Question

I’m working with a project that is WPF and VB.net. I want to visually simulate “dragging” an object (though I do not want to use standard drag and drop for reason of purpose).

Basically, I have a label object that, on its MouseDown event, I want it to follow the mouse cursor inside a 640×480 solid-size grid (but not outside of it!). Mind you, this grid is centered inside a full-screen window. Again, the object should not follow the mouse outside of the grid (I’m guessing a “ClipToBounds = True” here)

Then, on the label’s MouseUp event, I want it to either stay in its current position or return to its original position, as determined by the value of a boolean variable set by another object’s MouseEnter property.

Note, if it would be easier to work with, I can change the grid to a canvas in a cinch. I’m guessing that would be desirable.

So, after that long-winded explanation, here is my question (two-fold):

1. How do I make the object (label) follow the mouse cursor inside the grid/canvas, but not outside of it? This needs to happen on the MouseDown event of the label.

2. How do I make the object “stick” in its current position? (From this, I can probably figure out how to make it return to its original position on my own. 😀 )

My upvote to whoever can help me accomplish this goal the most efficiently! Thank you all very much.

Answer 1

How about something like this :

XAML :

<Canvas x:Name="canv" ToolTip="tt one" Width="400" Height="400" Background="Blue">
    <Rectangle x:Name="rec" Fill="Red" Height="50" Width="50" MouseDown="Rectangle_MouseDown" MouseMove="Rectangle_MouseMove" MouseUp="Rectangle_MouseUp" />
</Canvas>

CODE-BEHIND :

    private bool isDragging;
    private void Rectangle_MouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
    {
        rec.CaptureMouse();
        isDragging = true;

    }

    private void Rectangle_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
    {
        if (isDragging)
        {
            Point canvPosToWindow = canv.TransformToAncestor(this).Transform(new Point(0, 0));

            Rectangle r = sender as Rectangle;
            var upperlimit = canvPosToWindow.Y + (r.Height / 2);
            var lowerlimit = canvPosToWindow.Y + canv.ActualHeight - (r.Height / 2);

            var leftlimit = canvPosToWindow.X + (r.Width / 2);
            var rightlimit = canvPosToWindow.X + canv.ActualWidth - (r.Width / 2);


            var absmouseXpos = e.GetPosition(this).X;
            var absmouseYpos = e.GetPosition(this).Y;

            if ((absmouseXpos > leftlimit && absmouseXpos < rightlimit)
                && (absmouseYpos > upperlimit && absmouseYpos < lowerlimit))
            {
                Canvas.SetLeft(r, e.GetPosition(canv).X - (r.Width / 2));
                Canvas.SetTop(r, e.GetPosition(canv).Y - (r.Height / 2));
            }
        }
    }

    private void Rectangle_MouseUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
    {
        rec.ReleaseMouseCapture();
        isDragging = false;
    }

This code could be enhanced, but I think you got the idea 😉