Why is SaveViewState called twice in the Control Life Cycle?

[Stephen Miller]

Hi,

I'm just looking at the web control life cycle and it appears that the
SaveViewState method SaveViewState is called twice.

To demonstrate, I overrode each method of the Web Control Life Cycle
with a 'Page.Trace' command (note that the string '-> SaveViewState'
appears only once):

// 2: Object Initialization
protected override void OnInit(EventArgs e) {
Page.Trace.Write (" -> OnInit");
base.OnInit(e);
if (Page != null){
Page.RegisterRequiresPostBack(this);
}
}

// 3: Begin Tracking View State
protected override void TrackViewState () {
Page.Trace.Write (" -> TrackViewState");
base.TrackViewState();
}

// 3a: Postback -> LoadViewState
protected override void LoadViewState(Object viewState) {
Page.Trace.Write (" -> LoadViewState");
if (viewState == null) {
base.LoadViewState(viewState);
}
}

// 4: Load
protected override void OnLoad (EventArgs e) {
Page.Trace.Write (" -> OnLoad");
base.OnLoad(e);
}

// 5: PreRender
protected override void OnPreRender (EventArgs e) {
Page.Trace.Write (" -> OnPreRender");
base.OnPreRender(e);
}

// 6: Save View State
protected override object SaveViewState () {
Page.Trace.Write (" -> SaveViewState");
return base.SaveViewState();
}

// 7: Render
protected override void RenderContents(HtmlTextWriter writer){
Page.Trace.Write (" -> RenderContents");
writer.Write ("my test control");
}

// 9: Dispose
public override void Dispose(){
Page.Trace.Write (" -> Dispose");
base.Dispose();
}

I then compiled my control and added to a new WebForm and enabled
tracing in the page directive ('<%@ Page Trace=true ...'). The Trace
Information for the page indicates that my overridden SaveViewState
method was called twice, immediately before and after the 'Begin
SaveViewState' section:

Begin Init
-> OnInit
-> TrackViewState
End Init
-> OnLoad
Begin PreRender
-> OnPreRender
End PreRender
-> SaveViewState
Begin SaveViewState
-> SaveViewState
End SaveViewState
Begin Render
-> RenderContents
End Render

Is this expected? If so what does it mean?

Thanks,

Stephen

 

[Teemu Keiski]

Hi,

you are using tracing when you see this, right? The duplicate call occurs
only when you use tracing because page makes additional call to estimate the
size of view state.