C#中使用SendMessage

原文：http://www.csharpwin.com/csharpspace/11376r7140.shtml

备注：主要描述在调用API函数SendMessage时数据类型的转换。

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SendMessage是一个在user32.dll中声明的API函数，在C#中导入如下：

using System.Runtime.InteropServices;

[DllImport("user32.dll", EntryPoint="SendMessageA")]

public static extern int SendMessage (IntPtr hwnd, int wMsg, IntPtr wParam, IntPtr lParam);

本文描述其参数 lParam 的用法，主要是数据类型之间的转化。

● 一种最简单的处理方式是声明多个SendMessage函数(overload)，用所需的数据类型直接替换IntPtr。例如：

//声明:

[DllImport("user32.dll", EntryPoint="SendMessageA")]

private static extern int SendMessage (IntPtr hwnd, 

   int wMsg, IntPtr wParam, string lParam);

[DllImport("user32.dll", EntryPoint="SendMessageA")]

private static extern int SendMessage (IntPtr hwnd, int wMsg, 

    IntPtr wParam, ref Rectangle lParam);

//调用:

string s = "hello, floodzhu";

SendMessage(this.textBox1.Handle, WM_SETTEXT, IntPtr.Zero, s);



Rectangle rect = new Rectangle();

SendMessage(this.richTextBox1.Handle, EM_GETRECT, (IntPtr)0, ref rect);


● 对要求返回字符串的类型（out string）可以用 StringBuilder 代替，此时不需要 out/ref。例如：

[DllImport("user32.dll", EntryPoint="SendMessageA")]

private static extern int SendMessage (IntPtr hwnd, int wMsg,

     int wParam, StringBuilder lParam);

private void button1_Click(object sender, System.EventArgs e)

{

     const int buffer_size = 1024;

     StringBuilder buffer = new StringBuilder(buffer_size);

     SendMessage(this.textBox1.Handle, WM_GETTEXT, buffer_size, buffer);

     //MessageBox.Show(buffer.ToString());

}


● 如果想用 InPtr 类型统一处理的话，可以借助于 Marshal 或者 GCHandle 的相关方法。例如：

[DllImport("user32.dll", EntryPoint="SendMessageA")]

private static extern int SendMessage (IntPtr hwnd, int wMsg, 
   IntPtr wParam, IntPtr lParam);



private void button2_Click(object sender, System.EventArgs e)

{

      Rectangle rect = new Rectangle();

      IntPtr buffer = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(Rectangle)));

      Marshal.StructureToPtr(rect, buffer ,true);



      SendMessage(this.richTextBox1.Handle, EM_GETRECT, (IntPtr)0, buffer);



      rect = (Rectangle)Marshal.PtrToStructure(buffer, typeof(Rectangle));



      Marshal.FreeHGlobal(buffer);

}

或者

private void button2_Click(object sender, System.EventArgs e)

{

      Rectangle rect = new Rectangle();

      GCHandle gch = GCHandle.Alloc(rect);



      SendMessage(this.richTextBox1.Handle, EM_GETRECT, (IntPtr)0, (IntPtr)gch);

      rect = (Rectangle)Marshal.PtrToStructure((IntPtr)gch, typeof(Rectangle));



      gch.Free();

}

作者：azlao