C# 对其他窗口发送文本

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace mysend
{

    public partial class Form1 : Form
    {
        const int WM_SETTEXT = 0x0C;
        IntPtr targethwnd;

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {

            IntPtr buffer = Marshal.AllocHGlobal(Marshal.SizeOf(textBox2.Text.Length+1));
            Marshal.Copy(textBox2.Text.ToCharArray(), 0, buffer, textBox2.Text.Length);
            targethwnd = (IntPtr)Int32.Parse(textBox1.Text);
            SendMessage(targethwnd , WM_SETTEXT, IntPtr.Zero, buffer);
            Marshal.FreeHGlobal(buffer);
        }
    }
}

发送文本时SendMessage第四个字段是InPtr类型，要使用Marshal；

发送之后释放buffer，否则多几次就出问题；

目标句柄手动填入，发送到记事本；

更改计算器窗口的标题也是可以的；