C# 有趣的out参数

方法有多个返回值时我一般喜欢加out参数

private void button3_Click(object sender, EventArgs e)
        {
            int aa;
            AddI(out aa);
            textBox3.Text = aa.ToString();
        }

        private void AddI(out int vo)
        {
            int ss = Convert.ToInt32(textBox3.Text.Trim());
            vo = ss + 2;
        }
//textBox3+2

渐渐发现引用类型的参数不加out参数也是可以的，值类型就必须要加out

a、引用类型不加out

 private void button2_Click(object sender, EventArgs e)
        {
            List<string> list = new List<string>();
            AddList(list);

            StringBuilder stringBuilder = new StringBuilder();
            foreach (string ii in list)
            {
                stringBuilder.AppendLine(ii);
            }
            textBox2.Text += stringBuilder.ToString();
        }

        private void AddList(List<string> list)
        {
            list.Add("2");
            list.Add("3");
        }
//textBox2新增行2和3

b、值类型不加out

private void button1_Click(object sender, EventArgs e)
        {
            int ss = Convert.ToInt32(textBox1.Text.Trim());
            Add(ss);
            textBox1.Text = ss.ToString();
        }

        private int Add(int v)
        {
            return v += 2;
        }
//textBox1结果不变