private void btnopen_Click(object sender, EventArgs e)
        {
            string fname;
            openFileDialog1.ShowDialog();
            fname=openFileDialog1.FileName;
            if (openFileDialog1.ShowDialog() == DialogResult.Cancel)
            { return; }
            if (fname != "")
            {
                if (openFileDialog1.FilterIndex == 1)
                    richTextBox1.LoadFile(fname, RichTextBoxStreamType.PlainText);
                else
                    richTextBox1.LoadFile(fname,RichTextBoxStreamType.RichText);
            }
        }
还有：对话框还有其它异常吗？
打开对话框不一定就要点击打开，应该还有其它操作，如取消，如点击右上角的X按钮 ，这些操作该如何捕捉？
多谢帮忙

不论是打开，还是取消，都出现两次，真晕~~

那是因为你叫它打开了两次，所以它才听话的。
改成下面这样看看。

private void btnopen_Click(object sender, EventArgs e)
        {
            string fname;
            //openFileDialog1.ShowDialog();
            if (openFileDialog1.ShowDialog() == DialogResult.Cancel)
            { return; }
             fname=openFileDialog1.FileName;       //new place here.
            if (fname != "")
            {
                if (openFileDialog1.FilterIndex == 1)
                    richTextBox1.LoadFile(fname, RichTextBoxStreamType.PlainText);
                else
                    richTextBox1.LoadFile(fname,RichTextBoxStreamType.RichText);
            }
        }

jack正解，

            openFileDialog1.ShowDialog();                          //打开一次
            if (openFileDialog1.ShowDialog() == DialogResult.Cancel)    //打开一次

正确 ~~~问题解决~

ＹＥＳ．．．．

暄暄....
干嘛叫YES...啊???

正解

你们在说暗语
我貌似懂一点哦