How to change the Z order of WPF controls at runtime

It's as simple as this -- keep track of the highest zIndex and before assigning it to the control that needs to have the highest ZIndex - increment it, that way you ensure that the current control has the highest ZIndex and also if there is a set Z order, you are not going to mess it up.

The code would look something like this:

//set
var zIndex = ((YourCurrentControlType)sender).GetValue(Parent.ZIndexProperty);

//get
someControl.SetValue (Parent.ZIndexProperty, zIndex++);

In my previous post I wanted to move WPF controls at runtime on canvas by selecting them with the mouse and dragging them to a new location. The problem was that the dragged control, if overlapped the other control, would appear to be behind it, if its Z order was lower. So I needed to change the Z order of the control that is being dragged.


L O G I C

Current control should have the highest Z order, so introduce an variable that keeps track of the highest Z order and assigns it to the current control that needs it (incrementing it beforehand, to ensure that it has the highest one).

I M P L E M E N T A T I O N

I used the code from my previous post on how to move WPF controls and modified a couple of things:

1. Introduce the z Order variable by adding it as the ZIndex property to the public class Element

  private int zIndex = 0;
  public int ZIndex
  {
      get { return this.zIndex; }
      set { this.zIndex = value; }
  }

2. add a line of code to function rect1_MouseLeftButtonDown() to capture the current Z order:

private void rect1_MouseLeftButtonDown(object sender,
                                       MouseButtonEventArgs e)
{
   //capture the last highest z index 
   //before pointing to new current element
   int newZIndex = (int)((Border)sender).GetValue(Canvas.ZIndexProperty);
   this.current.ZIndex = newZIndex > this.current.ZIndex ?
                         newZIndex :
                         this.current.ZIndex;

   //capture the new current element
   this.current.InputElement = (IInputElement)sender;
}

3.Assign the highest Z order to the current control in Canvas_MouseMove:

private void Canvas_MouseMove(object sender, MouseEventArgs e)
{
   if ( e.LeftButton == MouseButtonState.Pressed &&
        current.InputElement != null)
   {
      //increment z-Order and pass it to the current element, 
      //so that it stays on top of all other elements
      ((Border)this.current.InputElement).SetValue(Canvas.ZIndexProperty,
                                                   this.current.ZIndex++);

      if (this.current.IsDragging)
         Drag(sender);//shortened, see how to drag in previous post
   }
}

And that's it...pretty simple.
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