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原理：UIScrollView 繼承于UIView，通過(guò)添加手勢(shì)來(lái)改變bounds.origin的位置來(lái)實(shí)現(xiàn)滾動(dòng)的效果。

提到這里我們可以來(lái)區(qū)分一下bounds與frame的區(qū)別

bounds：根據(jù)自身的坐標(biāo)系來(lái)設(shè)置位置和大小，當(dāng)我們改變父視圖的bounds.origin時(shí)會(huì)發(fā)現(xiàn)父視圖沒有變化，但子視圖的位置卻發(fā)生了改變.
frame：根據(jù)父視圖的坐標(biāo)系來(lái)設(shè)置位置和大小。

滑動(dòng)

上線滑動(dòng)實(shí)際是我們改變父視圖的bounds.origin.y、左右滑動(dòng)我們只需要改變父視圖的bounds.origin.x，子視圖中的試圖就會(huì)出現(xiàn)滑動(dòng)的效果。讓我們用代碼來(lái)說(shuō)話吧：

#import "ZYScrollView.h"

@implementation ZYScrollView
- (instancetype)initWithFrame:(CGRect)frame{
    self = [super initWithFrame:frame];
    if(self){
        UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(panAction:)];
        [self addGestureRecognizer:pan];
    }
    return self;
}
- (void)panAction:(UIPanGestureRecognizer *)pan {
    switch (_type) {
        case ScrollViewUpandDown:{//上下滑動(dòng)（我們只需要獲取它的Y軸偏移量）
            // 獲取手指的偏移量
            CGPoint transY = [pan translationInView:pan.view];
            // 修改bounds
            CGRect bounds = self.bounds;
            bounds.origin.y -= transY.y;
            self.bounds = bounds;
            // 復(fù)位
            [pan setTranslation:CGPointZero inView:pan.view];
            break;
        }
            
        default:{//左右滑動(dòng)（我們只需要獲取它的X軸的偏移量即可）
             // 獲取手指的偏移量
            CGPoint transX = [pan translationInView:pan.view];
            CGRect bounds = self.bounds;
            bounds.origin.x -= transX.x;
            self.bounds = bounds;
            [pan setTranslation:CGPointZero inView:pan.view];
            break;
        }
    }
}

具體的實(shí)現(xiàn)

#import "ScrollViewController.h"
#import "ZYScrollView.h"
@interface ScrollViewController ()
@property (nonatomic, strong) ZYScrollView * upScrollView;
@property (nonatomic, strong) ZYScrollView * aboutScrollView;
@end

@implementation ScrollViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    self.upScrollView = [[ZYScrollView alloc] initWithFrame:CGRectMake(0, 0, YSCREEN_WIDTH, YSCREEN_HEIGHT/2)];
    self.upScrollView.type = ScrollViewUpandDown;
    [self.view addSubview:self.upScrollView];
    self.aboutScrollView = [[ZYScrollView alloc] initWithFrame:CGRectMake(0, YSCREEN_HEIGHT/2, YSCREEN_WIDTH, YSCREEN_HEIGHT/2)];
    self.aboutScrollView.type = ScrollViewabout;
    [self.view addSubview:self.aboutScrollView];
    UIView * redView = [[UIView alloc] initWithFrame:CGRectMake(50, 100, 100, 100)];
    redView.backgroundColor = [UIColor redColor];
    [self.upScrollView addSubview:redView];
    UIView * blueView = [[UIView alloc] initWithFrame:CGRectMake(50, 100, 100, 100)];
    blueView.backgroundColor = [UIColor blueColor];
    [self.aboutScrollView addSubview:blueView];
}
@end

這樣我們基本就完成視圖的滑動(dòng)，還有很多可以改進(jìn)與優(yōu)化的地方這里只是簡(jiǎn)單的向大家展示了UIScrollView的滑動(dòng)原理。