急等一个关于Canvas的有关问题

急等一个关于Canvas的问题～
pbBack-> Parent   =   Panel1;
                pbBack-> Canvas-> Pen-> Color   =   clRed;
                pbBack-> Canvas-> Brush-> Color   =   clBlue;
                pbBack-> Canvas-> Rectangle(0,0,Panel1-> ClientWidth,Panel1-> ClientHeight);
                pbBack-> Visible   =   true;
                pbBack-> BringToFront();

在一个窗体中，在FormCreate中放入的语句，结果我想要的矩形没有画出来～急求原因

注：pbBack是个TPaintBox对象

------解决方案--------------------
__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
pbBack-> Parent = Panel1;
pbBack-> Visible = true;
pbBack-> BringToFront();
}
//TPaintBox OnPaint
void __fastcall TForm1::pbBackPaint(TObject *Sender)
{

pbBack-> Canvas-> Pen-> Color = clRed;
pbBack-> Canvas-> Brush-> Color = clBlue;
pbBack-> Canvas-> Rectangle(0,0,Panel1-> ClientWidth,Panel1-> ClientHeight);
}