场景: 对于输入框，如果用户不知道要输入什么，这个时候有个提示是最好了，下面是带提示说明的搜搜输入框，如图

C# Code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing;

namespace EMR
{
    public class SerachBox:TextBox
    {
        public string _HintString = "请输入住院号或姓名查询病历信息";
       
        public SerachBox()
        {
            this.Margin = new Padding(0,0,0,0);
            this._SerachButton.Text = "搜索";
            this._SerachButton.TextAlign = ContentAlignment.MiddleCenter;
            this._SerachButton.ForeColor = Color.Black;

            this._SerachButton.Margin = new Padding(0, 0, 0, 0);
            _SerachButton.BackColor = Color.Green;
            this.Text = _HintString;
            this.ForeColor = Color.Gray;
            _SerachButton.Size = new Size(60, this.Height);
            this.Controls.Add(_SerachButton);
            _SerachButton.Dock = DockStyle.Right;
            _SerachButton.Location = new Point(this.Width - 50, 0);
            _SerachButton.MouseHover += new EventHandler(ButtonHand);
            _SerachButton.MouseClick += new MouseEventHandler(ButtonClick);
        }

        private EventHandler serachHandler;
        public event EventHandler SerachEvent
        {
            add
            {
                serachHandler += value;
            }
            remove
            {
                serachHandler = value;
            }
        }

        public void ButtonClick(object sender, EventArgs e)
        {
            if(serachHandler !=null)
            {
                serachHandler.Invoke(this,null);
                this.Select(this.Text.Length,0);//光标移动到末尾
            }
        }
     

        public void ButtonHand(object sender, EventArgs e)
        {
           
            this._SerachButton.Cursor = System.Windows.Forms.Cursors.Hand;
        }

        public void SetFontColor(bool bo)
        {
            if (bo)
            {
                this.ForeColor = Color.Gray;
                this._SerachButton.ForeColor = Color.Black;
            }
            else
            {
                this.ForeColor = Color.Black;
                this._SerachButton.ForeColor = Color.Black;
            }
        }

        private Label _SerachButton = new Label();

        protected override void OnMouseDown(MouseEventArgs e)
        {
            base.OnMouseDown(e);
            //请输入住院号或姓名查询病历信息
            if (this.Text == _HintString)
            {
                this.Clear();
                this.SetFontColor(false);
            }
        }

        protected override void OnMouseLeave(EventArgs e)
        {
            base.OnMouseLeave(e);
            if (this.Focused && this.Text == "")
            {
                this.Text = _HintString;
                this.SetFontColor(true);
            }

           if (this.Text == _HintString)
            {
                this.SetFontColor(true);//显示灰色
            }
            else
            {
                this.SetFontColor(false);//显示黑色
            }
        }

        protected override void OnKeyPress(KeyPressEventArgs e)
        {
            base.OnKeyPress(e);
            e.Handled = true;
            if (this.Text ==  _HintString)
            {
                this.Text = "";
            }

            if(e.KeyChar.ToString() == "\r")
            {
                if (serachHandler != null)
                {
                    serachHandler.Invoke(this, null);
                    this.Select(this.Text.Length, 0);//光标移动到末尾
                }
            }

            this.SetFontColor(false);//显示黑色
            e.Handled = false;
        }

        protected override void OnMouseHover(EventArgs e)
        {
            base.OnMouseHover(e);

            if (this.Focused && this.Text == _HintString)
            {
                this.Text = "";
                this.SetFontColor(false);//显示黑色
            }

        }
    }
}

C# TextBox带提示说明的搜索输入框