I'm developing a library for use in ASP.NET Core MVC. For this library, I need to get a list of all (compiled) Razor views (path and content) that exist in the application.
Is there a way to lookup all compiled Razor views in the application during runtime? So far I have not had any luck trying to find out.
Iterating through .cshtml files is no option because they will not be published when using compiled views.
For getting complied views path, you could try ViewsFeature like
public class HomeController : Controller
{
private readonly IViewCompilerProvider _viewCompilerProvider;
private readonly ApplicationPartManager _applicationPartManager;
public HomeController(IViewCompilerProvider viewCompilerProvider
, ApplicationPartManager applicationPartManager)
{
_viewCompilerProvider = viewCompilerProvider;
_applicationPartManager = applicationPartManager;
}
public IActionResult Index()
{
var feature = new ViewsFeature();
_applicationPartManager.PopulateFeature(feature);
var views = feature.ViewDescriptors;
return View();
}
}
Related
I need to dynamically creates controllers in a ASP.NET Core 6 MVC application.
I found some way to somewhat achieve this but not quite.
I'm able to dynamically add my controller but somehow it reflects only on the second request.
So here is what I do: first I initialize my console app as follows:
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Mvc.ApplicationParts;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.AspNetCore.Mvc.Infrastructure;
namespace DynamicControllerServer
{
internal class Program
{
static void Main(string[] args)
{
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();
ApplicationPartManager partManager = builder.Services.AddMvc().PartManager;
// Store thePartManager in my Middleware to be able to add controlelr after initialization is done
MyMiddleware._partManager = partManager;
// Register controller change event
builder.Services.AddSingleton<IActionDescriptorChangeProvider>(MyActionDescriptorChangeProvider.Instance);
builder.Services.AddSingleton(MyActionDescriptorChangeProvider.Instance);
var app = builder.Build();
app.UseAuthorization();
app.MapControllers();
// Add Middleware which is responsible to cactn the request and dynamically add the missing controller
app.UseMiddleware<MyMiddleware>();
app.RunAsync();
Console.WriteLine("Server has been started successfully ...");
Console.ReadLine();
}
}
}
Then my middleware looks like this: it basically detects that there is the "dynamic" keyword in the url. If so, it will load the assembly containing the DynamicController:
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.ApplicationParts;
using System;
using System.Reflection;
namespace DynamicControllerServer
{
public class MyMiddleware
{
public RequestDelegate _next { get; }
private string dllName = "DynamicController1.dll";
static public ApplicationPartManager _partManager = null;
public MyMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task Invoke(HttpContext httpContext)
{
if (httpContext.Request.Path.HasValue)
{
var queryParams = httpContext.Request.Path.Value;
if(httpContext.Request.Path.Value.Contains("api/dynamic"))
{
// Dynamically load assembly
Assembly assembly = assembly = Assembly.LoadFrom(#"C:\Temp\" + dllName);
// Add controller to the application
AssemblyPart _part = new AssemblyPart(assembly);
_partManager.ApplicationParts.Add(_part);
// Notify change
MyActionDescriptorChangeProvider.Instance.HasChanged = true;
MyActionDescriptorChangeProvider.Instance.TokenSource.Cancel();
}
}
await _next(httpContext); // calling next middleware
}
}
}
The ActionDescriptorChange provider looks like this:
using Microsoft.AspNetCore.Mvc.Infrastructure;
using Microsoft.Extensions.Primitives;
namespace DynamicControllerServer
{
public class MyActionDescriptorChangeProvider : IActionDescriptorChangeProvider
{
public static MyActionDescriptorChangeProvider Instance { get; } = new MyActionDescriptorChangeProvider();
public CancellationTokenSource TokenSource { get; private set; }
public bool HasChanged { get; set; }
public IChangeToken GetChangeToken()
{
TokenSource = new CancellationTokenSource();
return new CancellationChangeToken(TokenSource.Token);
}
}
}
Dynamic controller is in separate dll and is very simple:
using Microsoft.AspNetCore.Mvc;
namespace DotNotSelfHostedOwin
{
[Route("api/[controller]")]
[ApiController]
public class DynamicController : ControllerBase
{
public string[] Get()
{
return new string[] { "dynamic1", "dynamic1", DateTime.Now.ToString() };
}
}
}
Here are the packages used in that project:
<PackageReference Include="Microsoft.AspNetCore" Version="2.2.0" />
<PackageReference Include="Swashbuckle.AspNetCore" Version="6.2.3" />
This works "almost" fine ... when first request is made to:
https://localhost:5001/api/dynamic
then it goes in the middleware and load the assembly, but returns a 404 error.
