Question

I am making an application using WPF and C#. What I’m trying to do is to print a lots of shapes on a canvas with some time in between when I push a button. At the moment when I push the button, everything just pops up at once. I have tried to sleep the thread for some time between every “print” but that doesn’t help, it just take longer time before everything splash up at once. What I want to achive is that the shapes pop up one at a time with lets say 0.5 seconds in between. The code is the following:

   private void Create_Click(object sender, RoutedEventArgs e)
   {
        Random random = new Random();
        for (int i = 0; i < 50; i++)
        {
            Thread.Sleep(500);
            Path f = FlowerFactory.createFlower(FlowerBP, true);
            Canvas.SetLeft(f, random.Next(0, 1650));
            Canvas.SetTop(f, random.Next(0,1000));
            DrawBoard.Children.Add(f);
        }}

Answer 1

You need to, first, run the loop in a background thread so that it doesn’t block the UI from updating; and second, send the UI-rendering tasks back to the UI thread. For the first, you can use Task.Factory.StartNew, and for the second, use Dispatcher.Invoke:

Random random = new Random();
Task.Factory.StartNew(() =>
{
    for (int i = 0; i < 50; i++)
    {
        Thread.Sleep(500);
        Dispatcher.Invoke(DispatcherPriority.Render, new Action(() =>
        {
            Path f = FlowerFactory.createFlower(FlowerBP, true);
            Canvas.SetLeft(f, random.Next(0, 1650));
            Canvas.SetTop(f, random.Next(0,1000));
            DrawBoard.Children.Add(f);
        }));
    }
});