子窗体控制父窗体的内容

//父窗体
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 WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        public void add(string str)
        {
            textBox1.Text = str;
        }
        private void button1_Click(object sender, EventArgs e)
        {
            Form2 f = new Form2();
            //事件 赋予方法
            f.mydev += add;
            f.Show();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}

//子窗体
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 WindowsFormsApplication1
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }
        public delegate void mydel(string str);
        public event mydel mydev;
        private void button1_Click(object sender, EventArgs e)
        {
//触发事件
            mydev(textBox1.Text);
        }
    }
}