UIScrollView 显示第一张图像正常，但后续图像缩放和平移不正确

Posted 2023-03-16

【中文标题】UIScrollView 显示第一张图像正常，但后续图像缩放和平移不正确

【英文标题】：UIScrollView displays first image fine but subsequent images zoom and pan incorrectly

【发布时间】：2013-03-30 11:26:29

【问题描述】：

我的应用程序可以从 Flickr 中提取图像，并且可以在 UIScrollView 中选择并显示它们，并启用缩放和平移。我选择的第一张图像很好，平移和缩放按预期工作。但是，我在第一个图像之后加载的任何图像都无法正常运行。平移是有限的，当我第一次缩放它时，它总是将图像重置到屏幕的左上角，并且再次平移非常有限，但是它确实缩放。方法如下：

-(void)loadImageFromURLandSetupScrollView

[self startToolbarActivityIndicator];
dispatch_queue_t downloadQueue = dispatch_queue_create("flickr downloader", NULL);
dispatch_async(downloadQueue, ^
    UIImage *imageFromFlickr = [UIImage imageWithData:[NSData dataWithContentsOfURL:self.photoURL]];
    dispatch_async(dispatch_get_main_queue(), ^
        self.photo.image = imageFromFlickr;
        self.photo.frame = CGRectMake(0, 0, self.photo.image.size.width, self.photo.image.size.height);
        self.scrollView.contentSize = self.photo.bounds.size;

        //setup the zoom scale to show best possible
        float zoomScaleWidth = self.scrollView.bounds.size.width / self.photo.image.size.width;
        float zoomScaleHeight = self.scrollView.bounds.size.height / self.photo.image.size.height;

        if(zoomScaleHeight < zoomScaleWidth)
            self.scrollView.minimumZoomScale = zoomScaleHeight;
            self.scrollView.zoomScale = zoomScaleWidth;
        
        else
            self.scrollView.minimumZoomScale = zoomScaleWidth; //make sure it can't be zoomed less than longest side at full screen
            self.scrollView.zoomScale = zoomScaleHeight;
        
        self.scrollView.maximumZoomScale = 10;

        //set scroll view background colour
        self.scrollView.backgroundColor = [UIColor blackColor];
        [self stopToolBarActivityMonitor];
    );
);

【参考方案1】：

所以这似乎是由新的自动布局功能引起的，我的解决方法是在故事板中没有 UIImageView，而是在需要时以编程方式将其添加到滚动视图中。

-(UIImageView *)photo

if (!_photo) _photo = [[UIImageView alloc] initWithFrame:CGRectZero];
return _photo;


-(void)loadImageFromURLandSetupScrollView
[self startToolbarActivityIndicator];
dispatch_queue_t downloadQueue = dispatch_queue_create("flickr downloader", NULL);
dispatch_async(downloadQueue, ^
    UIImage *imageFromFlickr = [UIImage imageWithData:[NSData dataWithContentsOfURL:self.photoURL]];
    dispatch_async(dispatch_get_main_queue(), ^
        self.photo.image = imageFromFlickr;

        [self.scrollView addSubview:self.photo];
        // Set the min and max:
        self.scrollView.minimumZoomScale = 0.2;
        self.scrollView.maximumZoomScale = 5.0;
        self.scrollView.delegate = self;

        // Set the content:
        self.scrollView.zoomScale = 1.0; // reset zoomScale for new image
        self.scrollView.contentSize = self.photo.image.size;
        self.photo.frame = CGRectMake(0, 0, self.photo.image.size.width, self.photo.image.size.height);

        //setup the zoom scale to show best possible
        float zoomScaleWidth = self.scrollView.bounds.size.width / self.photo.image.size.width;
        float zoomScaleHeight = self.scrollView.bounds.size.height / self.photo.image.size.height;

        if(zoomScaleHeight < zoomScaleWidth)
            self.scrollView.zoomScale = zoomScaleWidth;
        else
            self.scrollView.zoomScale = zoomScaleHeight;

        //set scroll view background colour
        self.scrollView.backgroundColor = [UIColor blackColor];
        [self stopToolBarActivityMonitor];
    );
);