练手WPF(四)——贪吃蛇小游戏的简易实现（下）

八、生成新的单节蛇身
我们这里先说说游戏小原理好了，游戏运行后，通过计时器事件不断生成新的单节蛇身类SnakeNode，添加到List中的0位置，原来的蛇头变成了第二节。该节新蛇头的坐标通过蛇头前进方向Direct进行判断，即如果原蛇头往左运行，则新蛇头在原蛇头位置的左一格生成，其他方向以此类推。最后将该节添加到SnakeNodes列表中，并将相应图形添加到游戏区。

private void GenNewSnakeNode()
{
    SnakeNode snakeNode = null;
    switch (Direct)
    {
        case Direction.UP:
            snakeNode = new SnakeNode(new Point(SnakeNodes[SnakeHead]._pos.X,
                SnakeNodes[SnakeHead]._pos.Y - 1));
            break;

        case Direction.DOWN:
            snakeNode = new SnakeNode(new Point(SnakeNodes[SnakeHead]._pos.X,
                SnakeNodes[SnakeHead]._pos.Y + 1));
            break;

        case Direction.LEFT:
            snakeNode = new SnakeNode(new Point(SnakeNodes[SnakeHead]._pos.X - 1,
                SnakeNodes[SnakeHead]._pos.Y));
            break;

        case Direction.RIGHT:
            snakeNode = new SnakeNode(new Point(SnakeNodes[SnakeHead]._pos.X + 1,
                SnakeNodes[SnakeHead]._pos.Y));
            break;
    }

    if (snakeNode != null)
    {
        SnakeNodes.Insert(0, snakeNode);
        myCanvas.Children.Add(SnakeNodes[0]._rect);
    }
}

九、随机水果位置
注意该新位置不得与蛇身任何一节重叠，如果重叠则另外生成新位置，直到成功为止。

private Point SetFruitToRandomPos()
{
    bool flag = true;
    Point pos = new Point();
    while (flag)
    {
        flag = false;
        pos = new Point(rnd.Next(0, CellWidth), rnd.Next(0, CellHeight));
        foreach (var node in SnakeNodes)
        {
            if (pos.X == node._pos.X && pos.Y == node._pos.Y)
            {
                flag = true;
                break;
            }
        }
    }

    return pos;
}

十、碰撞检测（蛇头与水果）
因为只有蛇头会最先触碰到水果，所以只需判断蛇头坐标与水果坐标是否相同即可。如果撞到水果，则将水果随机生成新位置；如果没有碰到，则删除蛇尾一节（因为之后会通过计时器会生成新一节蛇头，这样就会保存蛇身长度，感觉位置前进了一格）。

private void CheckCollision()
{
    if (SnakeNodes[SnakeHead]._pos.X == fruit._pos.X && SnakeNodes[SnakeHead]._pos.Y == fruit._pos.Y)
    {
        fruit.SetPostion(SetFruitToRandomPos());
    }
    else
    {
        if (myCanvas.Children.Contains(SnakeNodes[SnakeNodes.Count - 1]._rect))
            myCanvas.Children.Remove(SnakeNodes[SnakeNodes.Count - 1]._rect);

        SnakeNodes.RemoveAt(SnakeNodes.Count - 1);
    }
}

十一、判断是否游戏结束
很简单，看看蛇头是否触碰游戏区四边或蛇身的任何一节，如果是则返回true。
注意蛇身循环是从1开始的，如果从0开始你知道会出现什么情况。

        private bool IsGameOver()
        {
            if (SnakeNodes[SnakeHead]._pos.X == -1 || SnakeNodes[SnakeHead]._pos.X == CellWidth
                || SnakeNodes[SnakeHead]._pos.Y == -1 || SnakeNodes[SnakeHead]._pos.Y == CellHeight)
            {
                return true;
            }

            foreach (var node in SnakeNodes)
            {
                if (node == SnakeNodes[SnakeHead])
                    continue;

                if (node._pos.X == SnakeNodes[SnakeHead]._pos.X && node._pos.Y == SnakeNodes[SnakeHead]._pos.Y)
                {
                    return true;
                }
            }

            return false;
        }

十三、删除游戏区的所有蛇身节
这个会在重新开始游戏时使用到：

private void RemoveSnakeNodeAll()
{
    for (int i = 0; i < SnakeNodes.Count; i++)
    {
        if (myCanvas.Children.Contains(SnakeNodes[i]._rect))
        {
            myCanvas.Children.Remove(SnakeNodes[i]._rect);
        }
    }
}

