由于以前看过外包的奇葩app，一个简单的app，几个viewcontroller居然可以内存飙到将近100M，简直是不忍直视，所以从那开始，自己每次写的代码，都会看，当控制器pop后是否会调delloc，或者看xcode的内存显示，严格要求自己。

typedef NS_ENUM(NSInteger, Direction) {
    leftDirection = 0,
    rightDirection,
};

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
        self.page = 0;
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    
    /////////////1.///////////////
    NSArray *colors = @[[UIColor redColor],[UIColor orangeColor],[UIColor purpleColor]];
    _scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, 320, 400)];
    _scrollView.pagingEnabled = YES;
    _scrollView.showsHorizontalScrollIndicator = NO;
    _scrollView.showsVerticalScrollIndicator = NO;
    
    
    float _x = 0;
    for (int i = 0; i < colors.count; i++) {
        UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0+_x, 0, 320, 400)];
        view.backgroundColor = colors[i];
        [_scrollView addSubview:view];
        
        _x += 320;
    }
    
    _scrollView.contentSize = CGSizeMake(_x, 0);
    [self.view addSubview:_scrollView];
    
    
    
    ///////////////2.//////////////////
    _timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(changeView) userInfo:nil repeats:YES];
    
}


-(void)changeView
{
    //修改页码
    if (self.page == 0) {
        self.switchDirection = rightDirection;
    }else if(self.page == 2){
        self.switchDirection = leftDirection;
    }
    if (self.switchDirection == rightDirection) {
        self.page ++;
    }else if (self.switchDirection == leftDirection){
        self.page --;
    }
    
    
    [_scrollView setContentOffset:CGPointMake(320*self.page, 0) animated:YES];
}

下面是容易忽略的部分，但是很重要，一旦不调用下面的方法，就算你的控制器pop了，也不会走delloc，你可以试试。

-(void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    [_timer invalidate];
}

由于的方法调用NSTimer，他会每隔一段时间去调用changeView的方法，在ARC中，如果你不把timer停掉，它是不会销毁的。