cocos2d中晃动手机切换scene(有切换特效),有时崩溃,求解

cocos2d中晃动手机切换scene(有切换特效),有时崩溃,求解

如题,两个scene互相切换,晃动手机我用的是

-(id) init{ if ((self = [super init])) {

         //blablabla

[[UIAccelerometersharedAccelerometer] setUpdateInterval:1/60];
[[UIAccelerometersharedAccelerometer] setDelegate:self];}}

- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {
    
static NSInteger shakeCount = 0;
static NSDate *shakeStart;

NSDate *now = [[NSDate alloc] init];
NSDate *checkDate = [[NSDate alloc] initWithTimeInterval:1.5f sinceDate:shakeStart];

if ([now compare:checkDate] == NSOrderedDescending || shakeStart == nil){
shakeCount = 0;
[shakeStart release];
shakeStart = [[NSDate alloc] init];}

[now release];
[checkDate release];

if (fabsf(acceleration.x) > 2.0 || fabsf(acceleration.y) > 2.0 || fabsf(acceleration.z) > 2.0){
shakeCount++;
if (shakeCount > 2) {

CCTransitionFade* newScene = [CCTransitionFadetransitionWithDuration:2scene:[FirstScenescene] withColor:ccBLACK]; 
            [[CCDirector sharedDirector] replaceScene:newScene];

 shakeCount = 0;
[shakeStart release];
shakeStart = [[NSDate alloc] init];}}}

有时可以切换成功,有时候就崩溃