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 _04TextBox{    public partial class Form1 : Form    {        List
     
       Data = new List
      
       ();        string Randomstr = "功夫撒黑胡椒hcbvf蜂窝qwertyuiopasdfghjklzxcvbnm法国的恢复到飞范德萨QWERTYUIOPASDFGHJKLZXCVBNM出现过热423贴①46546也有一头热刚恢复到贴3天赋如头3广泛的我让他";        Random rd = new Random(GetRandomSeed());        static int GetRandomSeed()        {            byte[] bytes = new byte[4];            System.Security.Cryptography.RNGCryptoServiceProvider rng = new System.Security.Cryptography.RNGCryptoServiceProvider();            rng.GetBytes(bytes);            return BitConverter.ToInt32(bytes, 0);        }        public Form1()        {            InitializeComponent();            //2000W数据，这里会有卡顿现象，这里修改为200W            for (int i = 0; i < 2000000; i++)            {                Data.Add(Randomstr.ToCharArray()[rd.Next(Randomstr.Length)].ToString()                    + Randomstr.ToCharArray()[rd.Next(Randomstr.Length)].ToString()                    + Randomstr.ToCharArray()[rd.Next(Randomstr.Length)].ToString()                    + Randomstr.ToCharArray()[rd.Next(Randomstr.Length)].ToString()                    + Randomstr.ToCharArray()[rd.Next(Randomstr.Length)].ToString());            }            //重点代码            this.textBox1.AutoCompleteCustomSource.Clear();            this.textBox1.AutoCompleteCustomSource.AddRange(Data.ToArray());            this.textBox1.AutoCompleteMode = System.Windows.Forms.AutoCompleteMode.SuggestAppend;            this.textBox1.AutoCompleteSource = System.Windows.Forms.AutoCompleteSource.CustomSource;        }        private void Form1_Load(object sender, EventArgs e)        {        }    }}
      
     

 提示内容，加个变量跟两个事件

#region 实现提示文字        Boolean textboxHasText = false;//判断输入框是否有文本         /// 
        /// textbox获得焦点        /// 
        ///         ///         private void textBox1_Enter(object sender, EventArgs e)        {            if (textboxHasText == false)                textBox1.Text = "";            textBox1.ForeColor = Color.Black;        }        /// 
        /// textbox失去焦点          /// 
        ///         ///         private void textBox1_Leave(object sender, EventArgs e)        {            if (textBox1.Text == "")            {                textBox1.Text = "提示内容";                textBox1.ForeColor = Color.LightGray;                textboxHasText = false;            }            else                textboxHasText = true;        }        #endregion