1.创建一个C# windows应用程序

　　2.添加一个windows表单Label到Form1.cs

　　3.单击label1控件然后更改Text属性为空字符

　　4.更改BorderStyle属性为FixedSingle

　　5.右键单击Form1.cs，然后点击View Code

　　添加下面Using语句到Form1.cs源码的顶部

　　6.using System.Runtime.InteropServices;

　　注意该步骤添加必要的引用来调用InteropServices函数和方法

　　7.private Bitmap myBitmap;

　　添加下面的Win32APICall 类到Form1.cs中的Form1类后面

public class Win32APICall
{
[DllImport("gdi32.dll",EntryPoint="DeleteDC")]
public static extern IntPtr DeleteDC(IntPtr hdc);
[DllImport("gdi32.dll",EntryPoint="DeleteObject")]
public static extern IntPtr DeleteObject(IntPtr hObject);
[DllImport("gdi32.dll",EntryPoint="BitBlt")]
public static extern bool BitBlt(IntPtr hdcDest,int nXDest,
int nYDest,int nWidth,int nHeight,IntPtr hdcSrc,
int nXSrc,int nYSrc,int dwRop);
[DllImport ("gdi32.dll",EntryPoint="CreateCompatibleBitmap")]
public static extern IntPtr CreateCompatibleBitmap(IntPtr hdc,
int nWidth, int nHeight);
[DllImport ("gdi32.dll",EntryPoint="CreateCompatibleDC")]
public static extern IntPtr CreateCompatibleDC(IntPtr hdc);
[DllImport ("gdi32.dll",EntryPoint="SelectObject")]
public static extern IntPtr SelectObject(IntPtr hdc,IntPtr hgdiobjBmp);
[DllImport("user32.dll", EntryPoint="GetDesktopWindow")]
public static extern IntPtr GetDesktopWindow();
[DllImport("user32.dll",EntryPoint="GetDC")]
public static extern IntPtr GetDC(IntPtr hWnd);
[DllImport("user32.dll",EntryPoint="GetSystemMetrics")]
public static extern int GetSystemMetrics(int nIndex);
[DllImport("user32.dll",EntryPoint="ReleaseDC")]
public static extern IntPtr ReleaseDC(IntPtr hWnd,IntPtr hDC);
public static Bitmap GetDesktop()
{
　 int screenX;
　 int screenY;
　 IntPtr hBmp;
　 IntPtr hdcScreen = GetDC(GetDesktopWindow());
　 IntPtr hdcCompatible = CreateCompatibleDC(hdcScreen);
　 screenX = GetSystemMetrics(0);
　 screenY = GetSystemMetrics(1);
　 hBmp = CreateCompatibleBitmap(hdcScreen, screenX, screenY);
　 if (hBmp!=IntPtr.Zero)
　 {
　　　IntPtr hOldBmp = (IntPtr) SelectObject(hdcCompatible, hBmp);
　　　BitBlt(hdcCompatible, 0, 0,screenX,screenY, hdcScreen, 0, 0,13369376);
　　　SelectObject(hdcCompatible, hOldBmp);
　　　DeleteDC(hdcCompatible);
　　　ReleaseDC(GetDesktopWindow(), hdcScreen);
　　　Bitmap bmp = System.Drawing.Image.FromHbitmap(hBmp);
　　　DeleteObject(hBmp);
　　　GC.Collect();
　　　return bmp;
　 }
　 return null;
　 }
}该步骤添加用于调用非托管windows GDI API函数所需的变量，结构和DllImport语句

　　8.添加下面代码到在第二步创建的标签的MouseDown 事件中

　　private void label1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e){　　myBitmap = Win32APICall.GetDesktop();}

　　9.添加下面代码到第二步创建的标签的MouseUp 事件中

　　private void label1_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e){　　Color myColor = myBitmap.GetPixel(MousePosition.X,MousePosition.Y);　　label1.BackColor = myColor;}

　　10.点击运行，单击并保持鼠标按钮在标签上保持按下状态，在桌面拖动鼠标指针，然后释放鼠标按钮来捕获颜色