ViewData用于将数据从控制器传递给ViewData，它是从viewdatdictionary类派生出来的。仅对当前请求可用。仅要求复杂数据类型的类型转换，并检查null值以避免错误。如果发生重定向，则其值为null

ViewBag是一个动态属性，它利用了c# 4.0中的新动态特性。它也仅对当前请求可用。如果发生重定向，则其值为null

它使用c# 4.0动态特性。它实现了与viewdata相同的目标，应该避免使用强类型视图模型(与viewdata应该避免的方式相同)。

基本上它取代了魔法字符串:

ViewData["Foo"]

具有神奇属性:

ViewBag.Foo

你没有编译时安全性。

我继续指责微软在MVC中引入了这个概念。

属性的名称区分大小写。

有一些细微的区别，这意味着你可以使用ViewData和ViewBag与视图略有不同的方式。这篇文章http://weblogs.asp.net/hajan/archive/2010/12/11/viewbag-dynamic-in-asp-net-mvc-3-rc-2.aspx中概述了一个优点，并展示了在示例中可以通过使用ViewBag而不是ViewData来避免强制转换。

Although you might not have a technical advantage to choosing one format over the other, you should be aware of some important differences between the two syntaxes. One obvious difference is that ViewBag works only when the key you’re accessing is a valid C# identifi er. For example, if you place a value in ViewData["Key With Spaces"], you can’t access that value using ViewBag because the code won’t compile. Another key issue to consider is that you cannot pass in dynamic values as parameters to extension methods. The C# compiler must know the real type of every parameter at compile time in order to choose the correct extension method. If any parameter is dynamic, compilation will fail. For example, this code will always fail: @Html.TextBox("name", ViewBag.Name). To work around this, either use ViewData["Name"] or cast the va

在ViewBag内部，属性以名称/值对的形式存储在ViewData字典中。

注意:在MVC 3的大多数预发布版本中，ViewBag属性被命名为ViewModel，这段代码来自MVC 3发布说明:

有人建议我发布我发布的这个信息的来源，下面是来源: http://www.asp.net/whitepapers/mvc3-release-notes#_Toc2_4

MVC 2 controllers support a ViewData property that enables you to pass data to a view template using a late-bound dictionary API. In MVC 3, you can also use somewhat simpler syntax with the ViewBag property to accomplish the same purpose. For example, instead of writing ViewData["Message"]="text", you can write ViewBag.Message="text". You do not need to define any strongly-typed classes to use the ViewBag property. Because it is a dynamic property, you can instead just get or set properties and it will resolve them dynamically at run time. Internally, ViewBag properties are stored as name/value pairs in the ViewData dictionary. (Note: in most pre-release versions of MVC 3, the ViewBag property was named the ViewModel property.)

我能建议你不要用吗?

如果你想“发送”数据到你的屏幕上，发送一个强类型对象(又名ViewModel)，因为它更容易测试。

如果你绑定到某种类型的“模型”，并拥有随机的“viewbag”或“viewdata”项，那么这会使自动化测试变得非常困难。

如果您正在使用这些，请考虑如何重构并仅使用ViewModels。