【转】【C#】SendMessage

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();
}

private const int WM_SETTEXT = 0x000C;
private const int WM_GETTEXT = 0x000D;
private const int EM_GETRECT = 0x00b2;
private const int EM_SETRECT = 0x00b3;

原文地址：http://www.cnblogs.com/me-sa/articles/669402.html