How ViewBag in ASP NET MVC works

Question

How does the ASP NET MVC s ViewBag work  MSDN says it is just an Object  which intrigues me  how does  Magic  properties such as ViewBag Foo and magic strings ViewBag  Hello   actually work   Also  how can I make one and use it in my ASP NET WebForms app   Examples would be really appreciated

User · Answer

ViewBag is a dynamic type that allow you to dynamically set or get values and allow you to add any number of additional fields without a strongly-typed class They allow you to pass data from controller to view. In controller......

public ActionResult Index()
{
    ViewBag.victor = "My name is Victor";
    return View();
}

In view

@foreach(string a in ViewBag.victor)
{
     .........
}

What I have learnt is that both should have the save dynamic name property ie ViewBag.victor

User · Answer

public dynamic ViewBag       get               if   viewBag    null                         viewBag   new DynamicViewData      gt  ViewData                      return  viewBag

User · Answer

ViewBag is of type dynamic  More  you cannot do ViewBag  Foo    You will get exception - Cannot apply indexing with    to an expression of type  System Dynamic DynamicObject    Internal implementation of ViewBag actually stores Foo into ViewData  Foo    type of ViewDataDictionary   so those 2 are interchangeable  ViewData  Foo   and ViewBag Foo   And scope  ViewBag and ViewData are ment to pass data between Controller s Actions and View it renders

User · Answer

The ViewBag is an System Dynamic ExpandoObject as suggested  The properties in the ViewBag are essentially KeyValue pairs  where you access the value by the key  In this sense these are equivalent   ViewBag Foo    Bar   ViewBag  Foo      Bar

User · Answer

It s a dynamic object  meaning you can add properties to it in the controller  and read them later in the view  because you are essentially creating the object as you do  a feature of the dynamic type   See this MSDN article on dynamics   See  this article on it s usage in relation to MVC   If you wanted to use this for web forms  add a dynamic property to a base page class like so   public class BasePage   Page        public dynamic ViewBagProperty               get          set            Have all of your pages inherit from this   You should be able to  in your ASP NET markup  do    lt    ViewBagProperty X   gt    That should work   If not  there are ways to work around it

User · Answer

ViewBag is of type dynamic but  is internally an System Dynamic ExpandoObject    It is declared like this    dynamic ViewBag   new System Dynamic ExpandoObject     which is why you can do    ViewBag Foo    Bar    A Sample Expander Object Code   public class ExpanderObject   DynamicObject  IDynamicMetaObjectProvider       public Dictionary lt string  object gt  objectDictionary       public ExpanderObject                 objectDictionary   new Dictionary lt string  object gt               public override bool TryGetMember GetMemberBinder binder  out object result                object val          if  objectDictionary TryGetValue binder Name  out val                         result   val              return true                    result   null          return false             public override bool TrySetMember SetMemberBinder binder  object value                try                       objectDictionary binder Name    value              return true                    catch  Exception ex                        return false

User · Answer

ViewBag is used to pass data from Controller Action to view to render the data that being passed  Now you can pass data using between Controller Action and View either by using ViewBag or ViewData  ViewBag  It is type of Dynamic object  that means you can add new fields to viewbag dynamically and access these fields in the View  You need to initialize the object of viewbag at the time of creating new fields   e g  1  Creating ViewBag  ViewBag FirstName  John     Accessing View   ViewBag FirstName

[asp.net] How ViewBag in ASP.NET MVC works

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