Objective C/Swift Pinch 放大区域

Posted 2023-03-16

【中文标题】Objective C/Swift Pinch 放大区域

【英文标题】：Objecitve C/Swift Pinch to Zoom into area

【发布时间】：2020-12-14 17:59:05

【问题描述】：

我发现很多关于 SO 的问题可以放大，并且我已经能够按照它们实际运行它，但我遇到的问题是它是如何工作的。

当我捏合缩放时，我认为它会放大到我捏合时手指所在的区域。然而，无论我的手指在哪里，当我捏它时，它会放大到恰好是我视图左上角的同一区域。有什么方法可以控制缩放发生的位置吗？

作为参考，我正在实现我的捏合以使用滚动视图进行缩放，如下所示（在 Objective C 中，但答案可以在 Swift 中）：

 _scrollView = [[UIScrollView alloc] init];// scrollview
 _nestedView = [[UIView alloc] init];// top level view within scrollview that contains everything
 _scrolledView = scrolledView;// the view I want to zoom into when pinching - a UIView in this case

// viewDidLoad
 self.scrollView.translatesAutoresizingMaskIntoConstraints = NO;
  self.nestedView.translatesAutoresizingMaskIntoConstraints = NO;
  [self.scrollView addSubview:self.nestedView];
 
  [self.view addSubview:self.scrollView];
  
  self.scrollView.delegate = self;
  self.scrollView.panGestureRecognizer.enabled = YES;// tried with this on an off but doesn't seem to do anything
  self.scrollView.bouncesZoom = NO;
  self.scrollView.minimumZoomScale = 1.0;
  self.scrollView.maximumZoomScale = 3.0;
  self.scrollView.zoomScale = 1.0;

// Delegate
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView 
  return self.scrolledView;


// Constraints
 [NSLayoutConstraint constraintWithItem:self.nestedView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:0.0],
      [NSLayoutConstraint constraintWithItem:self.nestedView attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeading multiplier:1.0 constant:0.0],
      [NSLayoutConstraint constraintWithItem:self.nestedView attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:0.0],
      [NSLayoutConstraint constraintWithItem:self.nestedView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0.0],
                                            
                                            
      [NSLayoutConstraint constraintWithItem:self.scrollView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:0.0],
      [NSLayoutConstraint constraintWithItem:self.scrollView attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeading multiplier:1.0 constant:0.0],
      [NSLayoutConstraint constraintWithItem:self.scrollView attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:0.0],
      [NSLayoutConstraint constraintWithItem:self.scrollView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0.0],


// scrolledView constraints
 [NSLayoutConstraint constraintWithItem:self.scrolledView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:0.0],
    [NSLayoutConstraint constraintWithItem:self.scrolledView attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeading multiplier:1.0 constant:0.0],
    [NSLayoutConstraint constraintWithItem:self.scrolledView attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:0.0],
    [NSLayoutConstraint constraintWithItem:self.scrolledView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0.0],

同样，缩放缩放发生了，但它只是不断放大到我的视图（scrolledView）的左上角，不幸的是，这使得缩放对我的用例完全没有意义。

【问题讨论】：

还需要设置滚动视图的内容偏移量。

@skaak 我什么时候需要设置这个？随着捏手势的完成？我怎么知道将其设置为什么？

等等，从手册中你会得到以下信息。 为了使缩放和平移工作，代理必须同时实现 viewForZoomingInScrollView: 和 scrollViewDidEndZooming:withView:atScale:;此外，最大（maximumZoomScale）和最小（minimumZoomScale）缩放比例必须不同。我之前的评论也不正确。我认为你需要那个额外的方法。

【参考方案1】：

这是基于本教程的一种方法：https://www.raywenderlich.com/5758454-uiscrollview-tutorial-getting-started

@interface ViewController ()

    UIScrollView *scrollView;
    UIImageView *imageView;
    NSLayoutConstraint *imageViewTopConstraint;
    NSLayoutConstraint *imageViewLeadingConstraint;
    NSLayoutConstraint *imageViewTrailingConstraint;
    NSLayoutConstraint *imageViewBottomConstraint;

