Objective-C：从 UIScrollView 获取缩放的裁剪图像

Posted 2023-02-25

【中文标题】Objective-C：从 UIScrollView 获取缩放的裁剪图像

【英文标题】：Objective-C: Get Scaled Cropped Image from UIScrollView

【发布时间】：2015-10-22 19:59:36

【问题描述】：

场景

我正在开发一个照片共享应用程序。该应用程序需要允许用户在将图像发送到服务器之前裁剪图像。我正在使用 UIScrollView 和 UIImageView 子视图，其中包含我希望用户裁剪的图像。

我的尝试

我曾尝试通过 *** 上的一些解决方案来做到这一点，但它们涉及在用户缩放后截取 UIScrollView 帧的屏幕截图。这不起作用的原因是，当用户在 iPhone 5（320x320，屏幕宽度的完美正方形）上截屏时，当该照片上传并显示在 iPhone 6 Plus（更大的屏幕尺寸）上时，图像将被像素化。

问题

如何在UIScrollView 内获得可能缩放为 3000x3000 的图像并提取与UIScrollView 框架 (320x320) 尺寸相同的图像 但 缩放为 640x640 不会丢失图像分辨率？

插图

【参考方案1】：

首先，你可以继承UIScrollView，里面包含一个UIImageView，初始化这个UIScrollView和UIImageView，分配一个图像实例给UIImageView，这样它就可以显示了。

- (instancetype)initWithFrame:(CGRect)frame
    self = [super initWithFrame:frame];
    if (self) 
        self.delegate = self;
        self.maximumZoomScale = 4.0f;
        self.showsHorizontalScrollIndicator = NO;
        self.showsVerticalScrollIndicator = NO;
        [self loadImageView:frame];
    
    return self;


- (void) loadImageView:(CGRect) frame 
    if (!_imageView) 
        _imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0,(frame.size.height-frame.size.width)/2, frame.size.width, frame.size.width)];
        _imageView.contentMode = UIViewContentModeScaleAspectFit;
        _imageView.center = self.center;
        [self addSubview:_imageView];
    


//call this menthod to assginment image to imageView
- (void)showImage:(UIImage*)image
    self.imageView.image = image;
    [self handleImageType];

其次，可以在viewForZoomingInScrollView和scrollViewDidZoom中处理，代码如下：

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView 

    return _imageView;//your imageView inside UIScrollView
  


- (void)scrollViewDidZoom:(UIScrollView *)scrollView

    CGSize boundSize = self.bounds.size;//scrollView bounds
    CGFloat boundWidth = boundSize.width;
    CGFloat boundHeight = boundSize.height;

    CGSize imageSize = self.imageView.image.size;
    CGFloat imageWidth = imageSize.width;
    CGFloat imageHeight = imageSize.height;

    CGFloat zoomScale = scrollView.zoomScale;
    DLog(@"zoomScale === %f",zoomScale);

    [self normalScaleViewDidZoom:boundWidth boundHeight:boundHeight imageWidth:imageWidth imageHeight:imageHeight scrollView:scrollView];
  

- (void)handleImageType

    CGSize imageSize = self.imageView.image.size;//imageView's image size
    CGFloat imageWidth = imageSize.width;
    CGFloat imageHeight = imageSize.height;
    if (imageWidth > imageHeight) 
      type = 1;
     else if (imageWidth < imageHeight)
      type = 2;
     else if (imageWidth == imageHeight) 
      type = 3;
    

- (void)normalScaleViewDidZoom:(CGFloat)boundWidth boundHeight:(CGFloat)boundHeight imageWidth:(CGFloat)imageWidth imageHeight:(CGFloat)imageHeight scrollView:(UIScrollView*)scrollView

    CGFloat zoomScale = scrollView.zoomScale;
    if (type == 1) 

        self.contentSize = CGSizeMake(boundWidth/imageHeight*imageWidth*zoomScale,boundWidth*zoomScale + (boundHeight-boundWidth));
     else if (type == 2)

        self.contentSize = CGSizeMake(boundWidth*zoomScale,boundWidth/imageWidth*imageHeight*zoomScale + (boundHeight-boundWidth) );
     else if (type == 3) 

        self.contentSize = CGSizeMake(boundWidth*zoomScale,boundHeight-boundWidth+boundWidth*zoomScale);
    
    [self zoomCenter:scrollView];



- (void)zoomCenter:(UIScrollView*)scrollView
    CGFloat offsetX = (scrollView.bounds.size.width > scrollView.contentSize.width)?(scrollView.bounds.size.width - scrollView.contentSize.width)/2 : 0.0;
    CGFloat offsetY = (scrollView.bounds.size.height > scrollView.contentSize.height)?(scrollView.bounds.size.height - scrollView.contentSize.height)/2 : 0.0;
    self.imageView.center = CGPointMake(scrollView.contentSize.width/2 + offsetX,scrollView.contentSize.height/2 + offsetY);

以上所有代码都是我在我的项目中应用的，希望你可以使用：）