bounds的深入研究

#import "ViewController.h"

@interface ViewController ()<UIScrollViewDelegate>

@property (weak, nonatomic)  UIView *scrollView
@property (nonatomic, assign) CGPoint offsetX;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    UIView *scrollView = [[UIView alloc] initWithFrame:self.view.bounds];
    [self.view addSubview:scrollView];
    _scrollView = scrollView;  
    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
    [scrollView addGestureRecognizer:pan];
    UISwitch *switchV = [[UISwitch alloc] init];
    [scrollView addSubview:switchV];   
}

// 拖动的时候调用
- (void)pan:(UIPanGestureRecognizer *)pan
{
    // 获取偏移量
    CGPoint transP = [pan translationInView:pan.view];
    _offsetX.x += -transP.x;
    _offsetX.y += -transP.y;  
    _scrollView.bounds = CGRectMake(_offsetX.x, _offsetX.y, self.view.bounds.size.width, self.view.bounds.size.height);    
    [pan setTranslation:CGPointZero inView:pan.view];
    
}