捏合与拖动手势实现视图的缩放拖动 以及 任一边界拖进屏幕自动回弹

实现这个功能也是被逼无奈，项目需要缩放移动有很多小页签的WKWebView，尝试了UIScrollView，但是很不理想，因为webview需要侧滑和上下滑动，所以缩放拖动绝大部分都无法触发，只得采用手势实现。在网上查阅了大量资料，终于实现了该功能，废话不多说，上代码：

1、定义缩放倍数和偏移量

// 缩放倍数
#define minScale  1
#define maxScale  2
// 偏移量
#define Offset 0

2、定义需要用到的属性

@property (nonatomic,strong) UIImageView *imgView;// 要缩放的视图
// 缩放
@property (nonatomic, assign) CGFloat lastScale;// 上一次缩放的比例
@property (nonatomic, strong) UIPinchGestureRecognizer *pinch;// 捏合手势
@property (nonatomic, strong) UIPanGestureRecognizer *pan;// 平移手势

3、初始化视图、手势，并设置手势

    _imgView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"2.jpg"]];
    _imgView.frame = self.view.frame;
    _imgView.userInteractionEnabled = YES;
    [self.view addSubview:_imgView];

    _pinch = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchAction:)];
    _pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panAction:)];

    [_imgView addGestureRecognizer:_pinch];
    [_imgView addGestureRecognizer:_pan];

4、 设置锚点

- (void)adjustAnchorPointForGestureRecognizer:(UIGestureRecognizer *)gestureRecognizer
{
    //UIGestureRecognizerStateBegan意味着手势已经被识别
    if (gestureRecognizer.state ==UIGestureRecognizerStateBegan)
    {
        //手势发生在哪个view上
        UIView *piece = gestureRecognizer.view;
        //获得当前手势在view上的位置。
        CGPoint locationInView = [gestureRecognizer locationInView:piece];

        piece.layer.anchorPoint =CGPointMake(locationInView.x / piece.bounds.size.width, locationInView.y / piece.bounds.size.height);
        //根据在view上的位置设置锚点。
        //防止设置完锚点过后，view的位置发生变化，相当于把view的位置重新定位到原来的位置上。
        CGPoint locationInSuperview = [gestureRecognizer locationInView:piece.superview];
        piece.center = locationInSuperview;
    }
}

5、 缩放方法

- (void)pinchAction:(UIPinchGestureRecognizer *)gestureRecognizer{

    UIGestureRecognizerState state = [gestureRecognizer state];

    if(state == UIGestureRecognizerStateBegan) {
        _lastScale = [gestureRecognizer scale];
    }

    if (gestureRecognizer.scale > 1) {
        [self adjustAnchorPointForGestureRecognizer:gestureRecognizer];
    }else{
        _imgView.layer.anchorPoint =CGPointMake(0.5, 0.5);
        _imgView.center = self.view.center;
    }

    CGFloat currentScale = [[[gestureRecognizer view].layer valueForKeyPath:@"transform.scale"] floatValue];

    if (state == UIGestureRecognizerStateBegan ||
        state == UIGestureRecognizerStateChanged) {

        CGFloat newScale = 1 -  (_lastScale - [gestureRecognizer scale]);
        newScale = MIN(newScale, maxScale / currentScale);
        newScale = MAX(newScale, minScale / currentScale);
        CGAffineTransform transform = CGAffineTransformScale([[gestureRecognizer view] transform], newScale, newScale);
        NSLog(@"newScale = %f,currentScale = %f",newScale,currentScale);
        [gestureRecognizer view].transform = transform;
        _lastScale = [gestureRecognizer scale];
    }
    if (state == UIGestureRecognizerStateEnded) {
        if (currentScale >= minScale && currentScale <= minScale + 0.1) {
            [_imgView removeGestureRecognizer:_pan];
        }else if(currentScale > minScale + 0.1 && currentScale <= maxScale){
            [_imgView addGestureRecognizer:_pan];
        }
    }
}

6、 拖动方法

- (void)panAction:(UIPanGestureRecognizer *)gestureRecognizer{

    if (gestureRecognizer.state == UIGestureRecognizerStateBegan ||
        gestureRecognizer.state == UIGestureRecognizerStateChanged) {

        if (!(_imgView.frame.origin.x == 0 &&
              _imgView.frame.origin.y == 0 &&
              _imgView.frame.size.width == self.view.frame.size.width &&
              _imgView.frame.size.height == self.view.frame.size.height)) {
            CGPoint translation = [gestureRecognizer translationInView:self.view];
            gestureRecognizer.view.center = CGPointMake(gestureRecognizer.view.center.x + translation.x, gestureRecognizer.view.center.y + translation.y);
            [gestureRecognizer setTranslation:CGPointZero inView:self.view];
        }
    }

    CGRect rect = _imgView.frame;
    if (_imgView.frame.origin.x > 0 + Offset) {//左边进入屏幕
        NSLog(@"左边进入屏幕");
        [UIView animateWithDuration:0.25 animations:^{
            CGPoint point = CGPointMake(gestureRecognizer.view.center.x - gestureRecognizer.view.frame.origin.x, gestureRecognizer.view.center.y);
            gestureRecognizer.view.center = point;
        }];
    }else if (CGRectGetMaxX(rect) < self.view.frame.size.width + Offset){
        NSLog(@"右边进入屏幕");
        [UIView animateWithDuration:0.25 animations:^{
            CGRect newRect = CGRectOffset(_imgView.frame, self.view.frame.size.width - CGRectGetMaxX(_imgView.frame), 0);
            _imgView.frame = newRect;

        }];
    }
    if (_imgView.frame.origin.y > 0 + Offset) {//上边进入屏幕
        NSLog(@"上边进入屏幕");
        [UIView animateWithDuration:0.25 animations:^{
            CGPoint point = CGPointMake(gestureRecognizer.view.center.x, gestureRecognizer.view.center.y - gestureRecognizer.view.frame.origin.y);
            gestureRecognizer.view.center = point;
        }];
    }else if(CGRectGetMaxY(rect) < self.view.frame.size.height + Offset){
        NSLog(@"下边进入屏幕");
        [UIView animateWithDuration:0.25 animations:^{
            CGRect newRect = CGRectOffset(_imgView.frame, 0, self.view.frame.size.height - CGRectGetMaxY(_imgView.frame));
            _imgView.frame = newRect;
        }];
    }

}

手势实现也是万不得已才用的，如果有哪位大神解决了UIScrollView缩放有多个侧滑页签，并且可以上下滑动的WKWebView，请给我留言，相互交流，万分感谢。

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