C# – Nested Masterpages and .FindControl

asp.netcfindcontrolmaster-pages

On one site, I'm only using a single level Masterpage and in a page using that master, I can do this.Master.FindControl("controlName") to access the control. Works fine.

However, using the same code on a site with two masterpage levels. MainMaster and SpecificMaster which has MainMaster as its Master.

So on the page which uses SpecificMaster, FindControl is returning null for the object. The only difference I'm seeing is the nesting of the masterpages.

When I set breakpoint and look at page.Master, it's showing SpecificMaster and SpecificMaster is showing MainMaster as its master correctly, but FindControl is still failing.

When I view source in IE, the control is correctly named, no .NET munging going on.

Any thoughts here?

TIA!

Best Answer

When you're nesting master pages, you'll get an extra container "Content" you need to look through.

As a result, if you're trying to use FindControl from a given child page the usual approach is something to the effect of:

Label myLabel = (Label)this.Master.FindControl("myLabel");
myLabel.Text = "Success!";

Since we have a nested master page, with "myLabel" in the child master, this control will be contained within a content control.

So, this changes the code to:

ContentPlaceHolder ph = (ContentPlaceHolder)this.Master.Master.FindControl("yourContentPane");

Label myLabel = (Label)ph.FindControl("myLabel");
myLabel.Text = "Success!";

and in VB.NET

Dim ph As ContentPlaceHolder = DirectCast(Me.Master.Master.FindControl("yourContentPane"), ContentPlaceHolder)

Dim myLabel As Label = DirectCast(ph.FindControl("myLabel"), Label)
myLabel.Text = "Success!"

The content from the child page is loaded into the first master page control, which is subsequently loaded into the grandparent master page.

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on

As per Prerak K's update comment (since deleted):

I guess I have not presented the question properly.

Situation is this: I want to load data into a global variable based on the value of a control. I don't want to change the value of a control from the child thread. I'm not going to do it ever from a child thread.

So only accessing the value so that corresponding data can be fetched from the database.

The solution you want then should look like:

UserContrl1_LOadDataMethod()
{
    string name = "";
    if(textbox1.InvokeRequired)
    {
        textbox1.Invoke(new MethodInvoker(delegate { name = textbox1.text; }));
    }
    if(name == "MyName")
    {
        // do whatever
    }
}

Do your serious processing in the separate thread before you attempt to switch back to the control's thread. For example:

UserContrl1_LOadDataMethod()
{
    if(textbox1.text=="MyName") //<<======Now it wont give exception**
    {
        //Load data correspondin to "MyName"
        //Populate a globale variable List<string> which will be
        //bound to grid at some later stage
        if(InvokeRequired)
        {
            // after we've done all the processing, 
            this.Invoke(new MethodInvoker(delegate {
                // load the control with the appropriate data
            }));
            return;
        }
    }
}

Best Answer

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This is the style that Microsoft tends to use in their examples.

C# – Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on

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