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 valuesfor (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: MyFirstScene2012-10-06 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: 60.002012-10-06 13:50:08.613 MutiScene[1884:1be03] cocos2d: surface size: 480x3202012-10-06 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: OtherScene2012-10-06 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:: LoadingScene2012-10-06 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: MyFirstScene2012-10-06 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>