顺便再来一发删除游戏区的水果：

private void RemoveFruit()
{
    if (fruit == null) 
    {
        return;
    }

    if (myCanvas.Children.Contains(fruit._ellipse))
    {
        myCanvas.Children.Remove(fruit._ellipse);
    }
}

十四、按键操作
通过方向键，设置Direct值即可。

private void MyCanvas_PreviewKeyDown(object sender, KeyEventArgs e)
{
    switch (e.Key)
    {
        case Key.Left:
            if (Direct != Direction.RIGHT)
            {
                Direct = Direction.LEFT;
            }
            break;

        case Key.Right:
            if (Direct != Direction.LEFT)
            {
                Direct = Direction.RIGHT;
            }
            break;

        case Key.Up:
            if (Direct != Direction.DOWN)
            {
                Direct = Direction.UP;
            }
            break;

        case Key.Down:
            if (Direct != Direction.UP)
            {
                Direct = Direction.DOWN;
            }
            break;

        case Key.Escape:
            Application.Current.Shutdown();
            break;

        case Key.Space:
            if (CurrGameState == GameState.NONE)
                return;

            if (CurrGameState == GameState.PAUSE)
            {
                CurrGameState = GameState.GAMEING;
                timer.Start();
                MenuControl_Pause.Header = "暂停";
            }
            else if (CurrGameState == GameState.GAMEING)
            {
                CurrGameState = GameState.PAUSE;
                timer.Stop();
                MenuControl_Pause.Header = "继续";
            }
            break;
    }
}

十四、定义开始游戏方法
先删除界面中的蛇身和水果（保留底部暗格），随机位置生成水果和三节蛇身。

private void StartGame()
{
    RemoveSnakeNodeAll();
    RemoveFruit();

    int startX = rnd.Next(5, CellWidth - 6);
    int startY = rnd.Next(5, CellHeight - 6);
    Direct = Direction.RIGHT;

    fruit = new Fruit(SetFruitToRandomPos(), myCanvas);

    SnakeNodes = new List<SnakeNode>();
    SnakeNodes.Add(new SnakeNode(new Point(startX, startY)));
    GenNewSnakeNode();
    GenNewSnakeNode();
}

十五、开始游戏菜单

调用StartGame()方法，并设定计时器开始。

private void MenuFile_NewGame_Click(object sender, RoutedEventArgs e)
{
    StartGame();
    timer.Start();
    CurrGameState = GameState.GAMEING;
    MenuControl_Pause.Header = "暂停";
}

十六、暂停与继续
直接上代码，没有要说的了。

private void MenuControl_Pause_Click(object sender, RoutedEventArgs e)
{
    if (CurrGameState == GameState.GAMEING)
    {
        CurrGameState = GameState.PAUSE;
        timer.Stop();
        MenuControl_Pause.Header = "继续";
    }
    else if (CurrGameState == GameState.PAUSE)
    {
        CurrGameState = GameState.GAMEING;
        timer.Start();
        MenuControl_Pause.Header = "暂停";
    }
}

十七、退出游戏

private void MenuFile_Exit_Click(object sender, RoutedEventArgs e)
{
    Application.Current.Shutdown();
}

十八、其他菜单功能
自己实现好了

private void MenuHelp_About_Click(object sender, RoutedEventArgs e)
{
}

[2019.12.23]更新：添加计时器事件代码（我不知道这个方法上次没有贴出来）

十九、计时器事件

/// <summary>
/// 计时器事件
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void Timer_Tick(object sender, EventArgs e)
{
    CheckCollision();
    GenNewSnakeNode();

    if (IsGameOver())
    {
        CurrGameState = GameState.STOP;
        timer.Stop();
        MessageBox.Show("游戏结束", "警告", MessageBoxButton.OK);

        return;
    }
}