只需使用 Substring() 方法做一个小技巧:

Just do a trivial trick with Substring() method:

//KeyPress event handler for your richTextBox
private void richTextBox_KeyPress(object sender, KeyPressEventArgs e){
   if(e.KeyChar == ' '){
     int i = richTextBox.Text.TrimEnd().LastIndexOf(' ');
     if(i != -1) MessageBox.Show(richTextBox.Text.Substring(i+1).TrimEnd());
   }
}