Say I have 5 buttons on a page, numbered 1-5.
When one is clicked, a value with a viewtate getter/setter assigns this the value of the button clicked.
If I am checking for a value in Page_Init() / OnInit(), after the postback has occured, the value will always be empty/null.
Is this correct?
If so, is there anything else I can do that doesnt require an architectural change? Or something similar I can use to persist changes across post backs (Session[] no good unfortunately).
ViewState stores the state of the page (page and control settings + custom values stored in ViewState) between post backs. It is just hidden field with serialized (and encrypted) state data. When you set something to ViewState in code behind it is transfered with page markup to the client and posted back to the sever in the next Postback. The page life cycle (between InitComplete and PreLoad) deserializes state from ViewState. That is the reason why you can't access data from ViewState in OnInit.
refer to :http://code.google.com/p/citiport2/wiki/All_Events
Page: AddParsedSubObject
Page: CreateControlCollection
Page: AddedControl
Page: AddParsedSubObject
Page: AddedControl
Page: ResolveAdapter
Page: DeterminePostBackMode
Page: PreInit
Control: ResolveAdapter
Control: Init
Control: TrackViewState
Page: Init
Page: TrackViewState
Page: InitComplete
Page: LoadPageStateFromPersistenceMedium
Control: LoadViewState
Page: EnsureChildControls
Page: CreateChildControls
Page: PreLoad
Page: Load
Control: DataBind
Control: Load
Page: EnsureChildControls
Page: LoadComplete
Page: EnsureChildControls
Page: PreRender
Control: EnsureChildControls
Control: PreRender
Page: PreRenderComplete
Page: SaveViewState
Control: SaveViewState
Page: SaveViewState
Control: SaveViewState
Page: SavePageStateToPersistenceMedium
Page: SaveStateComplete
Page: CreateHtmlTextWriter
Page: RenderControl
Page: Render
Page: RenderChildren
Control: RenderControl
Page: VerifyRenderingInServerForm
Page: CreateHtmlTextWriter
Control: Unload
Control: Dispose
Page: Unload
Page: Dispose
Page: Init is earlier
I'm not 100% sure what you're asking here, but it sounds like a problem with the ASP.NET Page Lifecycle. It trips up everyone!
Basically, what happens is that a developer expects to be able to do some work in Page_Init (or more commonly Page_Load), but the click event for whatever triggered the postback hasn't happened yet.
In fact, iirc ViewState hasn't even been deserialized when Page_Init fires.
I can't tell you where the right place to do whatever work needs done is without knowing more, but you probably want to move some of that code that's in Page_Init into an event handler later in the lifecycle.
You can see this for yourself: Pop a breakpoint at the start of Page_Init, and another one at the start of MyButton_Click, you'll see that Page_Init fires first.
You can use Request.Form["idofbutton"] to get the posted value. This happens as part of the http protocol. Inspect the http request/ response in something like firebug to see what is getting posted.