COCOS2D(4) 使用过渡场景在多个场景的切换
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。
-(void) onEnter { CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); // must call super here: [super onEnter]; } -(void) onEnterTransitionDidFinish { CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); // must call super here: [super onEnterTransitionDidFinish]; } -(void) onExit { CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); // must call super here: [super onExit]; }
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
#import <Foundation/Foundation.h> #import "cocos2d.h" typedef enum { TargetSceneINVALID = 0, TargetSceneFirstScene, TargetSceneOtherScene, TargetSceneMAX, } TargetScenes; @interface LoadingScene : CCScene { TargetScenes targetScene_; } +(id) sceneWithTargetScene:(TargetScenes)targetScene; -(id) initWithTargetScene:(TargetScenes)targetScene; @end
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
#import "LoadingScene.h" #import "MyFirstScene.h" #import "OtherScene.h" @interface LoadingScene (PrivateMethods) -(void) update:(ccTime)delta; @end @implementation LoadingScene +(id) sceneWithTargetScene:(TargetScenes)targetScene; { CCLOG(@"==========================================="); CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); // This creates an autorelease object of self (the current class: LoadingScene) return [[[self alloc] initWithTargetScene:targetScene] autorelease]; // Note: this does the exact same, it only replaced self with LoadingScene. The above is much more common. //return [[[LoadingScene alloc] initWithTargetScene:targetScene] autorelease]; } -(id) initWithTargetScene:(TargetScenes)targetScene { if ((self = [super init])) { targetScene_ = targetScene; CCLabelTTF* label = [CCLabelTTF labelWithString:@"Loading ..." fontName:@"Marker Felt" fontSize:64]; CGSize size = [[CCDirector sharedDirector] winSize]; label.position = CGPointMake(size.width / 2, size.height / 2); [self addChild:label]; // Must wait one frame before loading the target scene! // Two reasons: first, it would crash if not. Second, the Loading label wouldn't be displayed. [self scheduleUpdate]; } return self; } -(void) update:(ccTime)delta { // It's not strictly necessary, as we're changing the scene anyway. But just to be safe. [self unscheduleAllSelectors]; // Decide which scene to load based on the TargetScenes enum. // You could also use TargetScene to load the same with using a variety of transitions. switch (targetScene_) { case TargetSceneFirstScene: [[CCDirector sharedDirector] replaceScene:[MyFirstScene scene]]; break; case TargetSceneOtherScene: [[CCDirector sharedDirector] replaceScene:[OtherScene scene]]; break; default: // Always warn if an unspecified enum value was used. It's a reminder for yourself to update the switch // whenever you add more enum values. NSAssert2(nil, @"%@: unsupported TargetScene %i", NSStringFromSelector(_cmd), targetScene_); break; } // Tip: example usage of the INVALID and MAX enum values to iterate over all enum values for (TargetScenes i = TargetSceneINVALID + 1; i < TargetSceneMAX; i++) { } } -(void) dealloc { CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); // don't forget to call "super dealloc" [super dealloc]; } @end
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：
CCScene *newScene = [LoadingScene sceneWithTargetScene:TargetSceneOtherScene];
[[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：
2012-10-06 13:50:03.404 MutiScene[1884:1be03] =========================================== 2012-10-06 13:50:03.405 MutiScene[1884:1be03] scene: MyFirstScene 2012-10-06 13:50:03.406 MutiScene[1884:1be03] init : <MyFirstScene = 0x94e2540 | Tag = -1> 2012-10-06 13:50:08.610 MutiScene[1884:1be03] cocos2d: animation started with frame interval: 60.00 2012-10-06 13:50:08.613 MutiScene[1884:1be03] cocos2d: surface size: 480x320 2012-10-06 13:50:08.614 MutiScene[1884:1be03] onEnter: <MyFirstScene = 0x94e2540 | Tag = -1> 2012-10-06 13:50:08.615 MutiScene[1884:1be03] onEnterTransitionDidFinish: <MyFirstScene = 0x94e2540 | Tag = -1> 2012-10-06 13:50:11.844 MutiScene[1884:1be03] =========================================== 2012-10-06 13:50:11.845 MutiScene[1884:1be03] scene: OtherScene 2012-10-06 13:50:11.846 MutiScene[1884:1be03] init: <OtherScene = 0x9418280 | Tag = -1> 2012-10-06 13:50:16.907 MutiScene[1884:1be03] onEnter: <OtherScene = 0x9418280 | Tag = -1> 2012-10-06 13:50:19.944 MutiScene[1884:1be03] onExit: <MyFirstScene = 0x94e2540 | Tag = -1> 2012-10-06 13:50:19.945 MutiScene[1884:1be03] onEnterTransitionDidFinish: <OtherScene = 0x9418280 | Tag = -1> 2012-10-06 13:50:19.947 MutiScene[1884:1be03] dealloc : <MyFirstScene = 0x94e2540 | Tag = -1> 2012-10-06 13:50:29.953 MutiScene[1884:1be03] =========================================== 2012-10-06 13:50:29.954 MutiScene[1884:1be03] sceneWithTargetScene:: LoadingScene 2012-10-06 13:50:29.961 MutiScene[1884:1be03] onExit: <OtherScene = 0x9418280 | Tag = -1> 2012-10-06 13:50:29.962 MutiScene[1884:1be03] dealloc: <OtherScene = 0x9418280 | Tag = -1> 2012-10-06 13:50:29.977 MutiScene[1884:1be03] =========================================== 2012-10-06 13:50:29.979 MutiScene[1884:1be03] scene: MyFirstScene 2012-10-06 13:50:29.980 MutiScene[1884:1be03] init : <MyFirstScene = 0x9418280 | Tag = -1> 2012-10-06 13:50:35.031 MutiScene[1884:1be03] dealloc: <LoadingScene = 0x11a59950 | Tag = -1> 2012-10-06 13:50:35.032 MutiScene[1884:1be03] onEnter: <MyFirstScene = 0x9418280 | Tag = -1> 2012-10-06 13:50:35.032 MutiScene[1884:1be03] onEnterTransitionDidFinish: <MyFirstScene = 0x9418280 | Tag = -1>
