Problem with delegate Syntax in C#

问题:

I built a Testbox to learn something about threading in windows form applications. Silverlight and Java are providing the Dispatcher, which really helps when updating GUI Elements.

Code Samples: Declaration Class Delegate

public delegate void d_SingleString(string newText);

Create Thread

        _thread_active = true;
        Thread myThread = new Thread(delegate() { BackGroundThread(); });
        myThread.Start();

Thread Function

    private void BackGroundThread()
    {
        while (_thread_active)
        {
            MyCounter++;
            UpdateTestBox(MyCounter.ToString());
            Thread.Sleep(1000);
        }
    }

Delegating TextBox Updates

    public void UpdateTestBox(string newText)
    {
        if (InvokeRequired)
        {
            BeginInvoke(new d_SingleString(UpdateTestBox), new object[] { newText });
            return;
        }
        tb_output.Text = newText;
    }

Is there a way to declare the Declaration of the Delate IN the BeginInvoke Method?!

something like

BeginInvoke(*DELEGATE DECLARATION HERE*, new object[] { newText });

Many thanks, rAyt

回答1:

In many cases like this, the simplest approach is to use a "captured variable" to pass state between the threads; this means you can keep the logic localised:

public void UpdateTestBox(string newText)
{
    BeginInvoke((MethodInvoker) delegate {
        tb_output.Text = newText;
    });        
}

The above is particularly useful if we expect it to be called on the worker thread (so little point checking InvokeRequired) - note that this is safe from either the UI or worker thread, and allows us to pass as much or as little state between the threads.

回答2:

For simple delegates like this you can use the Action<T> delegate (link to msdn) from the framework.

public void UpdateTestBox(string newText)
{
    if (InvokeRequired)
    {
        BeginInvoke(new Action<string>(UpdateTestBox), new object[] { newText });
        return;
    }
    tb_output.Text = newText;
}

That way you do not need to maintain your own delegate declarations.