抽屉效果代码

// ViewController.h
#import <UIKit/UIKit.h>

@interface ViewController : UIViewController


@end

// ViewController.m
#import "ViewController.h"

#define targetR 250
#define targetL -250

#define screenW [UIScreen mainScreen].bounds.size.width
#define screenH [UIScreen mainScreen].bounds.size.height

@interface ViewController ()

/** 红色的view*/
@property (nonatomic, weak) UIView *mainView;
/** 左边的view*/
@property (nonatomic, weak) UIView *leftView;
/** 右边的view*/
@property (nonatomic, weak) UIView *rightView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    // 添加子视图
    [self addViews];
    // 给self.view添加一个手势
    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tap:)];
    [self.view addGestureRecognizer:tap];
}

- (void)tap:(UITapGestureRecognizer *)tap
{

    [UIView animateWithDuration:0.5 animations:^{
        self.mainView.frame = self.view.bounds;
    }];
}

// 添加子视图
- (void)addViews
{
    // 创建一个蓝色view
    UIView *blueView = [[UIView alloc] init];
    blueView.frame = self.view.bounds;
    blueView.backgroundColor = [UIColor blueColor];
    self.leftView = blueView;
    [self.view addSubview:blueView];

    // 创建一个绿色view
    UIView *greenView = [[UIView alloc] init];
    greenView.frame = self.view.bounds;
    greenView.backgroundColor = [UIColor greenColor];
    self.rightView = greenView;
    [self.view addSubview:greenView];

    // 创建一个红色view
    UIView *mainView = [[UIView alloc] init];
    mainView.frame = self.view.bounds;
    mainView.backgroundColor = [UIColor redColor];
    self.mainView = mainView;
    [self.view addSubview:mainView];
    // 给mainView添加拖动手势
    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
    [self.mainView addGestureRecognizer:pan];
}

// 拖动手势
- (void)pan:(UIPanGestureRecognizer *)pan
{
    // 拿到手势当前点,pan.view就是self.mainView
    CGPoint transP = [pan translationInView:pan.view];

    pan.view.transform = CGAffineTransformTranslate(pan.view.transform, transP.x, transP.y);

    //根据传入的偏移量计算self.mainV的frame
    self.mainView.frame = [self frameWithOffset:transP.x];

    if (self.mainView.frame.origin.x > 0) {
        self.rightView.hidden = YES;
    } else if (self.mainView.frame.origin.x < 0) {
        self.rightView.hidden = NO;
    }

    // 拖动过程没有松开手指，所以不会调用下面的方法，但是self.mainView的尺寸一直在改变
    // 所以传人到里面的self.mainView也是改变了的
    if (pan.state == UIGestureRecognizerStateEnded) {
        CGFloat target = 0;
        // 下面两种情况才会改变target的值，其他情况target都为0
        // 比如self.mainView.frame.origin.x < screenW * 0.5
        // 比如 CGRectGetMaxX(self.mainView.frame) > screenW * 0.5
        if (self.mainView.frame.origin.x > screenW * 0.5) {
            target = targetR;
        } else if (CGRectGetMaxX(self.mainView.frame) < screenW * 0.5) {
            target = targetL;
        }

        CGFloat offset = target - self.mainView.frame.origin.x;
        // 同样根据传入的偏移量计算self.mainV的frame
        [UIView animateWithDuration:0.5 animations:^{
            self.mainView.frame = [self frameWithOffset:offset];
        }];

    }

    //复位
    [pan setTranslation:CGPointZero inView:pan.view];
}

//根据传入的偏移量计算self.mainV的frame
- (CGRect)frameWithOffset:(CGFloat)offset
{
    CGRect frame = self.mainView.frame;
    // offset刚刚自己打印了一些，就是连续输出一串0.5。。。。1。。。很小的一些数
    // 所以要想真正获得self.mainView的真正位置，必须
    frame.origin.x += offset;

    frame.origin.y = fabs(100 * frame.origin.x / screenW);
    frame.size.height = screenH - 2 * frame.origin.y;

    return frame;
}

@end
程序一开始效果图片:
红色view的x大于屏幕宽度的一半后显示的效果图片:
红色view的x小于屏幕宽度的一半后显示的效果图片:
抽屉效果代码

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