tpanel,C++ Builder中在TPanel上画图

由于TPanel没有Canvas属性，属于其自身维护了其绘制的功能，要在其上画图，需要重载它的WM_PAINT消息。
//.h文件 class TForm1 : public TForm { __published: // IDE-managed Components TPanel *Panel1; TButton *Button1; private: // User declarations TWndMethod FPanelWndProc; void __fastcall PanelWndProc(TMessage& Message); public: // User declarations __fastcall TForm1(TComponent* Owner); virtual __fastcall ~TForm1(); }; //,cpp文件 __fastcall TForm1::TForm1(TComponent* Owner) : TForm(Owner) { // remember the panel 's original window procedure FPanelWndProc = Panel1-> WindowProc; // subclass the panel Panel1-> WindowProc = PanelWndProc; } //--------------------------------------------------------------------------- __fastcall TForm1::~TForm1() { // restore the panel 's original window procedure Panel1-> WindowProc = FPanelWndProc; FPanelWndProc = NULL; } //--------------------------------------------------------------------------- void __fastcall TForm1::PanelWndProc(TMessage& Message) { FPanelWndProc(Message); // do your own painting if (Message.Msg == WM_PAINT) { // Graphics::TBitmap *bit = new Graphics::TBitmap; // bit->Assign(Image1->Picture->Graphic); // HDC hDC = GetDC(Panel1->Handle); // StretchBlt(hDC,0,0,Panel1->Width,Panel1->Height,bit->Canvas->Handle, // 0,0,bit->Width,bit->Height,SRCCOPY); // delete bit; float Step; TRect BandRect; //A panel doesn 't have a canvas property. Create _disibledevent=> Control=Panel1; Step=(float)Panel1-> ClientHeight/256; //256 bandes de couleur for(int i=0;i <256;i++) { BandRect.Left=0; BandRect.Top=(int)(i*Step); BandRect.Right=Panel1-> ClientWidth+1; BandRect.Bottom=(int)((i+1)*Step); // bandes horizontales PanelCanvas-> Brush-> Color=RGB(0,0,255-i); // bandes bleues PanelCanvas-> FillRect(BandRect); } delete PanelCanvas; } }

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