private void button1_Click(object sender, EventArgs e)        {            openFileDialog1.Filter = "*.txt|*.txt";//设置文件            DialogResult dr = openFileDialog1.ShowDialog();//显示打开文件对话框            if (dr ==DialogResult.OK)            {                richTextBox1.Text = System.IO.File.ReadAllText(openFileDialog1.FileName, Encoding.Default);            }        }
运行结果如图所示：