views:

4096

answers:

5

Hi

Is there any way to retrieve a control's position in a form, when the control may be inside other controls (like Panels)?

The control's Left and Top properties gives me only it's position within it's parent control, but what if my control is inside five nested panels, and I need it's position on the form?

Quick example:

The button btnA is located on coordinates (10,10) inside the panel pnlB.
The panel pnlB is located on coordinates (15,15) inside the form frmC.

I want btnA's location on frmC, which is (25,25).

Can I get this location?

+3  A: 

You could walk up through the parents, noting their position within their parent, until you arrive at the Form.

Edit: Something like (untested):

public Point GetPositionInForm(Control ctrl)
{
   Point p = ctrl.Location;
   Control parent = ctrl.Parent;
   while (! (parent is Form))
   {
      p.Offset(parent.Location.X, parent.Location.Y);
      parent = parent.Parent;
   }
   return p;
}
Hans Kesting
arrggg... beat me to it :)
armannvg
Yea, I thought of that, but it seemed like a impractical way to do it, so I was hoping there was another way. If no one has any other suggestion, that's what I will do.
Erlend D.
This is the way to do it, with a simple recursive function.
MusiGenesis
+5  A: 

You can use the controls PointToScreen method to get the absolute position with respect to the screen.

You can do the Forms PointToScreen method, and with basic math, get the controls position.

Raj More
Yes, thank you. Perfect!
Erlend D.
That's not going to work exactly right, unless you take into account the height of the titlebar and the width of the form's border.
MusiGenesis
How does this help for getting the control's absolute position? You have to pass in a Point object to PointToScreen(), which doesn't make sense in this case.
Tim
+5  A: 

I usually combine PointToScreen and PointToClient:

Point locationOnForm = control.FindForm().PointToClient(
    control.Parent.PointToScreen(control.Location));
Fredrik Mörk
+1  A: 

In my testing, both Hans Kesting's and Fredrik Mörk's solutions gave the same answer. But:

I found an interesting discrepancy in the answer using the methods of Raj More and Hans Kesting, and thought I'd share. Thanks to both though for their help; I can't believe such a method is not built into the framework.

Please note that Raj didn't write code and therefore my implementation could be different than he meant.

The difference I found was that the method from Raj More would often be two pixels greater (in both X and Y) than the method from Hans Kesting. I have not yet determined why this occurs. I'm pretty sure it has something to do with the fact that there seems to be a two-pixel border around the contents of a Windows form (as in, inside the form's outermost borders). In my testing, which was certainly not exhaustive to any extent, I've only come across it on controls that were nested. However, not all nested controls exhibit it. For example, I have a TextBox inside a GroupBox which exhibits the discrepancy, but a Button inside the same GroupBox does not. I cannot explain why.

Note that when the answers are equivalent, they consider the point (0, 0) to be inside the content border I mentioned above. Therefore I believe I'll consider the solutions from Hans Kesting and Fredrik Mörk to be correct but don't think I'll trust the solution I've implemented of Raj More's.

I also wondered exactly what code Raj More would have written, since he gave an idea but didn't provide code. I didn't fully understand the PointToScreen() method until I read this post: http://social.msdn.microsoft.com/Forums/en-US/netfxcompact/thread/aa91d4d8-e106-48d1-8e8a-59579e14f495

Here's my method for testing. Note that 'Method 1' mentioned in the comments is slightly different than Hans Kesting's.

private Point GetLocationRelativeToForm(Control c)
{
  // Method 1: walk up the control tree
  Point controlLocationRelativeToForm1 = new Point();
  Control currentControl = c;
  while (currentControl.Parent != null)
  {
    controlLocationRelativeToForm1.Offset(currentControl.Left, currentControl.Top);
    currentControl = currentControl.Parent;
  }

  // Method 2: determine absolute position on screen of control and form, and calculate difference
  Point controlScreenPoint = c.PointToScreen(Point.Empty);
  Point formScreenPoint = PointToScreen(Point.Empty);
  Point controlLocationRelativeToForm2 = controlScreenPoint - new Size(formScreenPoint);

  // Method 3: combine PointToScreen() and PointToClient()
  Point locationOnForm = c.FindForm().PointToClient(c.Parent.PointToScreen(c.Location));

  // Theoretically they should be the same
  Debug.Assert(controlLocationRelativeToForm1 == controlLocationRelativeToForm2);
  Debug.Assert(locationOnForm == controlLocationRelativeToForm1);
  Debug.Assert(locationOnForm == controlLocationRelativeToForm2);

  return controlLocationRelativeToForm1;
}
Tyler Collier
A: 

private Point FindLocation(Control ctrl) {

        if (ctrl.Parent is Form)
            return ctrl.Location;
        else
        {
            Point p = FindLocation(ctrl.Parent);
            p.X += ctrl.Location.X;
            p.Y += ctrl.Location.Y;
            return p;
        }
    }
sahin