添加Razor关键字

Question

What is the best process to extend the Razor view-engine to add additional keywords?

I'm not a fan of the dynamic ViewBag property, so for all of my pages I define both a strongly-typed ViewModel POCO, but also a strongly-typed ViewData object:

public abstract class BaseViewData<TModel,TController> : ViewDataDictionary<TModel>

( TController is specified to optionally allow strongly-typed callbacks to the parent Controller )

This is so I can have compile-time verified members, like String PageTitle (in a site-wide base class) and per-page members - it works in tandem with the ViewModel: the BaseViewData -subclass contains one-way data, and the ViewModel -class contains two-way data. This works great when you tweak the MSBuild system to precompile your views into the output assembly - no more .aspx or .cshtml files!

In ASP.NET MVC (using the WebForms view-engine) I have my own base ViewPage subclass:

public class ViewPage2<TViewModel,TViewData> : ViewPage<TModel> where TViewData : ViewDataDictionary<TModel> {

    private TViewData _data;

    public new TViewData ViewData {
        get {
            if( _data == null ) {
                _data = (TViewData)base.ViewData;
            }
            return _data;
        }
    }
}

I recently brought this over to Razor, easily done:

public abstract class WebViewPage2<TViewModel,TViewData> : WebViewPage<TModel> where TData : ViewDataDictionary<TModel> {
    // same ViewData property code as above
}

In the .cshtml files you can manually specify the base-class with the @inherits razor keyword - which requires the fully-qualified concrete generic type name - but alternatively you can omit @inherits and instead specify the @model keyword, which Razor will pass as the TModel argument to WebViewPage<TModel> .

As my base-class adds a second generic type argument, I'd rather not have to type out this ins my .cshtml files:

@inherits MyNamespace.WebViewPage2<MyOtherNameSpace.Views.FooViewModel,MyOtherNameSpace.Views.FooViewData>

...but instead do this:

Web.config

<system.web.webPages.razor>
    <pages pageBaseType="MyNamespace.WebViewPage2">
        ...

MyPage.cshtml

@model FooViewModel
@data FooViewData

But this would require extending the Razor View-engine somehow - but this is non-obvious as it requires extending the Razor parser itself so it recognises @data TViewData and passes it as the second type argument.

Answer 1

You can implement an inheriting ViewClass like this (be careful with the namespace, it must not be changed):

namespace System.Web.Mvc {
     public abstract class WebViewPage<TViewModel, TModel> : WebViewPage<TModel> where TViewModel : class {
         private TViewModel _viewModel;

         public TViewModel ViewModel {
             get {
                 if (_viewModel == null) {
                    throw new InvalidOperationException("No ViewModel defined for this View.");
                 }
                 return _viewModel;
             }
             set { _viewModel = value; }
         }

         public override void InitHelpers() {
              base.InitHelpers();

              if (this.ViewBag.ViewModel == null) {
                 // No ViewModel defined => set null.
              }
              else if (!(this.ViewBag.ViewModel is TViewModel)) {
                 throw new InvalidOperationException(string.Format("The specified ViewModel value is of type '{0}' and must be of type '{1}'.", this.ViewBag.ViewModel.GetType(), typeof(TViewModel)));
             } else {
                _viewModel = this.ViewBag.ViewModel;
             }
        }
    }
}

Then you dont have to change the web.config or anything else and can instantiate the view like this:

 @model ViewModelType, (Input?)ModelType

The typed ViewModel (Type would by ViewModelType) is then available in the view via @ViewModel . The Model of type (Input)ModelType is still available via @Model like it always was.