使用过渡场景在多个场景的切换COCOS2D(4)

CCNode有三个方法，使用CCDirector的replaceScene方法替换场景时，每个节点都会调用这三个方法：

onEnter与onExit方法在改变场景过程中的特定时刻被调用，这取决于是否使用CCTransitionScene。

onEnterTransitionDidFinish方法在替换结束时调用。

必须总是调用这些方法的超类实现来避免难输入问题和内存泄漏。

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-(void) onEnter 

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{ 

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    CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); 

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    // must call super here: 

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    [super onEnter]; 

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} 

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-(void) onEnterTransitionDidFinish 

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{ 

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    CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); 

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    // must call super here: 

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    [super onEnterTransitionDidFinish]; 

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} 

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-(void) onExit 

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{ 

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    CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); 

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    // must call super here: 

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    [super onExit]; 

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}

编写过渡场景：

LoadingScene充当一个中间场景的角色，它是cocos2d中的CCScene类的派生类，不必为每一次场景创建一个新的LoadingScene。

代码清单：LoadingScene.h

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#import <Foundation/Foundation.h> 

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#import "cocos2d.h" 

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typedef enum 

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{ 

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    TargetSceneINVALID = 0, 

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    TargetSceneFirstScene, 

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    TargetSceneOtherScene, 

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    TargetSceneMAX, 

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} TargetScenes; 

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<a href="http://my.oschina.net/interface" class="referer" target="_blank">@interface</a>  LoadingScene : CCScene { 

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    TargetScenes targetScene_; 

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} 

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+(id) sceneWithTargetScene:(TargetScenes)targetScene; 

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-(id) initWithTargetScene:(TargetScenes)targetScene; 

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<a href="http://my.oschina.net/u/567204" class="referer" target="_blank">@end</a>

使用enum给各个场景编个号，而且将enum的第一个值设为0,在Objective－c中变量的值会自动初始化为0.并在最后设了个MAX值。

代码清单：LoadingScene.m

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 #import "LoadingScene.h" 
 
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 #import "MyFirstScene.h" 
 
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 #import "OtherScene.h" 
 
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 <a href="http://my.oschina.net/interface" class="referer" target="_blank">@interface</a>  LoadingScene (PrivateMethods) 
 
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 -(void) update:(ccTime)delta; 
 
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 <a href="http://my.oschina.net/u/567204" class="referer" target="_blank">@end</a>  
 
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 @implementation LoadingScene 
 
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 +(id) sceneWithTargetScene:(TargetScenes)targetScene; 
 
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 { 
 
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     CCLOG(@"==========================================="); 
 
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     CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); 
 
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     // This creates an autorelease object of self (the current class: LoadingScene) 
 
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     return [[[self alloc] initWithTargetScene:targetScene] autorelease]; 
 
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     // Note: this does the exact same, it only replaced self with LoadingScene. The above is much more common. 
 
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     //return [[[LoadingScene alloc] initWithTargetScene:targetScene] autorelease]; 
 
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 } 
 
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 -(id) initWithTargetScene:(TargetScenes)targetScene 
 
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 { 
 
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     if ((self = [super init])) 
 
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     { 
 
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         targetScene_ = targetScene; 
 
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         CCLabelTTF* label = [CCLabelTTF labelWithString:@"Loading ..." fontName:@"Marker Felt" fontSize:64]; 
 
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         CGSize size = [[CCDirector sharedDirector] winSize]; 
 
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         label.position = CGPointMake(size.width / 2, size.height / 2); 
 
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         [self addChild:label]; 
 
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         // Must wait one frame before loading the target scene! 
 
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         // Two reasons: first, it would crash if not. Second, the Loading label wouldn't be displayed. 
 
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         [self scheduleUpdate]; 
 
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     } 
 
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     return self; 
 
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 } 
 
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 -(void) update:(ccTime)delta 
 
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 { 
 
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     // It's not strictly necessary, as we're changing the scene anyway. But just to be safe. 
 
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     [self unscheduleAllSelectors]; 
 
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     // Decide which scene to load based on the TargetScenes enum. 
 
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     // You could also use TargetScene to load the same with using a variety of transitions. 
 
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     switch (targetScene_) 
 
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     { 
 
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         case TargetSceneFirstScene: 
 
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             [[CCDirector sharedDirector] replaceScene:[MyFirstScene scene]]; 
 
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             break; 
 
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         case TargetSceneOtherScene: 
 
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             [[CCDirector sharedDirector] replaceScene:[OtherScene scene]]; 
 
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             break; 
 
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         default: 
 
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             // Always warn if an unspecified enum value was used. It's a reminder for yourself to update the switch 
 
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             // whenever you add more enum values. 
 
