Month: January 2009

The problem

If you’re working on WinForms, you must know that you cannot call controls methods within a thread that is not the one that created those controls. To solve this problem, Microsoft recommend us to use the following code :

namespace TestWinForm
{
    public partial class MainForm : BaseForm
    {
        public MainForm()
        {
            InitializeComponent();
        }
        // a delegate that has been created specially for this method
        private delegate void DisplayDelegate(string text);

        // a method that may be called from a worker thread
        public virtual void Display(string text)
        {
            if (InvokeRequired)
            {
                Invoke(new DisplayDelegate(Display));
            }
            else
            {
                //the actual job is here
                textBox1.AppendText(text);
            }
        }
    }
}

This code is ugly because :

• you need to create a delegate for each single public method you can call from outside
• you need to put an “if/else” block in each method wich increase the complexity of your code

The trick

Here is a trick that could significantly reduce the amount of code needed to do the same job within a large project.

Within you base class

You probably have a common base class for all your UI components. Add this method :

namespace TestWinForm
{
    public class BaseForm : Form
    {
        // This allows a sub class to easily run a method within
        // an UI thread without the need of creating multiple 
        // delegate signatures for each method signatures
        protected virtual void ThreadSafe(MethodInvoker method)
        {
            if (InvokeRequired)
                Invoke(method);
            else
                method();
        }
    }
}

Within your UI classes

Now the only thing you need to do is to encapsulate the methode content with the ThreadSafe() method :

namespace TestWinForm
{
    public partial class MainForm : BaseForm
    {
        public MainForm()
        {
            InitializeComponent();
        }

        // public method that may be called from outside and within any
        // worker thread ...
        public virtual void Display(string text)
        {
            ThreadSafe(delegate
            {
                //do any UI related code here
                //note that because this is an anonym method, 
                //you can use the local parameter
                textBox1.AppendText(text);
            });
        }

Happy coding !