using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private Label lbl = null;
        private void Form1_Load(object sender, EventArgs e)
        {
            lbl = new Label();
            lbl.Text = "入力してください。";
            lbl.Cursor = Cursors.IBeam;
            lbl.Click += lbl_Click;
            lbl.Anchor = AnchorStyles.Right;
            lbl.AutoSize = true;
            lbl.BackColor = Color.Transparent;
            lbl.ForeColor = Color.Gray;
            textBox1.Enter += lbl_Click;
            textBox1.Leave += textBox1_Leave;
            textBox1.Controls.Add(lbl);
        }

        void textBox1_Leave(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(textBox1.Text))
            {
                lbl.Visible = true;
            }
        }


        void lbl_Click(object sender, EventArgs e)
        {
            this.lbl.Visible = false;
            this.textBox1.Focus();
        }
    }
}