ViewBag任意属性的实现方法

MVC中ViewBag可以设置任意自定义的属性，也可以读取出来。

如下面这样在controller的action方法中设置了ViewBag的一个Entires属性（该属性名字任意取）后，在相应的view中也可以读取出来，那这是怎样做到的呢？

 public ActionResult Index()
        {
           
          
            var mostrecentEntiries = (from m in dbContext.test orderby m.ID descending select m).Take(10);
            ViewBag.Entires = mostrecentEntiries;         
            return View();
        }

先来看ViewBag是个什么东西？ViewBag在ControllerBase类中的定义如下：

   [Dynamic]
    public object ViewBag
    {
        [return: Dynamic]
        get
        {
            Func<ViewDataDictionary> viewDataThunk = null;
            if (this._dynamicViewDataDictionary == null)
            {
                if (viewDataThunk == null)
                {
                    viewDataThunk = delegate {
                        return this.ViewData;
                    };
                }
                this._dynamicViewDataDictionary = new DynamicViewDataDictionary(viewDataThunk);
            }
            return this._dynamicViewDataDictionary;
        }
    }

看出来了，他其实是一个DynamicViewDataDictionary类型，而DynamicViewDataDictionary得类型定义又如下：

internal sealed class DynamicViewDataDictionary : DynamicObject
{
    // Fields
    private readonly Func<ViewDataDictionary> _viewDataThunk;

    // Methods
    public DynamicViewDataDictionary(Func<ViewDataDictionary> viewDataThunk)
    {
        this._viewDataThunk = viewDataThunk;
    }

    public override IEnumerable<string> GetDynamicMemberNames()
    {
        return this.ViewData.Keys;
    }

    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        result = this.ViewData[binder.Name];
        return true;
    }

    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        this.ViewData[binder.Name] = value;
        return true;
    }

    // Properties
    private ViewDataDictionary ViewData
    {
        get
        {
            return this._viewDataThunk();
        }
    }

 

关键就是实现了上述两个绿色的方法，我们自己也来模拟一个这样的效果看，只需自定义一个继承了DynamicObject的类并重写TrySetMember,TryGetMember两个方法即可实现ViewBag同样的效果：

 class myDynamic : DynamicObject
        {
            Dictionary<string, object> ViewData;
            public override bool TrySetMember(SetMemberBinder binder, object value)
            {
                this.ViewData[binder.Name] = value;
                return true;
            }
            public override object TryGetMember(GetMemberBinder binder, object value)
            {

                return this.ViewData[binder.Name];
            }
        }
        protected void Application_Start()
        {
            dynamic myDynamic = new myDynamic();
            myDynamic.Data = "aaa";
            string stra = myDynamic.Data;