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Question

I have Panel Object on my page , I want to replace it with another Panel

//Info.panel[cb_page_number.SelectedIndex] = pnl_page_active;
Panel new_panel = new Panel();
new_panel.BackColor = Color.White;
//new_panel.Name ="page_"+ (cb_page_number.SelectedIndex+1).ToString();
//cb_page_number.Items.Add(new_panel.Name);
//cb_page_number.SelectedIndex = cb_page_number.Items.Count-1;
pnl_page_active = new_panel;
pnl_page_active.Refresh();
pnl_page_active.Update();
Application.DoEvents();

pnl_page_active has a ivory background color,And there is some controls on that. When I execute above code I expext to see pnl_page_active background has been changed and there is no control on that,But it's the same,So I'm wondering what's the problem?

Answer 1

All you have done is assigning new_panel variable to pnl_page_active. It has nothing to do with Control hierarchy.

You need to remove the old panel from it's parent and insert the new one:

Control parent = pnl_page_active.Parent;
if (parent != null) {
    parent.Controls.Remove(pnl_page_active);
    parent.Controls.Add(new_panel);
}

Answer 2

What you're currently doing is modifying pnl_page_active to reference the same Panel that new_panel is... but new_panel was never added to the Form, so you don't see the color change.

Remove all the code you posted above, and just change the BackColor directly:

pnl_page_active.BackColor = Color.White;

If you want to replace the existing Panel with the new one (for whatever reason), you'll have to make sure it has the same parent, size, location, etc, in addition to whatever attributes you're copying.

Panel new_panel = new Panel();
new_panel.BackColor = Color.White;
new_panel.Size = pnl_page_active.Size;
new_panel.Location = pnl_page_active.Location;
new_panel.Parent = pnl_page_active.Parent;
new_panel.Show();

pnl_page_active.Hide();  // or Dispose if you don't want it anymore