在父表单面板中显示用户控件

Question

The first line is able to clear the panel but doesnt seem to show the usercontrol in the panel in the parent form.

panel1.Parent.Controls.Clear();

if (panel1.Parent == null)
    return;

messagessent uc = new messagessent();
uc.Dock = DockStyle.Fill;
panel1.Parent.Controls.Add(uc);

Answer 1

Why you use panel1.Parent ? In this way, you remove all controls not from the panel itself, but from the parent control on which this panel is located.

This action removes the panel itself. And, accordingly, the panel does not have a parent now. The Parent property becomes null .

I suppose you need to write like this:

panel1.Controls.Clear();

messagessent uc = new messagessent();
uc.Dock = DockStyle.Fill;
panel1.Controls.Add(uc);