void addTarget()函数将会帮我们完成这一工作，敌人将会以随机的速度，从游戏场景左移动到右。
在HelloWorldScence.h里声明void addTarget()，并在HelloWorldScene.cpp里添加以下的代码，(请不要忘记在HelloWorldScene.cpp的开头加入using namespace cocos2d)
1// cpp with cocos2d-x
2void HelloWorld::addTarget()
3{
4 CCSprite *target = CCSprite::spriteWithFile("Target.png",
5 CCRectMake(0,0,27,40) );
6
7 // Determine where to spawn the target along the Y axis
8 CCSize winSize = CCDirector::sharedDirector()->getWinSize();
9 int minY = target->getContentSize().height/2;
10 int maxY = winSize.height
11 - target->getContentSize().height/2;
12 int rangeY = maxY - minY;
13 // srand( TimGetTicks() );
14 int actualY = ( rand() % rangeY ) + minY;
15
16 // Create the target slightly off-screen along the right edge,
17 // and along a random position along the Y axis as calculated
18 target->setPosition(
19 ccp(winSize.width + (target->getContentSize().width/2),
20 actualY) );
21 this->addChild(target);
22
23 // Determine speed of the target
24 int minDuration = (int)2.0;
25 int maxDuration = (int)4.0;
26 int rangeDuration = maxDuration - minDuration;
27 // srand( TimGetTicks() );
28 int actualDuration = ( rand() % rangeDuration )
29 + minDuration;
30
31 // Create the actions
32 CCFiniteTimeAction* actionMove =
33 CCMoveTo::actionWithDuration( (ccTime)actualDuration,
34 ccp(0 - target->getContentSize().width/2, actualY) );
35 CCFiniteTimeAction* actionMoveDone =
36 CCCallFuncN::actionWithTarget( this,
37 callfuncN_selector(HelloWorld::spriteMoveFinished));
38 target->runAction( CCSequence::actions(actionMove,
39 actionMoveDone, NULL) );
40}
1// objc with cocos2d-iphone
2-(void)addTarget
3{
4 CCSprite *target = [CCSprite spriteWithFile:@"Target.png"
5 rect:CGRectMake(0, 0, 27, 40)];
6
7 // Determine where to spawn the target along the Y axis
8 CGSize winSize = [[CCDirector sharedDirector] winSize];
9 int minY = target.contentSize.height/2;
10 int maxY = winSize.height - target.contentSize.height/2;
11 int rangeY = maxY - minY;
12
13 int actualY = (arc4random() % rangeY) + minY;
14
15 // Create the target slightly off-screen along the right edge,
16 // and along a random position along the Y axis as calculated
17 target.position =
18 ccp(winSize.width + (target.contentSize.width/2),
19 actualY);
20 [self addChild:target];
21
22 // Determine speed of the target
23 int minDuration = 2.0;
24 int maxDuration = 4.0;
25 int rangeDuration = maxDuration - minDuration;
26
27 int actualDuration = (arc4random() % rangeDuration)
28 + minDuration;
29
30 // Create the actions
31 id actionMove =
32 [CCMoveTo actionWithDuration:actualDuration
33 position:ccp(-target.contentSize.width/2, actualY)];
34 id actionMoveDone =
35 [CCCallFuncN actionWithTarget:self
36 selector:@selector(spriteMoveFinished:)];
37 [target runAction:[CCSequence actions:actionMove,
38 actionMoveDone, nil]];
39}
这里用callfuncN_selector(HelloWorld::spriteMoveFinished)回调了spriteMoveFinished方法，我们需要在HelloWorldScene.h里声明并如下来定义它，
1// cpp with cocos2d-x
2void HelloWorld::spriteMoveFinished(CCNode* sender)
3{
4 CCSprite *sprite = (CCSprite *)sender;
5 this->removeChild(sprite, true);
6}
1// objc with cocos2d-iphone
2-(void)spriteMoveFinished:(id)sender
3{
4 CCSprite *sprite = (CCSprite *)sender;
5 [self removeChild:sprite cleanup:YES];
6}
要点
1. 关于随机函数。srand和rand是C标准库函数。对于每一个平台来说，你可以先获取毫秒级时间来得到一个随机数。在沃Phone上，这个函数是TimGetTickes()，而在iPhone上，你可以直接通过arc4random()函数来获得随机数。
2. Objc中的YES和NO，在cpp中变为true和false。
3. 回调函数，在objc中用selector:@selector(spriteMoveFinished)，但在cpp中实现就比较复杂了，你可以参考cocos2dx\include\selector_protocol.h里的声明。一共有5种回调函数类型
schedule_selector
callfunc_selector
callfuncN_selector
callfuncND_selector
menu_selector
如何使用它们，根据所用函数的定义来决定。比如使用CCTimer::initWithTarget函数，它的第二个参数是SEL_SCHEDULE类型，到selector_protocol.h里查一下，可以看到对应的是schedule_selector(_SELECTOR)宏，所以调用时就需要在类里头实现一个void MyClass::MyCallbackFuncName(ccTime)函数，然后把schedule_selector(MyClass::MyCallbackFuncName)作为CCTimer::initWithTarget的第二个参数传入。
之后，我们应该定时地为游戏加入敌人，把以下代码加入到init()函数的返回值前。
1// cpp with cocos2d-x
2// Call game logic about every second
3this->schedule( schedule_selector(HelloWorld::gameLogic), 1.0 );
1// objc with cocos2d-iphone
2// Call game logic about every second
3[self schedule:@selector(gameLogic:) interval:1.0];
然后在HelloWorldScence.cpp里实现gameLogic()。请注意gameLogic()应该声明为pubilc，否则是无法回调的。
1// cpp with cocos2d-x
2void HelloWorld::gameLogic(ccTime dt)
3{
4 this->addTarget();
5}
1// objc with cocos2d-iphone
2-(void)gameLogic:(ccTime)dt
3{
4 [self addTarget];
5}
好了，所有事情都做完了，编译并运行，好好享用你的成果。
iPhone
Android
沃Phone
Win32
