去除文本多余空行

            OpenFileDialog dialog=new OpenFileDialog();
            dialog.InitialDirectory = Application.StartupPath;
            dialog.Filter = "All Files|*.*|text file(*.txt)|*.txt";
            dialog.RestoreDirectory = true;
            if (dialog.ShowDialog() == DialogResult.OK)
            {
                string filepath = dialog.FileName.ToString();
                string filename = filepath.Substring(filepath.LastIndexOf("\\") + 1);
                textBox1.Text = filepath;
                using (StreamReader sr = new StreamReader(filepath, Encoding.Default))//如果乱码，可改为System.Text.Encoding.UTF-8;或者System.Text.Encoding.GBK
                {
                    string str;
                    string line="";
                    while ((str = sr.ReadLine()) != null)
                    {
                        line+=str+"\n";
                    }
                    richTextBox1.Text = line;
                }
            }

        private void Form1_DragEnter(object sender, DragEventArgs e)
        {
            string path = ((System.Array)e.Data.GetData(DataFormats.FileDrop)).GetValue(0).ToString();
            textBox1.Text = path; //将获取到的完整路径赋值到textBox1
            using (StreamReader sr = new StreamReader(path, Encoding.Default))//如果乱码，可改为System.Text.Encoding.UTF-8;或者System.Text.Encoding.GBK
            {
                string str;
                string line = "";
                while ((str = sr.ReadLine()) != null)
                {
                    line += str + "\n";
                }
                richTextBox1.Text = line;
            }
        }

            richTextBox1.Clear();
            string[] xynet = File.ReadAllLines(textBox1.Text, Encoding.Default);
            for (int i = 0; i < xynet.Length; i++)
            {
                if (xynet[i].Trim() == "")
                {
                }
                else
                {
                    richTextBox1.Text+= xynet[i]+"\n";
                }
            }

            if (this.richTextBox1.Text == "")
                return;
            SaveFileDialog saveFileDialog1 = new SaveFileDialog();
            saveFileDialog1.DefaultExt = "txt";
            saveFileDialog1.Filter = "Text files (*.txt)|*.txt|All files (*.*)|*.*";
            if (saveFileDialog1.ShowDialog() == DialogResult.Cancel)
                return;
            string FileName = saveFileDialog1.FileName; 
            richTextBox1.SaveFile(saveFileDialog1.FileName, RichTextBoxStreamType.PlainText);

            textBox1.Text = string.Empty;
            richTextBox1.Text = string.Empty;