抽屉效果的实现

//
//  ViewController.m
//  抽屉效果
//
//  Created by wtw on 15/7/20.
//  Copyright (c) 2015年 wtw. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic,weak) UIView *leftView;
@property (nonatomic,weak) UIView *rightView;
@property (nonatomic,weak) UIView *mainView;
//复位，定位后点击后会复位
@property (nonatomic,assign) BOOL isDraging;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //添加子控件
    [self addchildview];
    
    //时刻监听主视图frame的改变
    /**
     *  以后如果需要时刻监听对象的某个属性的改变，就用KVO
     *  给mainView添加一个观察者
     *  addObserver:观察者
     *  forKeyPath：需要监听的属性
     *  options:监听新值的改变
     */
    [self.mainView addObserver:self forKeyPath:@"frame" options:NSKeyValueObservingOptionNew context:nil];
}
    //只要监听的属性以改变就会调用
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    //NSLog(@"%@",NSStringFromCGRect(self.mainView.frame));
    
    if (self.mainView.frame.origin.x < 0) {
        //显示右边，隐藏左边
        self.rightView.hidden = NO;
        self.leftView.hidden = YES;
    }else if (self.mainView.frame.origin.x >0) {
        //显示左边，隐藏右边
        self.leftView.hidden = NO;
        self.rightView.hidden = YES;
    }
}

- (void)addchildview {

    //left
    UIView *leftView = [[UIView alloc]initWithFrame:self.view.bounds];
    leftView.backgroundColor = [UIColor greenColor];
    [self.view addSubview:leftView];
    _leftView = leftView;
    
    //right
    UIView *rightView = [[UIView alloc]initWithFrame:self.view.bounds];
    rightView.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:rightView];
    self.rightView = rightView;
    
    //main
    UIView *mainView = [[UIView alloc]initWithFrame:self.view.bounds];
    mainView.backgroundColor = [UIColor redColor];
    [self.view addSubview:mainView];
    self.mainView = mainView;
    
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    //获取手指
    UITouch *touch = [touches anyObject];
    
    //当前点
    CGPoint curP = [touch locationInView:self.view];
    //上一个点
    CGPoint preP = [touch previousLocationInView:self.view];
    
    //获取手指每移动一下，x轴的偏移量
    CGFloat offsetX = curP.x - preP.x;
    
    //设置当前视图的frame
    self.mainView.frame = [self frameWithOffsetX:offsetX];
    
    //记录下当前正在拖拽
    self.isDraging = YES;
}

# pragma mark - y反向最大的偏移量
#define MaxY 60

- (CGRect)frameWithOffsetX:(CGFloat)offsetX {
    
    CGFloat screenW = [UIScreen mainScreen].bounds.size.width;
    CGFloat screenH = [UIScreen mainScreen].bounds.size.height;
    CGFloat offsetY = offsetX * MaxY / screenW;
    
    //获取缩放比例
    CGFloat scale = (screenH - 2 * offsetY) / screenH;
    
    //右边移动的时候的缩放比例
    if (self.mainView.frame.origin.x < 0) {
        scale = (screenH + 2 * offsetY) / screenH;
    }
    
    CGRect frame = self.mainView.frame;
    frame.origin.x += offsetX;
    frame.size.height = frame.size.height * scale;
    frame.size.width = frame.size.width * scale;
    frame.origin.y = (screenH - frame.size.height) * 0.5;
    
    return frame;
}

#pragma mark - 定位功能
#define targetRX 300
#define TargetLx -250

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    if (_isDraging == NO && _mainView.frame.origin.x != 0) {
        //复位
        [UIView animateWithDuration:0.25 animations:^{
            self.mainView.frame = self.view.bounds;
        }];
        //下面不需要定位
        return;
    }
    
    //定位功能
    CGFloat screenW = [UIScreen mainScreen].bounds.size.width;
    
    //获取当前主视图的frame
    CGRect frame = self.mainView.frame;
    
    CGFloat target = 0;
    
    if (frame.origin.x > screenW * 0.5) {
        //当主视图的x大于屏幕一半，定位到右边
        target = targetRX;
    }else if (CGRectGetMaxX(self.mainView.frame) < screenW * 0.5) {
        //定位左边
        target = TargetLx;
    }
    
    if(target == 0) {
        //还原
        [UIView animateWithDuration:0.25 animations:^{
            self.mainView.frame = self.view.bounds;
        }];
    }else {
    [UIView animateWithDuration:0.25 animations:^{
        //获取x轴偏移量
        CGFloat offsetX = target - frame.origin.x;
        self.mainView.frame = [self frameWithOffsetX:offsetX];
    }];
        
    }
    //记录下当前正在拖拽
    self.isDraging = NO;
    
}


@end