Then second request will actually work as expected:
Second request returns the expected result:
I must doing it wrong and probably my middleware is executed too late in the flow to reflect the dynamic controller right away.
Question is: what should be the proper way to achieve this?
Second question I have is say now the external dll holding our dynamic controller is updated.
How can I reload that controller to get the new definition?
Any help would be appreciated
Thanks in advance
Nick
Here is the answer to my own question in case it can help somebody out there.
It seems building and loading the controller from the middleware will always end up with failure on the first call.
This makes sense since we are already in the http pipeline.
I end up doing same thing from outside the middleware.
Basically my application detect a change in the controller assembly, unload the original assembly and load the new one.
You cannot use the Default context since it will not allow reloading different dll for same assembly:
var assembly = AssemblyLoadContext.Default.LoadFromAssemblyPath(assemblyPath); // Produce an exception on updates
To be able to reload new dll for same assembly, I’m loading each controller in its own assembly context. To do that you need to create your own class deriving from AssemblyLoadContext and managing assembly load:
public class MyOwnContext: AssemblyLoadContext
{
// You can find lots of example in the net
}
When you want to unload the assembly, you just unload the context:
MyOwnContextObj.Unload();
Now to add or remove the controller on the fly, you need to keep reference of the PartManager and the ApplicationPart.
To add controller
ApplicationPart part = new AssemblyPart(assembly);
_PartManager.ApplicationParts.Add(part);
To remove:
_PartManager.ApplicationParts.Remove(part);
On course once done, still use following piece of code to acknowledge the change:
MyActionDescriptorChangeProvider.Instance.HasChanged = true;
MyActionDescriptorChangeProvider.Instance.TokenSource.Cancel();
That allow updating controller on the fly with no interruption of service.
Hope this helps people out there.
I have done a similar solution (used for managing a web app plugins) with some differences that may help you:
List all the external assemblies in a config file or appsettings.json so all the dll names and/or addresses are known at startup
Instead of registering controllers when they are called, register them at program.cs/start up :
//Foreah dllName from settings file
var assembly = Assembly.LoadFrom(#"Base address" + dllNameLoadedFromSettings);
var part = new AssemblyPart(assembly);
services.AddControllersWithViews()
.ConfigureApplicationPartManager(apm => apm.ApplicationParts.Add(part));
// Any other configuration based on the usage you want
Second: I usually keep plugin dlls in the bin folder so when using IIS as soon as a dll file in bin is changed the upper-level app is automatically reset. So your second question would be solved too.
I'd like to create a ViewHelper to localize my ASP.NET MVC application. Something like this:
public class Translator
{
private readonly ITranslationRepository _repo;
public Translator(ITranslationRepository repo)
{
_repo = repo;
}
public static string Translate(TranslationEnum translationEnum)
{
return _repo.GetTranslation(translationEnum, Session.LanguageId);
}
}
Usage in a (Razor) View looks like this:
<p>#Translator.Translate(TranslationEnum.WelcomeMessage)</p>
Now the problem is of course, I cannot make the Translate method static, because I need to access the instance variable _repo.
How can I inject the repository into a ViewHelper so I can use it in a View like above?
The responsibility of the view is just to transform the data that comes back from the controller to a HTML structure. Views are hard (to impossible) to test automatically, so best is to keep them as dumb as possible.
Instead of using the Translator in your view, inject it into your controller and let the controller call the Translator. This solves a range of problems:
It keeps the view simple.
It improves maintainability.
It improves testability.
It improves the verifiability of your object graphs (because you don't fall back on static method calls or the Service Locator anti-pattern).
