UIScrollView是個非常特殊的view，UIScrollView與其subview之間相對位置的約束,并不會直接用于frame的計算，而是會轉(zhuǎn)化為對ContentSize的計算。換句話說，當(dāng)UIScrollView知道了上下左右的約束分別指向subview什么位置之后，只要subview的位置固定下來了,ContentSize的大小就確定下來了。

@interface Example1Controller ()

@property (nonatomic, strong) UIScrollView *scrollView;
@property (nonatomic, strong) UIView *topView;
@property (nonatomic, strong) UIView *bottomView;
@property (nonatomic, strong) UIView *containView;

@end

@implementation Example1Controller

- (void)viewDidLoad {
    [super viewDidLoad];
    [self addPageSubviews];
    [self layoutPageSubviews];
}

- (void)addPageSubviews {
    [self.view addSubview:self.scrollView];
    [self.scrollView addSubview:self.containView];
    [self.containView addSubview:self.topView];
    [self.containView addSubview:self.bottomView];
}

- (void)layoutPageSubviews {
    
    [self.scrollView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.center.equalTo(self.view);
        make.width.mas_equalTo(300);
        make.height.mas_equalTo(300); 
    }];
    
    [self.containView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.edges.equalTo(self.scrollView);
        make.width.equalTo(self.scrollView);
//        make.height.equalTo(self.scrollView).multipliedBy(1.5);
    }];
    
    [self.topView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.equalTo(self.containView);
        make.leading.equalTo(self.containView);
        make.trailing.equalTo(self.containView);
        make.height.mas_equalTo(200);
    }];
    
    [self.bottomView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.equalTo(self.topView.mas_bottom);
        make.leading.equalTo(self.containView);
        make.trailing.equalTo(self.containView);
        make.height.mas_equalTo(200);
        make.bottom.equalTo(self.containView);
    }];
}

#pragma mark - getter & setter

-(UIView *)containView {
    if (!_containView) {
        _containView = [[UIView alloc] init];
        _containView.backgroundColor = [UIColor blueColor];
    }
    return _containView;
}

-(UIScrollView *)scrollView {
    if (!_scrollView) {
        _scrollView = [[UIScrollView alloc] init];
        _scrollView.backgroundColor = [UIColor redColor];
    }
    return _scrollView;
}

- (UIView *)topView {
    if (!_topView) {
        _topView = [[UIView alloc] init];
        _topView.backgroundColor = [UIColor grayColor];
    }
    return _topView;
}

-(UIView *)bottomView {
    if (!_bottomView) {
        _bottomView = [[UIView alloc] init];
        _bottomView.backgroundColor = [UIColor yellowColor];
    }
    return _bottomView;
}


@end