Thread Safe Control - Crashing VS 2008

Question

Hello,

I am working on creating a thread safe control for my windows forms application.

I understand I can set the text on a control thread safe by using the following code:

private delegate void SetTextD(Control control, string value);

private static void SetText(Control control, string value)
{
    if(control.InvokeRequired)
    {
        control.Invoke(new SetTextD(SetText), new object[] {control, value});
    }
    else
    {
        control.Text = value;
    }
}

Then in my form code i can call:

SetText(lblStatus, "Updating...");

My goal is to create a custom control, which inherits Label. Then inside this class, on the Text property I can just call:

lblStatus.Text = "Updating..."

Then it will automatically do the proper thread safe code.

Here is the code that I have in my class:

public class ThreadSafeLabel : Label 
{
    private delegate string GetTextD();
    private delegate void SetTextD(string value);

    private string GetText()
    {
        if (InvokeRequired)
        {
            return (string)Invoke(new GetTextD(GetText));
        }
        return Text;
    }

    private void SetText(string value)
    {
        if(InvokeRequired)
        {
            Invoke(new SetTextD(SetText), new object[] {value});
        }
        else
        {
            Text = value;
        }
    }

    public override string Text
    {
        get
        {
            return GetText();
        }
        set
        {
            SetText(value);
        }
    }
}

Now, when I attempt to add this control to my form, it crashes VS 2008. I was thinking that maybe it had to do with setting the initial text property when you add it to the form, but not sure.

Any thoughts on what I might be doing wrong or what I might be missing?

If something is not clear, please ask.

Thanks!

Answer 1

Try a

return base.Text;

or you will run into a endless loop (when you add the Label to your Form the Text-property is queried - and the endless loop makes VS crash). Same for your setter.

Answer 2

Because of C# 3.0's anonymous methods, you don't need separate set and get methods. The simplest way to do what you're looking for is like this:

public class ThreadSafeLabel : Label {
    public override string Text {
        get {
            return InvokeRequired ? Invoke(new Func<string>(() => base.Text)) : base.Text;
        }
        set { 
            if (InvokeRequired)
                BeginInvoke(new Action(() => base.Text = value));
            else
                base.Text = value;
        }
}

Note that I'm using BeginInvoke so that the calling thread will not wait for the invoke to complete; you might want to change it to Invoke.

EDIT:

The problem with your code is that your set and get methods are calling your overridden Text property again, creating an infinte loop that results in a stack overlow (the exception, not the website). You need to write base.Text to call the base class' implementation of the Text property.