Long story short, add a property to the controller's view model and return that to the view. Example:
public class HomeController : Controller {
private readonly ITranslator translator;
public HomeController(ITranslator translator) {
this.translator = translator
}
public ActionResult Index() {
this.View(new HomeViewModel {
WelcomeMessage = this.translator.Translate(TranslationEnum.WelcomeMessage)
});
}
}
And your view can look as follows:
#model HomeViewModel
<p>#Model.WelcomeMessage</p>
first of all, the intention of your design is wrong because it violates the single responsibility principal. Why is a translator dependent on repository?
secondly, why do you need a translator, you can use asp.net globalization?
click me We should not reinvent the wheel.
thirdly, all the html helpers are extension methods which have to be static.
so my suggestion is if you have to use translator, please refactor the Translator class, decouple the repository from it then create a extension methods from there.
or you can use globalization, it sounds horrible to start with but trust me it's not as hard as it looks.
public class Translator
{
private static ITranslationRepository _repo;
public static ITranslationRepository Repo
{
get { /*check null here before return*/ return _repo; } set { _repo = Repo; }
}
public Translator()
{
}
public static string Translate(TranslationEnum translationEnum)
{
return _repo.GetTranslation(translationEnum, Session.LanguageId);
}
}
I like the idea of Steven Sanderson's Partial Requests in http://blog.stevensanderson.com/2008/10/14/partial-requests-in-aspnet-mvc/ and I'm trying to get it to work with Razor pages. Unfortunately it writes it to the top of the page, instead of where I actually want it to be in the document. I'm guessing the problem is similar to the one answered here: ASP.Net MVC 3 Razor Response.Write position but I don't know how to get around it.
Can anyone supply me with a workaround? Failing that, is there simply another good technique for rendering the contents of another action in a view, without that view having to know about the action?
Yes, it is possible.
As I'm sure you're now aware the Razor view engine writes to temporary buffers before writing to the response stream, which is why when you invoke another action the markup gets written to the response out of order.
The workaround that I've used in the past is to temporarily redirect any writes to the response to a MemoryStream while you are trying to render another action, and then creating a MvcHtmlString from the contents of the MemoryStream.
So something like:
public class HttpResonseCapture : IDisposable
{
private readonly MemoryStream _stream = new MemoryStream();
private readonly Stream _originalStream;
private readonly HttpContextBase _httpContext;
public HttpResponseCapture(HttpContextBase httpContext)
{
_httpContext = httpContext;
_originalStream = httpContext.Response.OutputStream;
httpContext.Response.OutputStream = _stream;
}
public MvcHtmlString ToHtmlString()
{
return MvcHtmlString.Create(Encoding.Unicode.GetString(_stream.ToArray()));
}
public void Dispose()
{
_httpContext.Response.OutputStream = _originalStream;
_stream.Dispose();
}
}
Can be used like so:
using (var responseCapture = new HttpResponseCapture(httpContext))
{
// Call other action here
var result = responseCapture.ToHtmlString();
}
In our project we're using the razorgenerator of David Ebbo. This allowed us to move some of our cshtml files to a class library.
What we would like to achieve now is the following:
MyCommonViews has a "MyView.cshtml" in its Views folder.
MyWebProject ALSO has a "MyView.cshtml" in its Views folder.
MyOtherWebProject DOES NOT have a "MyView.cshtml" in its Views folder.
When MyOtherWebProject needs to load MyView.cshtml, it will pick the one which is in the compiled MyCommonViews project. That is what we want.
BUT when MyWebProject needs to load MyView.cshtml, we would like it to pick up the "overridden" MyView.cshtml file which is in the MyWebProject itself.
Is what we want possible and how?
Manu.
I wrote up a hacky solution for our problem. It hacks into the razorgenerators viewengine and removes all appropriate entries from the (private readonly) Dictionary it has.
The code is ran on application start.
Talk is cheap, show me the code:
private static void HackRazorGeneratorToAllowViewOverriding()
{
// first we search for the PrecompiledMvcEngine
var razorGeneratorViewEngine = ViewEngines.Engines.ToList().FirstOrDefault(ve => ve.GetType().Name.Contains("PrecompiledMvcEngine"));
if (razorGeneratorViewEngine == null)
return;
// retrieve the dictionary where it keeps the mapping between a view path and the (view object) type to instantiate
var razorMappings = (IDictionary<string, Type>)ReflectionUtils.GetPrivateReadonly("_mappings", razorGeneratorViewEngine);
// retrieve a list of all our cshtml files in our 'concrete' web project
var files = Directory.GetFiles(Path.Combine(WebConfigSettings.RootPath, "Views"), "*.cshtml", SearchOption.AllDirectories);
// do some kungfu on those file paths so that they are in the same format as in the razor mapping dictionary
var concreteViewPaths = files.Select(fp => string.Format("~{0}", fp.Replace(WebConfigSettings.RootPath, "").Replace(#"\", "/"))).ToList();
// loop through each of the cshtml paths (of our 'concrete' project) and remove it from the razor mappings if it's there
concreteViewPaths.ForEach(vp =>
{
if (razorMappings.ContainsKey(vp))
razorMappings.Remove(vp);
});
}
WebConfigSettings.RootPath contains the path on HD to the root of our web application.
