Control.Invoke with input Parameters

Question

From what I've found in C#, the Control.Invoke method requires that you use a delegate with no input parameters. Is there any way around this? I would like to invoke a method to update the UI from another thread and pass to string parameters to it.

Answer 1

Which version of C# are you using? If you are using C#3.5 you can use closures to avoid passing in parameters.

With C#3.5

public static class ControlExtensions
{
  public static TResult InvokeEx<TControl, TResult>(this TControl control,
                                             Func<TControl, TResult> func)
    where TControl : Control
  {
    return control.InvokeRequired
            ? (TResult)control.Invoke(func, control)
            : func(control);
  }

  public static void InvokeEx<TControl>(this TControl control,
                                        Action<TControl> func)
    where TControl : Control
  {
    control.InvokeEx(c => { func(c); return c; });
  }

  public static void InvokeEx<TControl>(this TControl control, Action action)
    where TControl : Control
  {
    control.InvokeEx(c => action());
  }
}

Safely invoking code now becomes trivial.

this.InvokeEx(f => f.label1.Text = "Hello World");
this.InvokeEx(f => this.label1.Text = GetLabelText("HELLO_WORLD", var1));
this.InvokeEx(() => this.label1.Text = DateTime.Now.ToString());

---

With C#2.0 it becomes less trivial

public class MyForm : Form
{
  private delegate void UpdateControlTextCallback(Control control, string text);
  public void UpdateControlText(Control control, string text)
  {
    if (control.InvokeRequired)
    {
      control.Invoke(new UpdateControlTextCallback(UpdateControlText), control, text);
    }
    else
    {
      control.Text = text;
    }
  }
}

Using it simple, but you have to define more callbacks for more parameters.

this.UpdateControlText(label1, "Hello world");

Answer 2

I think Samuel's (excellent) approach can be pushed even more:

Extension Method:

public static void ExecuteAsync<TControl>(this TControl control, Action action)
where TControl : Control
{
  new Thread(() =>
  {
    control.Invoke(action);
  })
  .Start();
}

Form code:

private void doStuff()
{
  this.ExecuteAsync(() =>
  {
    // Do your stuff in a separate thread
    // but having full access to local or instance variables.

    // No (visible) threading code needs to be used here.
  });
}

Answer 3

As Luke says, use Control.Invoke like this...

For example in a form:

public delegate void DelegatePassMessages(string name, int value);

public DelegatePassMessages passMessage;

In the contructor:

passMessage = new DelegatePassMessages (this.MessagesIn);

Then the MessagesIn function to receive data:

public void MessagesIn(string name, int value)
{

}

Then to pass data to your form:

formName.Invoke(formName.passMessage, new Object[] { param1, param2});