 'RedirectToAction') at the server ?
Basically, I think I am here just looking for something like "Server.Transfer" which was used with ASP.NET Web Forms (and also the old classic ASP I believe could use the same thing).
I have seen older question/answers on this issue with people implementing this behaviour themselves with some "TransferResult" class of their own, but it seems to tend to become broken i different MVC versions.
(for example, see here for MVC 4 beta: How to redirect MVC action without returning 301? (using MVC 4 beta) ).
Is there really still not a simple standard solution (implemented in MVC 4 final) about how to do an "internal redirect" without a new http request (as RedirectToAction does) ?
I have two separate classes derived from the same interface, but have different validation/data annotations assigned. The requirement is that the same data needs to be collected, but on one screen nothing is required (a save screen), but on the other there are some required fields (a submit/finalize screen.)
I've made a PartialView that is to be used in two separate View, one for save, one for final submit.
I've tried using the parent Interface as the View's model, however my validators don't fire (as I expect, I'm guessing that because the Interface itself doesn't have any annotations, nothing will fire.) Is there a way to have the page dynamically choose one class or the other depending on which page I'm using instead of the Interface?
As a side-note, this is being done in ASP.net MVC 3 with Razor.
You can achieve what you want with one class, and a little lateral thinking.
First, create your class, with the validation baked in. Next, create a custom ModelValidatorProvider inheriting from DataAnnotationsModelValidatorProvider, like so:
public class MyMetadataValidatorProvider : DataAnnotationsModelValidatorProvider
{
protected override IEnumerable<ModelValidator> GetValidators(ModelMetadata metadata, ControllerContext context, IEnumerable<Attribute> attributes)
{
var vals = base.GetValidators(metadata, context, attributes);
// check to see if any keys have been inserted
if (context.Controller.ViewData.Keys.Count > 0)
{
// check if we have a key named "NoValidate" with a value of true
// do not return the validtors if we do
if ((bool)context.Controller.ViewData.FirstOrDefault(k => k.Key == "NoValidate").Value)
{
// we do not want to return our validators, return an empty list
return new List<ModelValidator>();
}
}
else
{
// check if the form has a key named "NoValidate" with a value of true
// do not return the validtors if we do
if (context.HttpContext.Request.Form["NoValidate"].ToLowerInvariant() == "true")
{
// we do not want to return our validators, return an empty list
return new List<ModelValidator>();
}
}
// we want to return our validators
return vals;
}
}
Next, register the custom ModelValidatorProvider in Application_Start in Global.asax.cs, like so:
ModelValidatorProviders.Providers.Clear();
ModelValidatorProviders.Providers.Add(new MyMetadataValidatorProvider());
Then, add the following to your view (this will govern whether the validators are returned when the form is POSTed):
#Html.Hidden("NoValidate", ViewData.FirstOrDefault(k => k.Key == "NoValidate").Value)
Finally, add actions like the following:
public ActionResult Index()
{
var model = new MyModel();
// this will set validation to appear
ViewData.Add("NoValidate", false);
// this will suppress validation
ViewData.Add("NoValidate", true);
return View(model);
}
[HttpPost]
public ActionResult Index(MyModel model)
{
// we DO want validation, so let's test for it in addition
// to testing if the ModelState is valid
if (Request.Form["NoValidate"].ToLowerInvariant() != "true" && ModelState.IsValid)
{
ModelState.Clear();
var newmodel = new MyModel();
ViewData.Add("NoValidate", true);
return View(newmodel);
}
ViewData.Add("NoValidate", false);
return View(model);
}
Note that you can control whether the validation appears in your GET action by setting the NoValidate key in ViewData as you want. On the POST, the validation is governed by the form value for NoValidate.
IMPORTANT NOTE: In your action which requires validation, you need to add a test to confirm that the Form does not have the key NoValidate, or its value is not True, in order to enforce that a user cannot avoid the validation.
UPDATE
At first, I had validation only appearing when certain conditions were true. Idecided this was a BAD IDEA, so now validation will only be suppressed if the conditions are true.
Each view should be strongly typed to a separate view model. Each viewmodel then has the validation logic on it (annotations) or inherits from a base that has the required validation on it.
Any logic that cannot be inherited is simply set on your ViewModel itself. If its a small moderl I would consider just copy/paste and two separate viewmodels with their own set of attributes.
You can use AutoMapper to easily map between some concrete object that implements your interface and your ViewModels.
