Best practice: when to post back to UI

I have a question about the best paktik. When is the best time to send a callback to the UI when using the loading helper method like below? Button1 uses the Dispatcher on return, and Button2 allows the helper load class to encapsulate the dispatcher call. I prefer Button2.

private void Button1_Click(object sender, RoutedEventArgs e)
{
    AsyncLoader.LoadAsyncWithoutDispatcher(delegate(string result)
    {
        this.Dispatcher.Invoke((Action)delegate { this.TextBox1.Text = result; });
    });
}

private void Button2_Click(object sender, RoutedEventArgs e)
{
    AsyncLoader.LoadAsyncWithDispatcher(this.Dispatcher, delegate(string result)
    {
        this.TextBox1.Text = result;
    });
}

class AsyncLoader
{
    public static void LoadAsyncWithoutDispatcher(Action<string> completed)
    {
        var worker = new AsyncClass();
        worker.BeginDoWork(delegate(IAsyncResult result)
        {
            string returnValue = worker.EndDoWork(result);
            completed(returnValue);
        }, null);
    }

    public static void LoadAsyncWithDispatcher(Dispatcher dispatcher, Action<string> completed)
    {
        var worker = new AsyncClass();
        worker.BeginDoWork(delegate(IAsyncResult result)
        {
            string returnValue = worker.EndDoWork(result);
            dispatcher.Invoke(completed, returnValue);
        }, null);
    }
}