User control instances are null while using nested master page

I have couple of user controls which are statically referenced in aspx. We are setting some public properties on the user controls in Page_Preinit event. The page also references a master page

This was working fine so far. Had to do a ui redesign and we implemented nested master pages.

Now, all of a sudden, 开发者_高级运维the user controls are showing up as null. If I change the master page to parent one (instead of child -nested), it works fine.

Appreciate any pointers to this issue.

some sample code: here ucAddress is null

protected void Page_PreInit(object sender, EventArgs e) { ucAddress.City = "Dallas"; }

This blog post describes the problem very well and also offers a solution. I can confirm that the solution works and I'll repeat the relevant parts here:

The problem

We have a user control and initialize its control in the Init event so that it is ready when the ViewState is restored (between Init and Load).

Once you start using this encapsulation technique, it won’t be long until you want to pass in a parameter that affects the data you load. Before we do, we need to be aware that the Init event is fired in reverse order. That is, the child controls have their Init event fired before that event is fired at the parent. As such, the Page.Init event is too late for us to set any properties on the controls.

The natural solution is to try and use the Page.PreInit event, however when you do you’ll often find that your control references are all null. This happens when your page is implemented using a master page, and it relates to how master pages are implemented. The <asp:ContentPlaceHolder /> controls in a master page use the ITemplate interface to build their contents. This content (child controls) is not usually prepared until the Init event is called, which means the control references are not available. For us, this represents a problem.

The Solution

The fix is remarkably simple; all we need to do is touch the Master property on our Page and it will cause the controls to become available. If we are using nested master pages, we need to touch each master page in the chain.

The author of the blog post then offers a nice little snippet that you can execute in the PreInit handler of your Page that uses a MasterPage and contains a user control:

protected override void OnPreInit(EventArgs e)
{
    // Walk up the master page chain and tickle the getter on each one
    MasterPage master = this.Master;
    while( master != null ) master = master.Master;
    
    // Access now initialized user control
    ucAddress.City = "Dallas";
}

Found the issue. had to initialize child master page before accessing user control.