如何让文本框显示提示信息

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QQ上输入账号密码的时候会有一个提示信息，这个是如何实现的呢？

正文

        //用户名自动提示
        private void txtUserID_Enter(object sender, EventArgs e)
        {
            txtUserID.Focus();
            txtUserID.Text = "请输入用户名";

            txtUserID.ForeColor = Color.LightGray;
        }

        private void txtUserID_Leave(object sender, EventArgs e)
        {
            if (txtUserID.Text == "")
            {
                txtUserID.Text = "请输入用户名";
                txtUserID.ForeColor = Color.LightGray;
            }

        }
        //点击用户文本框，内容清空
        private void txtUserID_MouseClick(object sender, MouseEventArgs e)
        {
            txtUserID.Text = "";
        }

        private void txtPassWord_MouseClick(object sender, MouseEventArgs e)
        {
            txtPassWord.Text = "";
        }



        //密码自动提示
        private void txtPassWord_Enter(object sender, EventArgs e)
        {
            txtPassWord.Text = "请输入密码";
            txtPassWord.ForeColor = Color.LightGray;
        }
        //离开自动回复密码提示
        private void txtPassWord_Leave(object sender, EventArgs e)
        {
            if (txtPassWord.Text == "")
            {
                txtPassWord.Text = "请输入密码";
                txtPassWord.ForeColor = Color.LightGray;
            }

        }
        //密码框为*
        private void txtPassWord_TextChanged(object sender, EventArgs e)
        {
            if (txtPassWord.Text == "" && txtPassWord.Text != "请输入密码")
            {
                txtPassWord.PasswordChar = Convert.ToChar("*");
            }

        }
        

小结

这个功能逻辑有点绕，还需要再研究一下。