Could you use one class? You can create a filter that allows you to manage the validation errors for an action. In your case you can add an attribute to the Save action and ignore the required errors, but the validations will run for the submit/finalize action. This example will discard all the errors.
public class DontValidateEmailAttribute : ActionFilterAttribute {
public override void OnActionExecuting(ActionExecutingContext filterContext) {
var modelState = filterContext.Controller.ViewData.ModelState;
var incomingValues = filterContext.Controller.ValueProvider;
foreach (var key in modelState.Keys)
modelState[key].Errors.Clear();
}
}
I learnt this technique from Steve Sanderson's Pro ASP NET MVC 3. He uses the technique to validate a model that has required fields but the data entry is a multistep wizard. If the value has not been returned in the form post, he removes the errors for that property.
My current problem is that I have a partial view that I want to determine what model is being used by it.
I have had to deal with a few strange scenarios for my project so I will try to outline it here, maybe someone can offer a better way to do this.
I am designing something like the Google iGoogle page. A main page with multiple widgets that are able to move around or be configured as needed. The current system loads the actual widget's data asynchronously view a POST to a controller within my application. That controller will either render a partial view to HTML that can be returned (and then loaded into the page view JQUERY) or just straight HTML/JavaScript that is stored in a database.
This was working fine for me, I had a model for the widgets that holds a dictionary of options that are described via the database, and then used by the partial view. The problem came when I wanted to pass data to a partial view. The best solution I could come up with was having the controller determine which model the partial view in question uses, have some function that will fill the model, and then pass it, along with the partial view, to the function that will render it to HTML within the controller.
I realize this is an odd scenario for MVC (the layers are blending...) and any advice on fundamental design, or implementation of this would be greatly appreciated.
I am currently using MVC3/Razor. Feel free to ask any other questions.
I prototyped a possible solution to this, because it seemed like a fun problem. I hope it's useful to you.
Models
First, the models. I decided to create two 'widgets', one for news, and one for a clock.
public class NewsModel
{
public string[] Headlines { get; set; }
public NewsModel(params string[] headlines)
{
Headlines = headlines;
}
}
public class ClockModel
{
public DateTime Now { get; set; }
public ClockModel(DateTime now)
{
Now = now;
}
}
Controller
My controller doesn't know anything about the views. What it does is returns a single model, but that model has the ability to dynamically fetch the right model as required by the view.
public ActionResult Show(string widgetName)
{
var selector = new ModelSelector();
selector.WhenRendering<ClockModel>(() => new ClockModel(DateTime.Now));
selector.WhenRendering<NewsModel>(() => new NewsModel("Headline 1", "Headline 2", "Headline 3"));
return PartialView(widgetName, selector);
}
Delegates are used so that the correct model is only created/fetched if it is actually used.
ModelSelector
The ModelSelector that the controller uses is pretty simple - it just keeps a bag of delegates to create each model type:
public class ModelSelector
{
private readonly Dictionary<Type, Func<object>> modelLookup = new Dictionary<Type, Func<object>>();
public void WhenRendering<T>(Func<object> getter)
{
modelLookup.Add(typeof(T), getter);
}
public object GetModel(Type modelType)
{
if (!modelLookup.ContainsKey(modelType))
{
throw new KeyNotFoundException(string.Format("A provider for the model type '{0}' was not provided", modelType.FullName));
}
return modelLookup[modelType]();
}
}
The Views - Simple solution
Now, the easiest way to implement a view would be:
#model MvcApplication2.ModelSelector
#using MvcApplication2.Models
#{
var clock = (ClockModel) Model.GetModel(typeof (ClockModel));
}
<h2>The time is: #clock.Now</h2>
You could end here and use this approach.
The Views - Better solution
That's pretty ugly. I wanted my views to look like this:
#model MvcApplication2.Models.ClockModel
<h2>Clock</h2>
#Model.Now
And
#model MvcApplication2.Models.NewsModel
<h2>News Widget</h2>
#foreach (var headline in Model.Headlines)
{
<h3>#headline</h3>
}
To make this work, I had to create a custom view engine.