@end

@implementation ViewController

- (void)viewDidLoad 
    [super viewDidLoad];

    // set name of image asset here
    NSString *imageName = @"myImage";
    
    UIImage *img = [UIImage imageNamed:imageName];
    NSAssert(img, @"Failed to load image!");

    scrollView = [UIScrollView new];
    imageView = [UIImageView new];
    
    scrollView.translatesAutoresizingMaskIntoConstraints = NO;
    imageView.translatesAutoresizingMaskIntoConstraints = NO;
    
    imageView.contentMode = UIViewContentModeScaleToFill;
    
    [scrollView addSubview:imageView];
    [self.view addSubview:scrollView];

    // respect safe area
    UILayoutGuide *g = [self.view safeAreaLayoutGuide];
    UILayoutGuide *cg = scrollView.contentLayoutGuide;
    
    imageViewTopConstraint = [imageView.topAnchor constraintEqualToAnchor:cg.topAnchor];
    imageViewLeadingConstraint = [imageView.leadingAnchor constraintEqualToAnchor:cg.leadingAnchor];
    imageViewTrailingConstraint = [imageView.trailingAnchor constraintEqualToAnchor:cg.trailingAnchor];
    imageViewBottomConstraint = [imageView.bottomAnchor constraintEqualToAnchor:cg.bottomAnchor];

    [NSLayoutConstraint activateConstraints:@[
        
        [scrollView.topAnchor constraintEqualToAnchor:g.topAnchor constant:0.0],
        [scrollView.leadingAnchor constraintEqualToAnchor:g.leadingAnchor constant:0.0],
        [scrollView.trailingAnchor constraintEqualToAnchor:g.trailingAnchor constant:0.0],
        [scrollView.bottomAnchor constraintEqualToAnchor:g.bottomAnchor constant:0.0],

        imageViewTopConstraint,
        imageViewLeadingConstraint,
        imageViewTrailingConstraint,
        imageViewBottomConstraint,
        
    ]];
    
    scrollView.delegate = self;
    
    // this will be updated
    scrollView.minimumZoomScale = 0.1;
    
    // desired max zoom scale
    scrollView.maximumZoomScale = 5.0;
    
    imageView.image = img;
    imageView.frame = CGRectMake(0.0, 0.0, img.size.width, img.size.height);



- (void)viewDidAppear:(BOOL)animated 
    [super viewDidAppear:animated];
    [self updateMinZoomScaleForSize:scrollView.bounds.size];
    [self updateConstraintsForSize:scrollView.bounds.size];


- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView 
    return imageView;


- (void)scrollViewDidZoom:(UIScrollView *)scrollView 
    [self updateConstraintsForSize:scrollView.frame.size];


- (void)centerImage 
    CGFloat yOffset = (scrollView.frame.size.height - imageView.frame.size.height) * 0.5;
    CGFloat xOffset = (scrollView.frame.size.width - imageView.frame.size.width) * 0.5;
    scrollView.contentOffset = CGPointMake(xOffset, yOffset);


- (void)updateMinZoomScaleForSize:(CGSize)size 
    UIImage *img = imageView.image;
    if (!img) 
        return;
    
    
    CGFloat widthScale = size.width / img.size.width;
    CGFloat heightScale = size.height / img.size.height;
    
    CGFloat minScale = MIN(widthScale, heightScale);

    scrollView.minimumZoomScale = minScale;
    scrollView.zoomScale = minScale;


- (void)updateConstraintsForSize:(CGSize)size 
    CGFloat yOffset = MAX(0.0, (size.height - imageView.frame.size.height) * 0.5);
    imageViewTopConstraint.constant = yOffset;
    imageViewBottomConstraint.constant = yOffset;
    
    CGFloat xOffset = MAX(0.0, (size.width - imageView.frame.size.width) * 0.5);
    imageViewLeadingConstraint.constant = xOffset;
    imageViewTrailingConstraint.constant = xOffset;
    
    [self.view layoutIfNeeded];


@end