抽屉效果

• 0.宏

// 宏里面的#，会自动把后面的参数变成C语言的字符串
#define keyPath(objc,keyPath) @(((void)objc.keyPath,#keyPath))


// 获取屏幕的宽度
#define screenW  [UIScreen mainScreen].bounds.size.width

// 宏的操作原理，每输入一个字母就会直接把宏右边的拷贝，并且会自动补齐前面的内容。

#define kTargetR 275

#define kTargetL -250

• 1.添加子控件

- (void)setUpChildView
{
    // left
    UIView *leftV = [[UIView alloc] initWithFrame:self.view.bounds];

    leftV.backgroundColor = [UIColor greenColor];

    [self.view addSubview:leftV];

    _leftV = leftV;

    // right
    UIView *rightV = [[UIView alloc] initWithFrame:self.view.bounds];

    rightV.backgroundColor = [UIColor blueColor];

    [self.view addSubview:rightV];

    _rightV = rightV;

    // main
    UIView *mainV = [[UIView alloc] initWithFrame:self.view.bounds];

    mainV.backgroundColor = [UIColor redColor];

    [self.view addSubview:mainV];

    _mainV = mainV;
}

• 1. 添加拖拽手势

  UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];

    [self.view addGestureRecognizer:pan];

• 3.实现业务逻辑

- (void)pan:(UIPanGestureRecognizer *)pan
{
    // 获取手势的移动的位置
    CGPoint transP = [pan translationInView:self.view];

    // 获取X轴的偏移量
    CGFloat offsetX = transP.x;

    // 修改mainV的Frame
    _mainV.frame = [self frameWithOffsetX:offsetX];

    // 判断下mainV的x是否大于0
    [self observeValueForKeyPath:nil ofObject:nil change:nil context:nil];

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

    // 判断下当手势结束的时候，定位
    if (pan.state == UIGestureRecognizerStateEnded) {
        // 定位


        CGFloat target = 0;
        // 1.判断下main.x > screenW * 0.5,定位到右边 x=275
        if (_mainV.frame.origin.x > screenW * 0.5) {
            // 定位到右边
            target = kTargetR;
        }else if (CGRectGetMaxX(_mainV.frame) < screenW * 0.5){
            // 2.判断下max(main.x) < screenW * 0.5
            target = kTargetL;
        }

        // 获取x轴偏移量
        CGFloat offsetX = target - _mainV.frame.origin.x;


        [UIView animateWithDuration:0.25 animations:^{

            _mainV.frame = target == 0?self.view.bounds:[self frameWithOffsetX:offsetX];
        }];


    }

}

• 4.监听滚动

  • 只要监听的属性一改变，就会调用观察者的这个方法，通知你有新值

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"%@",NSStringFromCGRect(_mainV.frame));

    if (_mainV.frame.origin.x > 0) { // 往右边移动，隐藏蓝色的view
        _rightV.hidden = YES;

    }else if (_mainV.frame.origin.x < 0){ // 往左边移动，显示蓝色的view
        _rightV.hidden = NO;

    }
}

• 5.根据offsetX计算mainV的Frame

- (CGRect)frameWithOffsetX:(CGFloat)offsetX
{
    // 获取上一次的frame
    CGRect frame = _mainV.frame;
    // 获取屏幕的高度
    CGFloat screenH = [UIScreen mainScreen].bounds.size.height;
//    // 获取屏幕的宽度
//    CGFloat screenW = [UIScreen mainScreen].bounds.size.width;

    // X轴每平移一点，Y轴需要移动
    CGFloat offsetY = offsetX * kMaxY / screenW;

    // 获取上一次的高度
    CGFloat preH = frame.size.height;

    // 获取上一次的宽度
    CGFloat preW = frame.size.width;

    // 获取当前的高度
    CGFloat curH = preH - 2 * offsetY;
    if (frame.origin.x < 0) { // 往左移动
        curH = preH + 2 * offsetY;
    }

    // 获取尺寸的缩放比例
    CGFloat scale = curH / preH;

    // 获取当前的宽度
    CGFloat curW = preW * scale;

    // 更改frame

    // 获取当前X
    frame.origin.x += offsetX;

    // 获取当前Y
    CGFloat y = (screenH - curH) / 2;

    frame.origin.y = y;

    frame.size.height = curH;

    frame.size.width = curW;

    return frame;
}