C#初学问题。关于对话框点击取消出现错误信息

[geeklee]

我就用的帮助文件里面的那段代码，

private void button2_Click(object sender, System.EventArgs e)
{
Stream myStream ;
SaveFileDialog saveFileDialog1 = new SaveFileDialog();

saveFileDialog1.Filter = "All files (*.*)|*.*|txt files (*.txt)|*.txt" ;
saveFileDialog1.FilterIndex = 2 ;
saveFileDialog1.RestoreDirectory = true ;

if(saveFileDialog1.ShowDialog() == DialogResult.OK)
{
if((myStream = saveFileDialog1.OpenFile()) != null)
{
// Code to write the stream goes here.
myStream.Close();
}
}
richTextBox1.SaveFile(saveFileDialog1.FileName, RichTextBoxStreamType.PlainText);

}

我如果点击取消按钮就会出现错误对话框，说有不正常结尾，点击继续,程序继续执行，点击退出,程序关闭

[brbrm]

把最后一行
richTextBox1.SaveFile(saveFileDialog1.FileName, RichTextBoxStreamType.PlainText);
移到if语句里面

[brbrm]

是最里层的if((myStream = saveFileDialog1.OpenFile()) != null)
里面