环境:XPsp2 + VS2005

说明:共两个窗体,每个窗体上有一个Button,点击Form1上的Button,则显示窗体Form2,同时Form1隐藏,点击Form2上的Button,则关闭Form2,同时Form1重现.Form2上的Button在鼠标进入和离开时会切换背景图片,背景图由一个imagelist保存.

代码:
//窗体Form1

public partial class Form1 : Form
{
private Form2 frm2;
public Form1()
{
InitializeComponent();
}

private void frm_Closed(object sender, FormClosedEventArgs e)
{
this.Show();
}

private void button1_Click(object sender, EventArgs e)
{
frm2 = new Form2 ();
frm2.FormClosed += new System.Windows.Forms.FormClosedEventHandler(frm_Closed);
frm2.Show();
this.Hide();
}
}

//窗体Form2
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}

private void Form2_FormClosed(object sender, FormClosedEventArgs e)
{

}

private void button1_Click(object sender, EventArgs e)
{
//MessageBox.Show("Before Button1_Click");
this.Close();
// MessageBox.Show("After Button1_Click");
}

private void button1_MouseEnter(object sender, EventArgs e)
{
this.button1.BackgroundImage = imageList1.Images[0];
}

private void button1_MouseLeave(object sender, EventArgs e)
{
//MessageBox.Show("Before Button1_MouseLeave");
//当点击Button1关闭窗体时,问题出在下面这句
//错误指向imagelist1,提示的信息是:InvalidArgument=“1”的值对于“index”无效。
//参数名: index.
//如果加上MessageBox语句,则不会出现错误.
this.button1.BackgroundImage = imageList1.Images[1]; //问题出在这里
//MessageBox.Show("After Button1_MouseLeave");
}
}

另外问下:Button1_Click事件是否一定将先触发Button1_MouseLeave事件.

button1.Visible = false; this.Close();的時候都會觸發Button1_MouseLeave;
問題可能是this.Close();執行的時候已經把控件imageList1 clear了;
在clear button1的時候觸發了Button1_MouseLeave;
執行this.button1.BackgroundImage = imageList1.Images[1];從而引發的錯誤。

我的想法与crazymk一样.不过还是没搞懂窗体销毁时,究竟是怎么处理资源回收的.在点击button1销毁窗体时,触发了mouse_Leave事件,此事件发生过程中,imagelist1对象还存在,但是images已经被销毁,即imagelist1是个没有内容的空对象了.不知道这么理解是否正确?

上列问题用以下方法已解决:
private void button1_MouseLeave(object sender, EventArgs e)
{
//检查imagelist是否为空对象
int count = imageList1.Images.Count;
//非空则调用图片
if (count !=0)
{
this.button1.BackgroundImage = this.imageList1.Images[1];
}
}
}