更改子视图后 UIScrollView 不尊重 minimumZoomScale [英] UIScrollView not respecting minimumZoomScale after changing the subview

问题描述

我遇到了一个问题，让 UIScrollView 正确更新以响应最小缩放比例的变化.

I'm hitting a problem getting a UIScrollView to update correctly in response to a change in the minimum zoom scale.

scrollview 有一个 UIImageView 作为子视图，UIImageView 的 image 属性是响应 UIPickerView 的 didFinishPickingMediaWithInfo 方法设置的:

The scrollview has a UIImageView as a subview, and the image property of the UIImageView is set in response to the didFinishPickingMediaWithInfo method of UIPickerView:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {

    UIImage *takenImage = [info objectForKey:UIImagePickerControllerOriginalImage];

    [self.imageView setImage:takenImage];
    [self.imageView setFrame:CGRectMake(self.imageView.frame.origin.x, self.imageView.frame.origin.y, takenImage.size.width, takenImage.size.height)];

    [self.scrollView setContentSize:CGSizeMake(takenImage.size.width, takenImage.size.height)];

    [self.scrollView setMinimumZoomScale:[self.scrollView frame].size.width / takenImage.size.width];
    [self.scrollView setMaximumZoomScale:2.0];
    [self.scrollView setZoomScale:[self.scrollView minimumZoomScale] animated:YES];

    [self dismissModalViewControllerAnimated:YES];        

}

第一次使用此方法添加图像时，这可以正常工作.但是，如果再次触发此方法 - 即使添加与第一次相同的图像 - 后续图像在 scrollView 中以全尺寸显示，并且无法缩小 - 只能放大.

This works correctly the first time an image is added using this method. However, if this method is triggered again - even to add the same image as the first time - the subsequent image is displayed at full size in the scrollView, and can't be zoomed out - only zoomed in.

我已将 scrollView 的 contentSize、zoomScale、minimumZoomScale 和 maximumZoomScale 转储到日志中，他们每次都是一样的.minimumZoomScale 每次都被正确计算.

I've dumped the contentSize, zoomScale, minimumZoomScale and maximumZoomScale of the scrollView to the log, and they are the same each time. The minimumZoomScale is being calculated correctly each time.

就好像使用 1.0 的 minimumZoomScale 重绘 scrollView 一样，忽略了它已显式设置的事实.有什么明显的东西我在这里遗漏了吗?

It's as if the scrollView is being redrawn with a minimumZoomScale of 1.0, ignoring the fact it's been explicitly set. Is there something obvious that I'm missing here?

推荐答案

问题似乎是 - 不确定此行为是否记录在某处 - 在当前缩放比例设置为 1.0 以外的其他值时重置内容大小.

The problem seems to be - not sure if this behavior is documented somewhere - resetting the content size while the current zoom scale is set to something other than 1.0.

修复很简单:在设置新内容大小之前，将 zoomScale 属性重置为 1.0 :

The fix is simple: Reset the zoomScale property to 1.0 before setting the new content size:

// See http://stackoverflow.com/questions/10586577
// first reset before new content size
scroller.zoomScale = 1.0f;
// set new content size
scroller.contentSize = newImage.size;
// ... adjust minimum/maximum zoom scales if needed

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