现在来实现敌机类

敌机和我方飞机相似，具有生命值、能够发射子弹，并且有自己的运动轨迹。其实可以为它们设计一个共同的基类，这样可以更方便扩展。

不同的敌机，应设置不同的标识、属性

// 敌机生命值
const int ENEMY1_MAXLIFE = 1;
const int ENEMY2_MAXLIFE = 2;
const int ENEMY3_MAXLIFE = 5;
const int ENEMY4_MAXLIFE = 10;

// 敌机分数
const int ENEMY1_score = 1;
const int ENEMY2_score = 6;
const int ENEMY3_score = 20;
const int ENEMY4_score = 50;

// 敌机类型
enum EnemyType
{
	Enemy1 = 1,Enemy2,Enemy3,Enemy4,};

void setEnemyByType(EnemyType enType);
Sprite* getSprite();

int getLife();
void loseLife();
Rect getBoundingBox();

void Enemy::setEnemyByType(EnemyType enType)
{
	switch (enType)
	{
	case Enemy1:
		pEnemySprite = Sprite::createWithSpriteFrame(SpriteFrameCache::getInstance()->getSpriteFrameByName("enemy1.png"));
		nLife = ENEMY1_MAXLIFE;
		break;
	case Enemy2:
		pEnemySprite = Sprite::createWithSpriteFrame(SpriteFrameCache::getInstance()->getSpriteFrameByName("enemy2.png"));
		nLife = ENEMY2_MAXLIFE;
		break;
	case Enemy3:
		pEnemySprite = Sprite::createWithSpriteFrame(SpriteFrameCache::getInstance()->getSpriteFrameByName("enemy3.png"));
		nLife = ENEMY3_MAXLIFE;
		break;
	case Enemy4:
		pEnemySprite = Sprite::createWithSpriteFrame(SpriteFrameCache::getInstance()->getSpriteFrameByName("enemy4.png"));
		nLife = ENEMY4_MAXLIFE;
		break;
	default:
		return;
		break;
	}

	this->addChild(pEnemySprite);
	Size winSize = Director::getInstance()->getWinSize();
	Size enemySize = pEnemySprite->getContentSize();
	int minX = enemySize.width / 2;
	int maxX = winSize.width - enemySize.width / 2;
	int rangeX = maxX - minX;
	int actualX = (rand() % rangeX) + minX;

	// 设置敌机Node方位 Node包含Sprite
	this->setPosition(Point(actualX,winSize.height - enemySize.height / 2));
}

bool Enemy::init()
{
	bool pRet = true;
	if (!Node::init())
	{
		pRet = false;
	}

	return pRet;
}

Sprite* Enemy::getSprite()
{
	return pEnemySprite;
}

int Enemy::getLife()
{
	return nLife;
}

void Enemy::loseLife()
{
	--nLife;
}

Rect Enemy::getBoundingBox()
{
	Rect rect = pEnemySprite->boundingBox();
	Point pos = this->convertToWorldSpace(rect.origin);
	Rect enemyRect(pos.x,pos.y,rect.size.width,rect.size.height);
	return enemyRect;
}