Windows程序更改子窗口控件的父窗口

可以用Win32 函数SetParent()更改窗口的父窗口；下面先做个简单程序看一下是什么效果；

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 setpdemo
{
    public partial class Form1 : Form
    {
        Form2 frm2;

        [DllImport("user32.dll", CharSet = CharSet.Unicode)]
        static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            frm2 = new Form2();
            frm2.Show();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            SetParent(button3.Handle, frm2.Handle);
        }

        private void button3_Click(object sen