Panel in winform behaving wrongly

Question

I am having a panel in Winforms which loads panels in it during a method call. In the method call I have written following code:

//to get number of panel present in main panel so that new panel position can be set
int counT = panel1.Controls.Count;

Panel p = new Panel();
p.Location = new Point(3, 3 + (counT * 197));
p.Size = new Size(280, 150);

//To add panel to parent panel
panel1.Controls.Add(p);

Every time I call the method it will load a panel in the main panel. Everything works fine if i didn't scroll the scroll bar. Once I scroll the Scroll bar to down and after that i call the method, the distance between panels increases.

As per logic written the distance between two panel should be 197 pixel along Y axis, but it is increasing by more.

I have set AutoScroll=true

Any help !!!

Answer 1

That's quite strange behavior which I didn't know until now (and I have a lot experience in WF). It can be seen when the parent panel is scrolled when the code above is executed. I was thinking that child control positions are relative to the ClientRectangle , but it turns out that they are accounting the DisplayRectangle .

Shortly, instead of this

p.Location = new Point(3, 3 + (counT * 197));

use this

var parentRect = panel1.DisplayRectangle;
p.Location = new Point(parentRect.X + 3, parentRect.Y + 3 + (counT * 197));  

Answer 2

Panel.AutoScrollPosition affects Location property of all child controls. Scrolling works in this way. So you should keep in mind that, for example you could store current scroll position, move position to (0,0), add new controls, and restore scroll position after all

//to get number of panel present in main panel so that new panel position can be set
int counT = panel1.Controls.Count;
var pos = this.panel1.AutoScrollPosition; // Whe are storing scroll position
this.panel1.AutoScrollPosition = new Point(Size.Empty);
Panel p = new Panel();
p.Location = new Point(3, 3 + (counT * 197));
p.Size = new Size(280, 150);
p.BorderStyle = BorderStyle.FixedSingle;


//To add panel to parent panel
panel1.Controls.Add(p);
this.panel1.AutoScrollPosition = new Point(Math.Abs(pos.X), Math.Abs(pos.Y)); // We are restoring scroll position