C# 跨窗体事件

using System;
using System.Drawing;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        private Form2 _frm;
        public Form1()
        {
            InitializeComponent();
            
        }

        private void button1_Click(object sender, EventArgs e)
        {
            var form2 = new Form2();
            _frm = form2;
            form2.Show();
        }

        public bool IsClick;
        private void button2_Click(object sender, EventArgs e)
        {
            IsClick = !IsClick;
            if (IsClick)
                _frm.button1.BackColor = Color.Red;
            else if (IsClick == false)
            {
                _frm.button1.BackColor = SystemColors.Control;
            }
        }
    }
}