Automating the InvokeRequired code pattern

Lee’s approach can be simplified further

public static void InvokeIfRequired(this Control control, MethodInvoker action)
{
    // See Update 2 for edits Mike de Klerk suggests to insert here.

    if (control.InvokeRequired) {
        control.Invoke(action);
    } else {
        action();
    }
}

And can be called like this

richEditControl1.InvokeIfRequired(() =>
{
    // Do anything you want with the control here
    richEditControl1.RtfText = value;
    RtfHelpers.AddMissingStyles(richEditControl1);
});

There is no need to pass the control as parameter to the delegate. C# automatically creates a closure.

If you must return a value, you can use this implementation:

private static T InvokeIfRequiredReturn<T>(this Control control, Func<T> function)
{
    if (control.InvokeRequired) {
        return (T)control.Invoke(function);
    } else {
        return function();
    }
}

---

UPDATE:

According to several other posters Control can be generalized as ISynchronizeInvoke:

public static void InvokeIfRequired(this ISynchronizeInvoke obj,
                                         MethodInvoker action)
{
    if (obj.InvokeRequired) {
        var args = new object[0];
        obj.Invoke(action, args);
    } else {
        action();
    }
}

DonBoitnott pointed out that unlike Control the ISynchronizeInvoke interface requires an object array for the Invoke method as parameter list for the action.

---

UPDATE 2

Edits suggested by Mike de Klerk (see comment in 1st code snippet for insert point):

// When the form, thus the control, isn't visible yet, InvokeRequired  returns false,
// resulting still in a cross-thread exception.
while (!control.Visible)
{
    System.Threading.Thread.Sleep(50);
}

See ToolmakerSteve’s and nawfal’s comments below for concerns about this suggestion.