Android實例剖析筆記（五）

作者: Phinecos(洞庭散人) 來源: 博客園發布時間: 2010-10-24 22:55 閱讀: 2071 次推薦: 0 原文鏈接 [收藏]

摘要：介紹Android sdk中自帶的第二個示例程序—Snake（貪食蛇）

　　游戲暫停/繼續機制

由于原來的代碼中在游戲運行時沒有提供控制選項（比如暫停/繼續），因此除非你死了，否則只能玩到底。我這里對代碼進行一些修改，加入一個Option Menu來提供暫停/繼續機制。

首先加入一個變量記錄游戲當前狀態

private int mState = SnakeView.READY;

然后重載onCreateOptionsMenu函數，創建一個控制菜單項，并對其進行處理，提供暫停/繼續機制。

   /*
     * @see android.app.Activity#onOptionsItemSelected(android.view.MenuItem)
     * @Author:phinecos
     * @Date:2009-08-28
     */
    @Override
    public boolean onOptionsItemSelected(MenuItem item)
    {
        switch (item.getItemId())
        {
            case MENU_CONTROL:
            {
                if (mState == SnakeView.PAUSE)
                {//此前狀態是"停止"，則轉為"運行"
                    mState = SnakeView.RUNNING;
                    mSnakeView.setMode(SnakeView.RUNNING);
                    item.setIcon(android.R.drawable.ic_media_pause).setTitle(R.string.cmd_pause);
                }
                else if(mState == SnakeView.RUNNING)
                {//此前狀態是"運行",則轉為“暫停"
                    mState = SnakeView.PAUSE;
                    mSnakeView.setMode(SnakeView.PAUSE);
                    item.setIcon(android.R.drawable.ic_media_play).setTitle(R.string.cmd_run);
                }
                else if(mState == SnakeView.READY)
                {//此前是"初始狀態"，則轉為"運行"
                    mState = SnakeView.RUNNING;
                }
    return true;
            }
        }
        return super.onOptionsItemSelected(item);
    }
    /*
     * @see android.app.Activity#onOptionsItemSelected(android.view.MenuItem)
     * @Author:phinecos
     * @Date:2009-08-28
     */
    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
         super.onCreateOptionsMenu(menu);
         menu.add(0, MENU_CONTROL, 0, R.string.cmd_pause).setIcon(android.R.drawable.ic_media_pause);
         return true;
    }

　　修改后運行截圖如下：

　　當然，這段代碼還是有問題的，游戲剛開始時，必須先點擊菜單確認，再按上方向鍵才能開始。（以后再來修改。。。）

　　穿墻貪食蛇

第二個修改是把這個普通的貪食蛇改成可以穿墻(呵呵，這樣就可以不死了。。。)。想必要修改的就是撞墻檢測那段代碼？沒錯，就是下面這段！

// Collision detection
// For now we have a 1-square wall around the entire arena
if ((newHead.x < 1) || (newHead.y < 1) || (newHead.x > mXTileCount - 2)|| (newHead.y > mYTileCount - 2))
{//撞墻
setMode(LOSE);
return;
}

　　原來的版本是發現撞墻時就直接判定為失敗，我這里做個小小的修改，讓它可以穿墻而去:

private void updateSnake()
    {
        boolean growSnake = false;

        // grab the snake by the head
        Coordinate head = mSnakeTrail.get(0);
        Coordinate newHead = new Coordinate(1, 1);

        mDirection = mNextDirection;

        switch (mDirection)
        {
        case EAST:
        {
            newHead = new Coordinate(head.x + 1, head.y);
            break;
        }
        case WEST:
        {
            newHead = new Coordinate(head.x - 1, head.y);
            break;
        }
        case NORTH:
        {
            newHead = new Coordinate(head.x, head.y - 1);
            break;
        }
        case SOUTH:
        {
            newHead = new Coordinate(head.x, head.y + 1);
            break;
        }
        }

        //穿墻的處理
        if (newHead.x == 0)
        {//穿左邊的墻
            newHead.x = mXTileCount - 2;
        }
        else if (newHead.y == 0)
        {//穿上面的墻
            newHead.y = mYTileCount - 2;
        }
        else if (newHead.x == mXTileCount - 1)
        {//穿右邊的墻
            newHead.x = 1;
        }
        else if (newHead.y == mYTileCount - 1)
        {//穿下面的墻
            newHead.y = 1;
        }
        // 判斷是否撞到自己
        int snakelength = mSnakeTrail.size();
        for (int snakeindex = 0; snakeindex < snakelength; snakeindex++)
        {
            Coordinate c = mSnakeTrail.get(snakeindex);
            if (c.equals(newHead))
            {
                setMode(LOSE);
                return;
            }
        }
        // 判斷是否吃掉“蘋果”
        int applecount = mAppleList.size();
        for (int appleindex = 0; appleindex < applecount; appleindex++)
        {
            Coordinate c = mAppleList.get(appleindex);
            if (c.equals(newHead))
            {
                mAppleList.remove(c);
                addRandomApple();
                mScore++;
                mMoveDelay *= 0.9;
                growSnake = true;
            }
        }
        // push a new head onto the ArrayList and pull off the tail
        mSnakeTrail.add(0, newHead);
        // except if we want the snake to grow
        if (!growSnake)
        {
            mSnakeTrail.remove(mSnakeTrail.size() - 1);
        }
        int index = 0;
        for (Coordinate c : mSnakeTrail)
        {
            if (index == 0)
            {
                setTile(YELLOW_STAR, c.x, c.y);
            }
            else
            {
                setTile(RED_STAR, c.x, c.y);
            }
            index++;
        }
}

　　其實修改后的代碼非常簡單，就是把新節點的值做些處理，讓它移動到對應的行/列的頭部或尾部即可。下面就是修改后的“穿墻”貪食蛇的運行截圖：

　　全屏機制