iOS 点击放大图片

这是封装的一个UITapGestureRecognizer，这里记录一下

主要思路

点击图片的时候，首先在window的keywindow上面再创建一个view，然后把图片等比例放大，放到上面，然后操作捏合，移动

UIWindow * window = [UIApplication sharedApplication].keyWindow;
    backView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, windowWidth, windowHeight)];
    backView.backgroundColor = [UIColor blackColor];
    backView.alpha = 0;
    [window addSubview:backView];
    
    UITapGestureRecognizer * tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(hideBackView)];
    [backView addGestureRecognizer:tap];
    
    UIImageView * backImageView = (UIImageView *)self.view;
    oldRect = backImageView.frame;
    
    UIImageView * showImageView = [[UIImageView alloc]initWithFrame:[self.view convertRect:self.view.bounds toView:window]];
    showImageView.image = backImageView.image;
    showImageView.tag = 190231;
    showImageView.userInteractionEnabled = YES;
    [backView addSubview:showImageView];
    
    //缩放手势
    UIPinchGestureRecognizer * pinch = [[UIPinchGestureRecognizer alloc]initWithTarget:self action:@selector(pinchAction:)];
    [showImageView addGestureRecognizer:pinch];
    
    //移动手势
    UIPanGestureRecognizer * pan = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(panAction:)];
    [showImageView addGestureRecognizer:pan];
//放大图片的主要代码
    [UIView animateWithDuration:0.3 animations:^{
      showImageView.frame = CGRectMake(0,(windowHeight - backImageView.image.size.height * windowWidth / backImageView.image.size.width) / 2, windowWidth, backImageView.image.size.height * windowWidth / backImageView.image.size.width);
        backView.alpha = 1;
        newRect = showImageView.frame;
    }];

下面是手势完成的主要操作

缩放手势这里关键是找到放大的比例,首先要理清楚要放大的倍数是多少，如果直接使用sender.scale 这样就是在前一次放大的基础上，再次放大那么多倍，而我们实际要的效果是在前一次放大的基础上，再放大移动的数值，所以每次手指移动放大的倍数应该是上次的sender.scale值减去当前的sender.scale

    UIImageView * showImageView = (UIImageView *)[backView viewWithTag:190231];
   if (sender.state == UIGestureRecognizerStateBegan) {
       pinchChangeValue = 1;
       return;
   }
   CGFloat change = 1 - (pinchChangeValue - sender.scale);
   showImageView.transform = CGAffineTransformScale(showImageView.transform, change, change);
   //记录当前比例
   pinchChangeValue = sender.scale;

移动手势

   //这里和缩放差不多相同的原理
    if (sender.state == UIGestureRecognizerStateBegan) {
        panChangeValueOld = sender.view.center;
        return;
    }
    if (sender.state == UIGestureRecognizerStateChanged) {
        CGPoint translation = [sender translationInView:self.view];
        float newY = panChangeValueOld.y + translation.y;
        float newX = panChangeValueOld.x + translation.x;
        sender.view.center = CGPointMake(newX, newY);
    }

最后是点击收起图片：
这里要处理两次的隐藏，点击的时候判断图片是否被放大了，如果被缩放手势放大的话，先变为点击放大后的尺寸，再变为原先尺寸，如果没有被缩放手势放大，则直接变为原来尺寸

    UIImageView * showImageView = (UIImageView *)[backView viewWithTag:190231];
    if (showImageView.frame.size.width > newRect.size.width) {
        [UIView animateWithDuration:0.3 animations:^{
            showImageView.frame = newRect;
        }];
    }else{
        [UIView animateWithDuration:0.3 animations:^{
            showImageView.frame = oldRect;
            backView.alpha = 0;
        } completion:^(BOOL finished) {
            [backView removeFromSuperview];
        }];
    }

本次练习的demo的地址：demo