C# WPF RenderTransform resets on mousedown

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C#

WPF

translate

transform

I am having a problem with this code. When I start the program the rectangle (Ruler) is in the center of the page. When I mousemove when MouseDown is true, the Rectangle (Ruler) is dragable as I want. However, this only works on the first drag. The next time I go to drag it the Ruler jumps back to it's original position, then when you mouse over it the distance from where it was to where it jumped back is calculated and it jumps off the screen as the mouseup event doesn't fire as the rectangle has moved. I basically want to be able to drag the object around the screen however many times I want, but the XStart and YStart need to take the new rendered values on each click.

I think the reason has to do with the e.GetPosition(this).X; as 'this' refers to the Grid that is the rulers parent.

From digging around I notice that When I click on it first XStart and YStart are equal to grid positions X and Y as expected, this is subtracted from the mouse move position to create an offset. The second time I click the behavior is exactly the same, however, it jumps back to the center. My guess is on the first click it makes a transformation but doesn't commit it to memory maybe, then on the second click rather than translating its current position I believe it might be translating the original values again.

Is it possible the margins or centering could be causing it?

Do I need to commit the RenderTransform to the program? or is there an error in my logic?

It would honestly make more sense if it didn't work at all, but to work perfectly once, then screw up makes no sense.

Here is the code:

private void Rectangle_MouseDown(object sender, MouseButtonEventArgs e)
{
    XStart = e.GetPosition(this).X;
    YStart = e.GetPosition(this).Y;

    Console.WriteLine("X: " + XStart + ", Y: " + YStart);

    MouseDown = true;

}

private void Rectangle_MouseMove(object sender, MouseEventArgs e)
{

    if(MouseDown)
    {
        X = e.GetPosition(this).X - XStart;
        Y = e.GetPosition(this).Y - YStart;

        Ruler.RenderTransform = new TranslateTransform(X, Y);
    }
}

private void Ruler_MouseUp(object sender, MouseButtonEventArgs e)
{
    MouseDown = false;
}