How can I use Razor model binding from a resource string? - asp.net-mvc

Question

Normally we have:
<div>
<div>Some property from a model: #Model.Property</div>
</div>
But let's say I have this exact line as a complete html line in a resource file and try to reference it:
<div>
#Resource.MyResourceLine
</div>
The model binding doesn't work. It renders the line raw without binding.
How can I make Razor bind in this scenario?
EDIT:
There's an alternative way that works by changing the content on the resource string to a string.Format placeholder:
<div>Some property from a model:{0}</div>
and then:
<div>
#string.Format(#Resource.MyResourceLine,#Model.Property)
</div>
But that makes it difficult to maintain large texts with many property references. It would be ideal if the property names could be seen in the resource file. Is there a more elegant way?

Answer 1

I did a bit of digging here and there in the source code for Asp.Net Mvc (latest version which is 5.2.3) taken from official codeplex: https://aspnetwebstack.codeplex.com/
Short answer:
There is no easy way for that out of the box, since the page is already compiled, and any string that you pass in your model is treated like a string - either MvcHtmlString or String. You may use RazorEngine package to do it fast and without lots of issues: (https://github.com/Antaris/RazorEngine)
Long answer:
When you open the route, and controller serves the view for it, you have to take parsed and compiled code for that view(which might get generated during startup, or lazily right before you actually use that view) and then render the page combining compiled View and your Model data (which is done when you call View() method in controller).
How ASP.NET parses and compiles the view, generating running code for it:
// https://aspnetwebstack.codeplex.com/SourceControl/latest#src/System.Web.Razor/RazorTemplateEngine.cs
// Line 152
protected internal virtual GeneratorResults GenerateCodeCore(ITextDocument input, string className, string rootNamespace, string sourceFileName, CancellationToken? cancelToken) {
//...
// Run the parser
RazorParser parser = CreateParser();
Debug.Assert(parser != null);
ParserResults results = parser.Parse(input);
// Generate code
RazorCodeGenerator generator = CreateCodeGenerator(className, rootNamespace, sourceFileName);
generator.DesignTimeMode = Host.DesignTimeMode;
generator.Visit(results);
//...
}
How asp.net renders the page, combining source code for view and data from the model
// https://aspnetwebstack.codeplex.com/SourceControl/latest#src/System.Web.WebPages/WebPageBase.cs
// Line 215
// public override void ExecutePageHierarchy() {
// ...
try
{
// Execute the developer-written code of the WebPage
Execute(); //**you can see example of the code it executes right below in the code block**
}
finally
{
TemplateStack.Pop(Context);
}
}
After the view is compiled, it's turned into a simple C# class that generates a string, that is then displayed to the user in browser. Let's create a simple Controller, View and ViewModel:
Here's some code:
ViewModel class:
namespace StackOverflow.Models
{
public class TestViewModel
{
public int IntProperty { get; set; }
public string StringProperty { get; set; }
}
}
Controller code:
public ActionResult Test()
{
var viewModel = new TestViewModel
{
IntProperty = 5,
StringProperty = "#DateTime.UtcNow.ToString()"
};
return View(viewModel);
}
View:
#model StackOverflow.Models.TestViewModel
#{
ViewBag.Title = "just a test";
Layout = null;
}
#Model.IntProperty
#Html.Raw(#Model.StringProperty)
An example of the page, using the code above, generates the following compiled view:
//------------------------------------------------------------------------------
// <auto-generated>
// This code was generated by a tool.
// Runtime Version:4.0.30319.42000
//
// Changes to this file may cause incorrect behavior and will be lost if
// the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------
namespace ASP {
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Web;
using System.Web.Helpers;
using System.Web.Security;
using System.Web.UI;
using System.Web.WebPages;
using System.Web.Mvc;
using System.Web.Mvc.Ajax;
using System.Web.Mvc.Html;
using System.Web.Optimization;
using System.Web.Routing;
using StackOverflow;
public class _Page_Views_Test_Index_cshtml : System.Web.Mvc.WebViewPage<StackOverflow.Models.TestViewModel> {
#line hidden
public _Page_Views_Test_Index_cshtml() {
}
protected ASP.global_asax ApplicationInstance {
get {
return ((ASP.global_asax)(Context.ApplicationInstance));
}
}
public override void Execute() {
#line 3 "XXX\Views\Test\Index.cshtml"
ViewBag.Title = "just a test";
Layout = null;
#line default
#line hidden
BeginContext("~/Views/Test/Index.cshtml", 100, 4, true);
WriteLiteral("\r\n\r\n");
EndContext("~/Views/Test/Index.cshtml", 100, 4, true);
BeginContext("~/Views/Test/Index.cshtml", 105, 17, false);
#line 8 "XXX\Views\Test\Index.cshtml"
Write(Model.IntProperty);
#line default
#line hidden
EndContext("~/Views/Test/Index.cshtml", 105, 17, false);
BeginContext("~/Views/Test/Index.cshtml", 122, 4, true);
WriteLiteral("\r\n\r\n");
EndContext("~/Views/Test/Index.cshtml", 122, 4, true);
BeginContext("~/Views/Test/Index.cshtml", 127, 31, false);
#line 10 "XXX\Views\Test\Index.cshtml"
Write(Html.Raw(#Model.StringProperty));
#line default
#line hidden
EndContext("~/Views/Test/Index.cshtml", 127, 31, false);
}
}
}
As you can see, your page code is just written to output section by section, checking Write method leads to these implementation details:
public override void Write(object value)
{
WriteTo(Output, value);
}
public static void WriteTo(TextWriter writer, object content)
{
writer.Write(HttpUtility.HtmlEncode(content)); //writer - instance of TextWriter
}
So anything that you put into your string field in the viewmodel is simply encoded with HtmlEncode method and put to the page, and it cannot be compiled in the run time with default usage of mvc features.
I am really sure, that you can do it with Mvc and Razor digging deep into the sources, but that will require a lot more time and probably a lot of good old hacks. For a fast and simple solution you can use https://github.com/Antaris/RazorEngine package. You can also check its source code for how they did this.
Here's controller code, that will rended a template using RazorEngine package:
public ActionResult Test()
{
var stringTemplate = #"
#model StackOverflow.Models.TestViewModel
<br/>
>>COMPILED
<br/>
#DateTime.UtcNow.ToString()
<br/>
Compiled model int property value:
<br/>
#Model.IntProperty
";
var viewModel = new TestViewModel
{
IntProperty = 5,
StringProperty = null
};
viewModel.StringProperty = Engine.Razor.RunCompile(stringTemplate, viewModel.GetType().ToString(), null, viewModel);
return View("Index", viewModel);
}
Basic idea here is pretty simple - pass the rendering to the component, do it in controller and pass the string you got to the ViewModel, then use #HtmlHelper.Raw to render HTML that you got from the engine.
This might work for a lot scenarios, but I would strongly recommend you not to do it unless you really need it and there are no viable alternatives. Dynamic razor templates are very hard to maintain.