C# winfrom提示框，点击则不显示，不点击则提示输入内容

先看下效果图，初次进来是界面左边的效果，点击请输入账号，清除内容，可以直接输入，右边图

                          

以下代码是失去焦点的，一定要把控件的属性TabStop 改为false。不然是不行的。

   #region 失去焦点
        protected override bool ProcessTabKey(bool forward)
        {
            foreach (Control c in this.Controls)
            {
                if (c is TextBox)
                {
                    c.TabStop = true;
                }
            }
            return base.ProcessTabKey(forward);
        }
        #endregion

水印类

把水印类添加在项目中。直接调用方法即可ComLogin_Load

 /// <summary>
  /// 基于.NET 2.0的TextBox工具类
  /// </summary>
  public static class TextBoxToolV2
  {
    private const int EM_SETCUEBANNER = 0x1501;
    [DllImport("user32.dll", CharSet = CharSet.Auto)]

    private static extern Int32 SendMessage
     (IntPtr hWnd, int msg, int wParam, [MarshalAs(UnmanagedType.LPWStr)] string lParam);

    /// <summary>
    /// 为TextBox设置水印文字
    /// </summary>
    /// <param name="textBox">TextBox</param>
    /// <param name="watermark">水印文字</param>
    public static void SetWatermark(this TextBox textBox, string watermark)
    {
      SendMessage(textBox.Handle, EM_SETCUEBANNER, 0, watermark);
    }
    /// <summary>
    /// 清除水印文字
    /// </summary>
    /// <param name="textBox">TextBox</param>
    public static void ClearWatermark(this TextBox textBox)
    {
      SendMessage(textBox.Handle, EM_SETCUEBANNER, 0, string.Empty);
    }
  }

  private void ComLogin_Load(object sender, EventArgs e)
       {
           this.WindowState = FormWindowState.Maximized;
           TextBoxToolV2.SetWatermark(txtUserID, "请输入账号");
           TextBoxToolV2.SetWatermark(txtEntryPwd, "请输入密码");

        }