It's syntactic sugar, basically. I don't think it's meant to be functionally "better" than the old
ViewData dictionary, just a lot less verbose to work with. Instead of taking things out of the dictionary and manually casting them (and crashing if they're wrong), you can just use them without any extra verbiage (and crash if they're wrong).
Here is a blog post which has some "before and after" code samples using the old
ViewData dictionary and the new
ViewBag dynamic. In particular, see the
foreach iterating through the list of strings.
foreach (var color in ViewData["listColors"] as List<string>)
foreach (var color in ViewBag.ListColors)
Edit: Martinho makes an excellent point! The new version should probably explicitly declare a
string rather than a
var, like so:
foreach (string color in ViewBag.ListColors)
- If you've gotten it wrong, e.g.
ViewBag.ListColors is a
System.Drawing.Color objects, you'll get an immediate and clear error,
Cannot convert type 'System.Drawing.Color' to 'string', rather than weird and undesired output.
- If you declare
color as a
var, the type inference will infer it as a
dynamic, thus all the usage of it in the loop will go through the Dynamic Language Runtime's late binding, right? Surely this is an unnecessary performance hit?