闲的蛋疼，写的打字游戏

目前还有2个问题：1、快速的时候苹果会闪；2、重叠问题

下面代码：

字母信息类

using System;
using System.Collections.Generic;
using System.Text;

namespace CharDown
{
    class CharClass
    {
        public CharClass(int _x, int _y, char _char, bool _isChecked, int _moveSize)
        {
            X = _x;
            Y = _y;
            Char_key = _char;
            IsChecked = _isChecked;
            MoveSize = _moveSize;
        }
        private int x;

        /// <summary>
        /// X
        /// </summary>
        public int X
        {
            get { return x; }
            set { x = value; }
        }
        private int y=0;

        /// <summary>
        /// Y
        /// </summary>
        public int Y
        {
            get { return y; }
            set { y = value; }
        }
        private char char_key;

        /// <summary>
        /// 当前字母
        /// </summary>
        public char Char_key
        {
            get { return char_key; }
            set { char_key = value; }
        }
        private bool isChecked=false;

        /// <summary>
        /// 是否击中
        /// </summary>
        public bool IsChecked
        {
            get { return isChecked; }
            set { isChecked = value; }
        }
        private int moveSize=10;

        /// <summary>
        /// 移动距离
        /// </summary>
        public int MoveSize
        {
            get { return moveSize; }
            set { moveSize = value; }
        }
    }
}

主窗体

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

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

        List<CharClass> charClassList = new List<CharClass>();
        List<char> charlist = new List<char>();
        static object _obj = new object();
        int panelWidth = 0;
        int panelHeigh = 0;
        bool isStop = false;
        int sleepMin = 0;
        int sleepMax = 0;
        bool islianxi = true;
        private char GetChar()
        {
            lock (_obj)
            {
                char c;
                string strs = "ABCDEFGHIGKLMNOPQRSTUVWXYZ";
                char[] chars = strs.ToCharArray();
                Random r = new Random();
                int _index = r.Next(0, chars.Length);
                c = chars[_index];
                return c;
            }
        }

        private void 开始ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            switch (this.toolStripComboBox1.SelectedIndex)
            {
                case 0: sleepMin = 100; sleepMax = 200; break;
                case 1: sleepMin = 50; sleepMax = 100; break;
                case 2: sleepMin = 10; sleepMax = 50; break;
            }
            if (this.toolStripComboBox2.SelectedIndex == 0)
            {
                islianxi = true;
            }
            else
            {
                islianxi = false;
            }
            panelWidth = this.panel1.Width - 30;
            panelHeigh = this.panel1.Height - 20;
            this.toolStripLabel2.Text = "0";
            this.toolStripLabel2.ForeColor = Color.Black;
            this.Focus();
            //this.panel1.Focus();
            isStop = false;
            Thread server = new Thread(new ThreadStart(Server));
            server.IsBackground = true;
            server.Start();
            // Server();
        }

        private void Server()
        {
            while (true && !isStop)
            {
                Thread _th = new Thread(new ThreadStart(Begin));
                _th.IsBackground = true;
                _th.Start();
                Thread.Sleep(500);
            }

        }

        private void Begin()
        {
            char _char;
            while (true)
            {
                _char = GetChar();
                if (!charlist.Contains(_char))
                {
                    break;
                }
            }
            charlist.Add(_char);
            Random r = new Random();
            int x = r.Next(0, panelWidth);
            int sleeptime = r.Next(sleepMin, sleepMax);
            CharClass _class = new CharClass(x, 0, _char, false, 5);
            charClassList.Add(_class);
            Color c = this.panel1.BackColor;
            Font font = new System.Drawing.Font("宋体", 20, FontStyle.Bold);
            Graphics g = this.panel1.CreateGraphics();
            while (true && !isStop)
            {
                Bitmap image = new Bitmap(Application.StartupPath + "\\app.png");
                
