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Determine the model of a partial view from the controller within MVC

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长情又很酷
长情又很酷 2020-12-13 10:12

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 pro

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  • 暖寄归人
    暖寄归人 (楼主)
    2020-12-13 10:55

    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(() => new ClockModel(DateTime.Now));
    selector.WhenRendering(() => 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> modelLookup = new Dictionary>();

    public void WhenRendering(Func 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));
}


    The time is: @clock.Now
    

    


    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

    Clock
    
@Model.Now

    


    And
    


    @model MvcApplication2.Models.NewsModel

    News Widget
    
@foreach (var headline in Model.Headlines)
{
    
    @headline
    
}

    


    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, 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, 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
                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" })

    
    
    
             
    
                                                        
    
            
            
    
              
                
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