Custom view engine
When a Razor view is compiled, it inherits a ViewPage<T>, where T is the #model. So we can use reflection to figure out what type the view wanted, and select it.
public class ModelSelectorEnabledRazorViewEngine : RazorViewEngine
{
protected override IView CreateView(ControllerContext controllerContext, string viewPath, string masterPath)
{
var result = base.CreateView(controllerContext, viewPath, masterPath);
if (result == null)
return null;
return new CustomRazorView((RazorView) result);
}
protected override IView CreatePartialView(ControllerContext controllerContext, string partialPath)
{
var result = base.CreatePartialView(controllerContext, partialPath);
if (result == null)
return null;
return new CustomRazorView((RazorView)result);
}
public class CustomRazorView : IView
{
private readonly RazorView view;
public CustomRazorView(RazorView view)
{
this.view = view;
}
public void Render(ViewContext viewContext, TextWriter writer)
{
var modelSelector = viewContext.ViewData.Model as ModelSelector;
if (modelSelector == null)
{
// This is not a widget, so fall back to stock-standard MVC/Razor rendering
view.Render(viewContext, writer);
return;
}
// We need to work out what #model is on the view, so that we can pass the correct model to it.
// We can do this by using reflection over the compiled views, since Razor views implement a
// ViewPage<T>, where T is the #model value.
var compiledViewType = BuildManager.GetCompiledType(view.ViewPath);
var baseType = compiledViewType.BaseType;
if (baseType == null || !baseType.IsGenericType)
{
throw new Exception(string.Format("When the view '{0}' was compiled, the resulting type was '{1}', with base type '{2}'. I expected a base type with a single generic argument; I don't know how to handle this type.", view.ViewPath, compiledViewType, baseType));
}
// This will be the value of #model
var modelType = baseType.GetGenericArguments()[0];
if (modelType == typeof(object))
{
// When no #model is set, the result is a ViewPage<object>
throw new Exception(string.Format("The view '{0}' needs to include the #model directive to specify the model type. Did you forget to include an #model line?", view.ViewPath));
}
var model = modelSelector.GetModel(modelType);
// Switch the current model from the ModelSelector to the value of #model
viewContext.ViewData.Model = model;
view.Render(viewContext, writer);
}
}
}
The view engine is registered by putting this in Global.asax.cs:
ViewEngines.Engines.Clear();
ViewEngines.Engines.Add(new ModelSelectorEnabledRazorViewEngine());
Rendering
My home view includes the following lines to test it all out:
#Html.Action("Show", "Widget", new { widgetName = "Clock" })
#Html.Action("Show", "Widget", new { widgetName = "News" })
One option would be to extend the idea of partial requests in your application. Steve Sanderson has a fantastic example of this, although the post relates to MVC 1 & 2. I think it would still help in you v3, but I haven't investigated v3 to see if the MVC team implemented their own version. In your asynch scenario, you'll need to toy with the implementation a bit, perhaps change the PartialRequest definition to accept different information as needed, but I think this might be a good start. The net result would be better isolation of concerns, allowing individual controllers to manage a particular type of partial, and in turn be better aware of the model Type you want to work with.
I'm not 100% sure that this is what you'd be looking for, but the [ChildActionOnly] attribute can be added to a method within your controller. That requires that the method can only be called from a partial view. Then you can set up your partial view for that method that basically resembles one of your widgets. Check out the MVC Music Store example here:
http://www.asp.net/mvc/tutorials/mvc-music-store-part-10
What about a dynamic view model? Layouts in MVC3 use them, and maybe you can use something similar for your purposes:
Dynamic in C# 4.0: Introducing the ExpandoObject
Fun With Method Missing and C# 4
Dynamic View Page, MVC without a View Model
I blogged about doing exactly this. Please see http://blogs.planetcloud.co.uk/mygreatdiscovery/?tag=/widget
Essentially I built out a similar widget system. The posts also cover how to handle configuration of those widgets. This makes use of the dynamic support in Mvc3 so that any model object can be passed to the view, from a single controller action.
By default all widgets have a collection of KVP properties (I believe this is what the OP has). So for a simple widget we get access to those properties from within the view. I used for a widget that displayed some html (where the html was stored in one of those properties).
However, for more complex widgets we implement IWidgetWithDisplayModel. This tells us that before we pass the loaded widget back to the view, we need to "build" our display model.
Here's the controller action that does that. Check the posts for full details.
[HttpGet]
public ActionResult Get(string name)
{
var widget = widgetService.GetWidgetBySystemName(name, true);
if (widget == null)
return Content(string.Format("Widget [{0}] not found!", name));
if (!this.ViewExists(widget.WidgetName))
return Content(string.Format("A template for widget [{0}] was not found.", widget.WidgetName));
if (widget is IWidgetWithDisplayModel) {
(widget as IWidgetWithDisplayModel).CreateDisplayModel();
}
return PartialView(widget.WidgetName, widget);
}