Form1中定义：
public static System.Windows.Forms.Button button1;

public partial class Form1 : Form
{
private int i = 0;
public Form1()
{
InitializeComponent();
button1.Text = "Start";
}

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

//========================================================

public partial class Form2 : Form
{
/// <summary>
/// Required designer variable.
/// </summary>
public Form2 ()
{
InitializeComponent();
FormClosed += new FormClosedEventHandler(Form2 _FormClosed);
}

void Form2 _FormClosed(object sender, FormClosedEventArgs e)
{
Form1.button1.Text = "End";
}
}

FormClosed += new FormClosedEventHandler(Form2 _FormClosed);
(Form2 _FormClosed);//这里报错，无效表达式

你要写这个事件的方法呀

void Form2 _FormClosed(object sender, FormClosedEventArgs e)
{
Form1.button1.Text = "End";
}

写了的

郁闷```
我测试过的

我也不知道哦
其实我觉得你这种方法挺好的
不用定义静态变量

查出来了
多了一个空格
编译通过

呵呵