用到的东西有 API引用 句柄 等，都是前面需要的。会在进程间发送消息，做个按键外挂是没问题的！（向游戏发送按键信息）

首先建立两个C#应用程序项目。

第一个项目包含一个Windows Form(Form1),在Form1上有一个Button和一个TextBox。

第二个项目包含一个Windows Form(Form1),在Form1上有两个Button，分别用来测试第一个应用程序中Button的Click事件和修改第一个应用程序中TextBox的值。

第一个应用程序中Form的代码如下:

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;

public class Form1 : System.Windows.Forms.Form {
private System.Windows.Forms.Button button1;
private System.Windows.Forms.TextBox textBox1;

private System.ComponentModel.Container components = null;

[STAThread]
static void Main() {
Application.Run(new Form1());
}

public Form1()
{
InitializeComponent();
}
protected override void Dispose( bool disposing )
{
if( disposing )
{
if(components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows 窗体设计器生成的代码
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.textBox1 = new System.Windows.Forms.TextBox();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(32, 24);
this.button1.Name = "button1";
this.button1.TabIndex = 0;
this.button1.Text = "button1";
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// textBox1
//
this.textBox1.Location = new System.Drawing.Point(32, 64);
this.textBox1.Name = "textBox1";
this.textBox1.TabIndex = 1;
this.textBox1.Text = "textBox1";
//
// Form1
//
this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
this.ClientSize = new System.Drawing.Size(292, 266);
this.Controls.Add(this.textBox1);
this.Controls.Add(this.button1);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);

}
#endregion

private void button1_Click(object sender, System.EventArgs e) {
MessageBox.Show("This is button1 click!");
}
}

第二个应用程序中Form的代码如下:

using System;
using System.Text;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Runtime.InteropServices;

public class TestForm1 : System.Windows.Forms.Form {
private System.Windows.Forms.Button button1;
private System.Windows.Forms.Button button2;

private System.ComponentModel.Container components = null;

[STAThread]
static void Main() {
Application.Run(new TestForm1());
}

public TestForm1()
{
InitializeComponent();
}
protected override void Dispose( bool disposing )
{
if( disposing )
{
if(components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows 窗体设计器生成的代码
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.button2 = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(32, 24);
this.button1.Name = "button1";
this.button1.TabIndex = 0;
this.button1.Text = "button1";
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// button2
//
this.button2.Location = new System.Drawing.Point(32, 64);
this.button2.Name = "button2";
this.button2.TabIndex = 0;
this.button2.Text = "button2";
this.button2.Click += new System.EventHandler(this.button2_Click);
//
// TestForm1
//
this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
this.ClientSize = new System.Drawing.Size(292, 266);
this.Controls.Add(this.button1);
this.Controls.Add(this.button2);
this.Name = "TestForm1";
this.Text = "TestForm1";
this.ResumeLayout(false);

}
#endregion

private void button1_Click(object sender, System.EventArgs e) {
IntPtr hwnd_win ;
IntPtr hwnd_button ;

hwnd_win = FindWindow("WindowsForms10.Window.8.app3","Form1");
hwnd_button = FindWindowEx(hwnd_win ,new IntPtr(0) ,"WindowsForms10.BUTTON.app3","button1");

const int BM_CLICK = 0x00F5;
Message msg = Message.Create(hwnd_button ,BM_CLICK ,new IntPtr(0),new IntPtr(0));
PostMessage(msg.HWnd ,msg.Msg ,msg.WParam ,msg.LParam);
}
private void button2_Click(object sender, System.EventArgs e) {
const int WM_CHAR = 0x0102;
IntPtr hwnd_win ;
IntPtr hwnd_textbox ;

hwnd_win = FindWindow("WindowsForms10.Window.8.app3","Form1");
hwnd_textbox = FindWindowEx(hwnd_win ,new IntPtr(0) ,"WindowsForms10.EDIT.app3","textBox1");

string strtext = "测试aaa";
UnicodeEncoding encode = new UnicodeEncoding();
char[] chars = encode.GetChars(encode.GetBytes(strtext));
Message msg ;
foreach (char c in chars ) {
msg = Message.Create(hwnd_textbox ,WM_CHAR ,new IntPtr(c),new IntPtr(0));
PostMessage(msg.HWnd ,msg.Msg ,msg.WParam ,msg.LParam);
}
}

[DllImport("user32.dll")]
public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

[DllImport("user32.dll")]
public static extern IntPtr FindWindowEx(IntPtr hwndParent,IntPtr hwndChildAfter,string lpszClass,string lpszWindow);

[DllImport("user32.dll",CharSet=CharSet.Unicode)]
public static extern IntPtr PostMessage(IntPtr hwnd,int wMsg,IntPtr wParam,IntPtr lParam);
}

以上代码可以在VS.NET中编译运行，也可以使用csc.exe编译,如使用一下命令行：

F:>csc.exe Form1.cs

F:>csc.exe TestForm1.cs

编译后生成两个.exe文件。

首先运行第一个程序，显示Form1窗体，然后运行第二个程序，显示TestForm1窗体。

在TestForm1窗体上点击button1按钮（向Form1窗体上的button1发送消息）此时显示对话框提示“This is button1 click!”。

在TestForm1窗体上点击button2按钮（向Form1窗体上的textBox1发送消息）此时在Form1上的textBox1上显示“测试aaa”。