asp.net-mvc – 从MVC中的控制器确定部分视图的模型

我原型化了一个可能的解决方案，因为它似乎是一个有趣的问题。我希望对你有用。

楷模

一，模型。我决定创建两个“小工具”，一个是新闻，一个是时钟。

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;
    }
}

调节器

我的控制器不了解任何意??见。它所做的是返回单个模型，但是该模型可以根据视图的要求动态获取正确的模型。

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);
}

使用代表，以便仅在实际使用正确的模型时创建/提取正确的模型。

ModelSelector

控制器使用的ModelSelector非常简单 – 只需保留一个代理包来创建每个模型类型：

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]();
    }
}

视图 – 简单的解决方案

现在，实现视图的最简单方法是：

@model MvcApplication2.ModelSelector
@using MvcApplication2.Models
@{
    var clock = (ClockModel) Model.GetModel(typeof (ClockModel));
}

<h2>The time is: @clock.Now</h2>

你可以在这里结束并使用这种方法。

意见 – 更好的解决方案

这很丑陋我希望我的意见如下：

@model MvcApplication2.Models.ClockModel
<h2>Clock</h2>
@Model.Now

和

@model MvcApplication2.Models.NewsModel
<h2>News Widget</h2>
@foreach (var headline in Model.Headlines)
{
    <h3>@headline</h3>
}

为了使这项工作，我不得不创建一个自定义视图引擎。

自定义视图引擎

当Razor视图被编译时，它会继承ViewPage< T>，其中T是@model。所以我们可以使用反射来确定视图想要什么类型，然后选择它。

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);
        }
    }
}

视图引擎注册在Global.asax.cs中：

ViewEngines.Engines.Clear();
ViewEngines.Engines.Add(new ModelSelectorEnabledRazorViewEngine());

渲染

我的家庭视图包括以下几行来测试它：

@Html.Action("Show","Widget",new { widgetName = "Clock" })
@Html.Action("Show",new { widgetName = "News" })