Justin Tanner Justin Tanner - 8 days ago 5
C# Question

Shortest way to write a thread-safe access method to a windows forms control

In this article:

http://msdn.microsoft.com/en-us/library/ms171728(VS.80).aspx

The author uses the following method to make thread-safe calls to a Windows Forms control:

private void SetText(string text)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (this.textBox1.InvokeRequired)
{
SetTextCallback d = new SetTextCallback(SetText);
this.Invoke(d, new object[] { text });
}
else
{
this.textBox1.Text = text;
}
}


Is there a shorter way to accomplish the same thing?

Answer

C# 3.0 and after:

An extension method would generally be the way to go, since you're always going to want to perform an action on an ISynchronizeInvoke interface implementation, it's a good design choice.

You can also take advantage of anonymous methods (closures) to account for the fact that you don't know what parameters to pass to the extension method; the closure will capture the state of everything needed.

// Extension method.
static void SynchronizedInvoke(this ISynchronizeInvoke sync, Action action)
{
    // If the invoke is not required, then invoke here and get out.
    if (!sync.InvokeRequired)
    {
        // Execute action.
        action();

        // Get out.
        return;
    }

    // Marshal to the required context.
    sync.Invoke(action, new object[] { });
}

You'd then call it like this:

private void SetText(string text)
{
    textBox1.SynchronizedInvoke(() => textBox1.Text = text);
}

Here, the closure is over the text parameter, that state is captured and passed as part of the Action delegate passed to the extension method.

Before C# 3.0:

You don't have the luxury of lambda expressions, but you can still generalize the code. It's pretty much the same, but not an extension method:

static void SynchronizedInvoke(ISynchronizeInvoke sync, Action action)
{
    // If the invoke is not required, then invoke here and get out.
    if (!sync.InvokeRequired)
    {
        // Execute action.
        action();

        // Get out.
        return;
    }

    // Marshal to the required context.
    sync.Invoke(action, new object[] { });
}

And then you call it with anonymous method syntax:

private void SetText(string text)
{
    SynchronizedInvoke(textBox1, delegate() { textBox1.Text = text; });
}