MDI父

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WhyThread
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            Form2 f = new Form2(this);
            f.Show();
        }
    }
}


子窗口

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

namespace WhyThread
{
    public partial class Form2 : Form
    {
        Thread[] threads;

        public Form2(Form1 parent)
        {
            InitializeComponent();
            MdiParent = parent;
        }

        private void Form2_Load(object sender, EventArgs e)
        {

        }

        void Do()
        {
            richTextBox1.Text += DateTime.Now.ToString();
        }

        void ThreadProc(Object obj)
        {
            (obj as Form2).Do();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            threads = new Thread[100];
            for (int i = 0; i < threads.Length; i++)
            {
                threads[i] = new Thread(ThreadProc);
                threads[i].IsBackground = true;
                threads[i].Start(this);
            }
        }

    }
}