TControl.Invalidate Method

Completely repaint control.

Pascal

procedure Invalidate; virtual;

C++

virtual __fastcall Invalidate();

Description

Use Invalidate when the entire control needs to be repainted. When more than one region within the control needs repainting, Invalidate will cause the entire window to be repainted in a single pass, avoiding flicker caused by redundant repaints. There is no performance penalty for calling Invalidate multiple times before the control is actually repainted.

C++ Examples:

Copy Code

/*
This example creates a region and selects this region as the
clipping rectangle for the Image component's canvas. It then
sets the canvas's brush color to red and calls FillRect 
using the ClipRect as the area to fill. Lastly, the ClipRect
is reset to the original value that it contained by calling
SelectClipRect with nil as the second parameter and deletes
the region.  Place a TImage object in the form.
*/
void __fastcall TForm1::Button1Click(TObject *Sender)
{
    HRGN MyRgn;

    MyRgn = ::CreateRectRgn(100,100,200,200);
    ::SelectClipRgn(Image1->Canvas->Handle,MyRgn);
    Image1->Canvas->Brush->Color = clRed;
    Image1->Canvas->FillRect(Image1->Canvas->ClipRect);
    Image1->Invalidate();
    ::SelectClipRgn(Image1->Canvas->Handle,NULL);
    ::DeleteObject(MyRgn);
}

Delphi Examples:

Copy Code

{
This example creates a region and selects this region as the
clipping rectangle for the Image component's canvas. It then
sets the canvas's brush color to red and calls FillRect 
using the ClipRect as the area to fill. Lastly, the ClipRect
is reset to the original value that it contained by calling
SelectClipRect with nil as the second parameter and deletes
the region.  Place a TImage object in the form.
}
procedure TForm1.Button1Click(Sender: TObject);
var
    MyRgn: HRGN;
begin
    MyRgn := CreateRectRgn(100,100,200,200);
    SelectClipRgn(Image1.Canvas.Handle,MyRgn);
    Image1.Canvas.Brush.Color := clRed;
    Image1.Canvas.FillRect(Image1.Canvas.ClipRect);
    Image1.Invalidate;
    SelectClipRgn(Image1.Canvas.Handle, HRGN(nil));
    DeleteObject(MyRgn);
end;