清除時GDI +中的一般錯誤

Question

從API調用我的項目時，我得到了這個異常。

當我們改變某個值時，從事件調用throw消息的方法，它將重繪背景並重繪字符串。這通常在正常使用應用程序時不會發生，但是當我從API中更改值時，它有時會拋出此錯誤。

---

System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+. 
    at System.Drawing.Graphics.Clear(Color color) at MyCompany.Project.GUI.Drawable.DrawLabel() in D:\Source\MyCompany\Project\GUI\Drawable.cs:line 191 
    at MyCompany.Project.GUI.Drawable.OnPaint(PaintEventArgs e) in D:\Source\MyCompany\Project\GUI\Drawable.cs:line 26 
    at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer, Boolean disposeEventArgs) 
    at System.Windows.Forms.Control.WmPaint(Message& m) 
    at System.Windows.Forms.Control.WndProc(Message& m) 
    at System.Windows.Forms.ScrollableControl.WndProc(Message& m) 
    at System.Windows.Forms.ContainerControl.WndProc(Message& m) 
    at System.Windows.Forms.UserControl.WndProc(Message& m) 
    at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) 
    at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) 
    at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) 

---

這裏是我的代碼看起來像

public class Drawable : UserControl 
{ 
    private Graphics g; 
    public void OnPaint(PaintEventArgs e) 
    { 
     base.OnPaint(e); 
     DrawLabel(); 
    } 
    private void DrawLabel() 
    { 
     if ((TopLabels != null) || (LeftLabels != null)) 
     {  
      g.Clear(BackColor); //tje error is in here. 
      g = CreateGraphics(); 
      /* another things to do*/ 
     } 
    } 
} 

Answer 1

你需要從OnPaint（）方法的圖形傳遞到您的DrawLabel（）方法。

變化：

DrawLabel(); 

要：

DrawLabel(e.Graphics); 

而變化：

private void DrawLabel() 

要：

private void DrawLabel(Graphics g) 

...並擺脫CreateGraphics（）調用。