This is a part of our static ReflectionUtils class:
/// <summary>
/// Get a field that is 'private readonly'.
/// </summary>
public static object GetPrivateReadonly(string readonlyPropName, object instance)
{
var field = instance.GetType().GetField(readonlyPropName, BindingFlags.Instance | BindingFlags.NonPublic);
if (field == null)
throw new NullReferenceException(string.Format("private readonly field '{0}' not found in '{1}'", readonlyPropName, instance));
return field.GetValue(instance);
}
This did the trick. We basically force the PrecompiledMvcEngine to "forget" any view which we have in our concrete project.
You can also try CompositePrecompiledMvcEngine from RazorGenerator.Mvc 2.1.0. It was designed for correct support of view overriding within multiple assemblies. Piece of code:
var engine = new CompositePrecompiledMvcEngine(
/*1*/ PrecompiledViewAssembly.OfType<MyCommonViewsSomeClass>(),
/*2*/ PrecompiledViewAssembly.OfType<MyWebProjectSomeClass>(
usePhysicalViewsIfNewer: HttpContext.Current.IsDebuggingEnabled));
ViewEngines.Engines.Insert(0, engine);
VirtualPathFactoryManager.RegisterVirtualPathFactory(engine);
The first line will register all views from the MyCommonViews assembly (~/Views/MyView.cshtml), the second line will register all views from the MyWebProject or MyOtherWebProject assembly.
When it encounters the virtual path, that already has been registered (~/Views/MyView.cshtml from the MyWebProject assembly), it overrides an old mapping with a new view type mapping.
If another project doesn't has view with the same virtual path (MyOtherWebProject) it leaves source mapping unchanged.
There is flag PreemptPhysicalFiles = false which does the magic.
Full sample:
[assembly: WebActivator.PostApplicationStartMethod(typeof(Application.Web.Common.App_Start.RazorGeneratorMvcStart), "Start")]
namespace Application.Web.Common.App_Start
{
public static class RazorGeneratorMvcStart
{
public static void Start()
{
var engine = new PrecompiledMvcEngine2(typeof (RazorGeneratorMvcStart).Assembly)
{
UsePhysicalViewsIfNewer = true, //compile if file changed
PreemptPhysicalFiles = false //use local file if exist
};
ViewEngines.Engines.Add(engine);//Insert(0,engine) ignores local partial views
// StartPage lookups are done by WebPages.
VirtualPathFactoryManager.RegisterVirtualPathFactory(engine);
}
}
}
However there is maybe a small bug:
http://razorgenerator.codeplex.com/workitem/100
So for example in the code behind of a web form aspx page I would like to be able to do things like
string textBoxHtml = Html.TextBox("MyTextBox");
Is this possible?
Is the source code available to fork for webforms?
Possible? Yes.
The entire MVC source is available at:
http://www.microsoft.com/downloads/details.aspx?FamilyID=53289097-73ce-43bf-b6a6-35e00103cb4b&displaylang=en
Good luck!
You'll quickly find that pulling bits of code out of MVC is like only wanting a banana and getting the gorilla holding it. ;)
Here's something that is working for me so far.
public static class PageCommon
{
public static System.Web.Mvc.UrlHelper GetUrlHelper(this System.Web.UI.Control c)
{
var helper = new System.Web.Mvc.UrlHelper(c.Page.Request.RequestContext);
return helper;
}
class ViewDataBag : IViewDataContainer
{
ViewDataDictionary vdd = new ViewDataDictionary();
public ViewDataDictionary ViewData
{
get
{
return vdd;
}
set
{
vdd = value;
}
}
}
public static System.Web.Mvc.HtmlHelper GetHtmlHelper(this System.Web.UI.Control c)
{
IViewDataContainer x;
var v = new System.Web.Mvc.ViewContext();
var helper = new System.Web.Mvc.HtmlHelper(v, new ViewDataBag());
return helper;
}