Drag a point in a WPF diagram?

In WPF, points on a graph are not draggable by default. You must handle mouse events and update the point’s position manually.

Simple idea to make a point draggable in WPF:

1. Draw points using a Canvas (best for absolute positioning)

2. Capture mouse events (MouseDown, MouseMove, MouseUp)

3. Update the point’s Canvas.Left and Canvas.Top while dragging

Basic approach:

• On MouseDown ? start dragging

• On MouseMove ? change the point position

• On MouseUp ? stop dragging

Example (Ellipse as a draggable point):

bool isDragging = false;
Point mouseOffset;

private void Point_MouseDown(object sender, MouseButtonEventArgs e)
{
    isDragging = true;
    var ellipse = sender as Ellipse;
    mouseOffset = e.GetPosition(ellipse);
    ellipse.CaptureMouse();
}

private void Point_MouseMove(object sender, MouseEventArgs e)
{
    if (!isDragging) return;

    var ellipse = sender as Ellipse;
    var position = e.GetPosition(MyCanvas);

    Canvas.SetLeft(ellipse, position.X - mouseOffset.X);
    Canvas.SetTop(ellipse, position.Y - mouseOffset.Y);
}

private void Point_MouseUp(object sender, MouseButtonEventArgs e)
{
    isDragging = false;
    var ellipse = sender as Ellipse;
    ellipse.ReleaseMouseCapture();
}

points to remember:

• Use Canvas for graph plotting

• Each point (Ellipse) can be dragged independently

• Update coordinates to redraw lines if the graph is connected

This is the standard and recommended way to drag graph points in WPF.