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             NSAssert2(nil, @"%@: unsupported TargetScene %i", NSStringFromSelector(_cmd), targetScene_); 
 
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             break; 
 
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     } 
 
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     // Tip: example usage of the INVALID and MAX enum values to iterate over all enum values 
 
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     for (TargetScenes i = TargetSceneINVALID + 1; i < TargetSceneMAX; i++) 
 
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     { 
 
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     } 
 
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 } 
 
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 -(void) dealloc 
 
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 { 
 
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     CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); 
 
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     // don't forget to call "super dealloc" 
 
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     [super dealloc]; 
 
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 } 
 
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 <a href="http://my.oschina.net/u/567204" class="referer" target="_blank">@end</a>

由于LoadingScene类由CCScene派生出来，所以不需要调用［CCScene node］，sceneWithTargetScene方法先为self分配空间，然后调用initWithTargetScene初始化。

在MyFirstScene中调用LoadingScene：

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 CCScene *newScene = [LoadingScene sceneWithTargetScene:TargetSceneOtherScene]; 
 
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 [[CCDirector sharedDirector] replaceScene:newScene];

在OtherScene中调用基本类似，请读者自行实践。

下面给出了在执行过程中的一些输出信息，它详细的说明了各个方法的调用顺序：

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 01
 2012-10-06 13:50:03.404 MutiScene[1884:1be03] =========================================== 
 
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 2012-10-06 13:50:03.405 MutiScene[1884:1be03] scene: MyFirstScene 
 
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 2012-10-06 13:50:03.406 MutiScene[1884:1be03] init : <MyFirstScene = 0x94e2540 | Tag = -1> 
 
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 2012-10-06 13:50:08.610 MutiScene[1884:1be03] cocos2d: animation started with frame interval: 60.00 
 
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 2012-10-06 13:50:08.613 MutiScene[1884:1be03] cocos2d: surface size: 480x320 
 
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 2012-10-06 13:50:08.614 MutiScene[1884:1be03] onEnter: <MyFirstScene = 0x94e2540 | Tag = -1> 
 
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 2012-10-06 13:50:08.615 MutiScene[1884:1be03] onEnterTransitionDidFinish: <MyFirstScene = 0x94e2540 | Tag = -1> 
 
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 2012-10-06 13:50:11.844 MutiScene[1884:1be03] =========================================== 
 
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 2012-10-06 13:50:11.845 MutiScene[1884:1be03] scene: OtherScene 
 
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 2012-10-06 13:50:11.846 MutiScene[1884:1be03] init: <OtherScene = 0x9418280 | Tag = -1> 
 
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 2012-10-06 13:50:16.907 MutiScene[1884:1be03] onEnter: <OtherScene = 0x9418280 | Tag = -1> 
 
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 2012-10-06 13:50:19.944 MutiScene[1884:1be03] onExit: <MyFirstScene = 0x94e2540 | Tag = -1> 
 
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 2012-10-06 13:50:19.945 MutiScene[1884:1be03] onEnterTransitionDidFinish: <OtherScene = 0x9418280 | Tag = -1> 
 
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 2012-10-06 13:50:19.947 MutiScene[1884:1be03] dealloc : <MyFirstScene = 0x94e2540 | Tag = -1> 
 
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 2012-10-06 13:50:29.953 MutiScene[1884:1be03] =========================================== 
 
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 2012-10-06 13:50:29.954 MutiScene[1884:1be03] sceneWithTargetScene:: LoadingScene 
 
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 2012-10-06 13:50:29.961 MutiScene[1884:1be03] onExit: <OtherScene = 0x9418280 | Tag = -1> 
 
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 2012-10-06 13:50:29.962 MutiScene[1884:1be03] dealloc: <OtherScene = 0x9418280 | Tag = -1> 
 
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 2012-10-06 13:50:29.977 MutiScene[1884:1be03] =========================================== 
 
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 2012-10-06 13:50:29.979 MutiScene[1884:1be03] scene: MyFirstScene 
 
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 2012-10-06 13:50:29.980 MutiScene[1884:1be03] init : <MyFirstScene = 0x9418280 | Tag = -1> 
 
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 2012-10-06 13:50:35.031 MutiScene[1884:1be03] dealloc: <LoadingScene = 0x11a59950 | Tag = -1> 
 
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 2012-10-06 13:50:35.032 MutiScene[1884:1be03] onEnter: <MyFirstScene = 0x9418280 | Tag = -1> 
 
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 2012-10-06 13:50:35.032 MutiScene[1884:1be03] onEnterTransitionDidFinish: <MyFirstScene = 0x9418280 | Tag = -1>