                if (_class.IsChecked)
                {
                    ClearImage(_class, g, c, image);
                   // ClearString(_class, g, c);
                    charlist.Remove(_class.Char_key);
                    charClassList.Remove(_class);
                    if (!islianxi)
                    {
                        this.toolStripLabel2.Text = (Convert.ToInt32(this.toolStripLabel2.Text) + 1).ToString();
                        if (Convert.ToInt32(this.toolStripLabel2.Text) == 100)
                        {
                            isStop = true;
                            MessageBox.Show("恭喜您通过了");
                        }
                    }
                    break;
                }
                DrawImage(_class, g, c, font, image);
                //DrawString(_class, g, c, font);
                if (_class.Y >= panelHeigh)
                {
                    ClearImage(_class, g, c, image);
                    //ClearString(_class, g, c);
                    charlist.Remove(_class.Char_key);
                    charClassList.Remove(_class);
                    if (!islianxi)
                    {
                        this.toolStripLabel2.Text = (Convert.ToInt32(this.toolStripLabel2.Text) - 1).ToString();
                        if (Convert.ToInt32(this.toolStripLabel2.Text) < 0)
                        {
                            isStop = true;
                            MessageBox.Show("游戏结束");
                        }
                    }
                    return;
                }
                Thread.Sleep(sleeptime);
            }
            g.Clear(c);
          
           // ClearString(_class, g, c);
        }
        private void DrawString(CharClass _class, Graphics g, Color c, Font font)
        {
            if (_class.Y != 0)
            {
                ClearString(_class, g, c);
            }
            _class.Y = _class.Y + _class.MoveSize;
            g.DrawString(_class.Char_key.ToString(), font, new SolidBrush(Color.Black), _class.X, _class.Y);
        }

        private void DrawImage(CharClass _class, Graphics gp, Color c, Font font, Bitmap image)
        {
            Graphics g = Graphics.FromImage(image);
            g.DrawString(_class.Char_key.ToString(), font, new SolidBrush(Color.Black), image.Width / 2 - 13, image.Height / 2 - 10);

            if (_class.Y != 0)
            {
                ClearImage(_class, gp, c, image);
            }
            _class.Y = _class.Y + _class.MoveSize;
            gp.DrawImage(image, _class.X, _class.Y);
        }

        private void ClearImage(CharClass _class, Graphics g, Color c, Bitmap image)
        {
            g.FillRectangle(new SolidBrush(c), _class.X, _class.Y, image.Width, image.Height);
        }

        private void ClearString(CharClass _class, Graphics g, Color c)
        {
            g.FillRectangle(new SolidBrush(c), _class.X, _class.Y, 30, 30);
        }

        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            Application.Exit();
        }

        private void toolStripButton2_Click(object sender, EventArgs e)
        {
            isStop = true;
            Graphics g = this.panel1.CreateGraphics();
            g.Clear(this.panel1.BackColor);
        }

        private void Form1_KeyDown(object sender, KeyEventArgs e)
        {
            int key = e.KeyValue;
            if (key >= 65 && key <= 90)
            {
                if (charlist.Contains(Convert.ToChar(e.KeyCode)))
                {
                    foreach (CharClass c in charClassList)
                    {
                        if (c.Char_key.ToString().ToUpper() == e.KeyCode.ToString().ToUpper())
                        {
                            c.IsChecked = true;
                            if (!islianxi)
                            {
                                this.toolStripLabel2.Text = (Convert.ToInt32(this.toolStripLabel2.Text) + 1).ToString();
                                if (Convert.ToInt32(this.toolStripLabel2.Text) == 100)
                                {
                                    isStop = true;
                                    MessageBox.Show("恭喜您通过了");
                                }
                            }
                            return;
                        }
                    }
                }
                else if (!islianxi)
                {
                    this.toolStripLabel2.Text = (Convert.ToInt32(this.toolStripLabel2.Text) - 1).ToString();
                    if (Convert.ToInt32(this.toolStripLabel2.Text) < 10)
                    {
                        this.toolStripLabel2.ForeColor = Color.Red;
                    }

                    if (Convert.ToInt32(this.toolStripLabel2.Text) < 0)
                    {
                        isStop = true;
                        MessageBox.Show("游戏结束");
                    }
                }
            }
        }

        private void toolStripButton3_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            this.toolStripComboBox1.SelectedIndex = 0;
            this.toolStripComboBox2.SelectedIndex = 0;
        }
    }
}

望批评指正，可执行文件地址http://pan.baidu.com/share/link?shareid=204227&uk=33979446