Store two mouse click positions on canvas when checkbox enabled

I have a checkbox at the moment where, when I click it, it should allow the user to click two places on a canvas, and then a messagebox with the coordinates of both clicks appear, and then the checkbox should uncheck itself. I've tried various things and keep running into a few problems.

1. Checking the box is a RoutedEventArgs where as clicking on the canvas is a MouseButtonEventArgs.


2. I'm unable to store the second mouse click (the first click appears twice); I've tried various for loops, while loops, etc.


3. I'm unable to get the box to uncheck itself after the message box appears, regardless of where I put the .Checked == false. I get an error that says system.windows.etcetc.checked can only appaer on the left hand side of += or -=.

I'd like to handle the whole thing in a function related to the checkbox aka the routedeventargs and not a canvas click method.

I can figure out #2 but 1 and 3 have me stumped.

This is a sample of the method which is subscribed to from a canvas mousedown in the xaml:

   public void get_Scaling(object sender, MouseButtonEventArgs e)
    {
        Point startPoint;
        Point endPoint;

        while (Scale_btn.IsChecked == true)
        {
            startPoint = e.GetPosition(canvas1);

            endPoint = e.GetPosition(canvas1);

            System.Windows.MessageBox.Show("Start point is" + startPoint + "and end point is" + endPoint, "test", MessageBoxButton.OK, MessageBoxImage.Information);
        }
    }