C# 繪製表單客戶非客戶區要用WM_PAINT和WM_NCPAINT

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表單分為兩部分：客戶區(Client area)和非客戶區(Non-Client area) 
WM_PAINT訊息、OnPaint()方法、GetDC()API函數都是處理表單客戶區繪製的 
  
而標題列處於非客戶區中，所以WM_PAINT訊息、OnPaint()方法、GetDC()API函數都用不上 
  
GetWindowDC()是獲得整個表單的畫布控制代碼(Device Context翻譯為：裝置清單，我習慣稱為畫布控制代碼)，包括非客戶區 
  
GDI的繪製都離不開DC，因為作業系統必須知道你要在什麼地方繪製圖形 
  
當其他表單遮擋或者移開，系統都會重新繪製表單。這時就會發出WM_PAINT和WM_NCPAINT訊息通知表單重繪介面。 
  
收到WM_NCPAINT訊息(非客戶區繪製訊息)說明非客戶區正需要重新繪製 
  
重載WndProc()方法(表單訊息處理過程)，處理WM_NCPAINT等訊息即可.... 
  
“基本的步驟” 就是：截獲WM_NCPAINT訊息、得到表單完整畫布控制代碼、在完整畫布上繪製圖形。 
    WM_NCPAINT WM_NCCALCSIZE WM_NCACTIVATE WM_NCHITTEST
建議樓主搜尋關鍵詞：“C# WM_NCPAINT WndProc Graphics”得到更多的參考資料 
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[DllImport   ( "User32.dll ")]   private   static   extern   IntPtr   GetWindowDC(IntPtr   hwnd);   [DllImport   ( "User32.dll ")]   private   static   extern   int   ReleaseDC(IntPtr   hwnd,   IntPtr   hdc);   [DllImport   ( "Kernel32.dll ")]   private   static   extern   int   GetLastError();   //標題列按鈕的矩形地區。   Rectangle   m_rect   =   new   Rectangle(205,   6,   20,   20);   protected   override   void   WndProc(ref   Message   m)   {   base.WndProc(ref   m);   switch(m.Msg)   {   case   0x86://WM_NCACTIVATE   goto   case   0x85;   case   0x85://WM_NCPAINT   {   IntPtr   hDC   =   GetWindowDC(m.HWnd);   //把DC轉換為.NET的Graphics就可以很方便地使用Framework提供的繪圖功能了   Graphics   gs   =   Graphics.FromHdc(hDC);   gs.FillRectangle(new   LinearGradientBrush(m_rect,   Color.Pink,   Color.Purple,   LinearGradientMode.BackwardDiagonal),   m_rect);   StringFormat   strFmt   =   new   StringFormat();   strFmt.Alignment   =   StringAlignment.Center;   strFmt.LineAlignment   =   StringAlignment.Center;   gs.DrawString( "√ ",   this.Font,   Brushes.BlanchedAlmond,   m_rect,   strFmt);   gs.Dispose();   //釋放GDI資源   ReleaseDC(m.HWnd,   hDC);   break;   }   case   0xA1://WM_NCLBUTTONDOWN   {   Point   mousePoint   =   new   Point((int)m.LParam);   mousePoint.Offset(-this.Left,   -this.Top);   if(m_rect.Contains(mousePoint))   {   MessageBox.Show( "hello ");   }   break;   }   }   }   //在視窗大小改變時及時更新按鈕的地區。   private   void   Form1_SizeChanged(object   sender,   System.EventArgs   e)   {   m_rect.X   =   this.Bounds.Width   -   95;   m_rect.Y   =   6;   m_rect.Width   =   m_rect.Height   =   20;   }   }   }