UIImagePickerController 在缩放时显示黑条 – 这是 iOS 中的错误吗? [英] UIImagePickerController shows black bar when zooming – Is this a bug in iOS?

问题描述

编辑:有人建议此帖子是重复，情况并非如此，因为黑条最初不存在，仿射变换不能解决问题.

Edit: It has been suggested this post is a duplicate, which is not the case as the black bars are not initially present an an affine transformation does not remedy the problem.

我在 iPad Air 2 上运行它并针对 iOS 8.我有一个 UIImagePickerController，它的 showsCameraControls 属性设置为 NO.在横向启动应用程序然后放大时，会发生这种情况(所有图像均未裁剪):

I run this on an iPad Air 2 and target iOS 8. I have a UIImagePickerController whose showsCameraControls property is set to NO. When starting the app in landscape and then zooming in, this is what happens (all images are non-cropped):

出现黑条，可以通过将设备方向更改为纵向(也会显示黑条)然后将其改回来来消除.

A black bar appears and can be gotten rid of by changing device orientation to portrait (which will also show the black bar) and then changing it back.

更改为纵向后:

返回横向(+ 放大):

Back to landscape (+ zooming in):

奇怪的是，返回横向后，缩放滑块在缩放过程中不再可见.最初从纵向开始时，首先进行缩放，直到变为横向，此时会出现一个黑条，返回纵向时会保持不变.

Strangely, after returning to landscape, the zoom slider is not visible anymore during zooming. When starting from portrait initially, zooming first works until one changes to landscape, where a black bar appears, which stays when going back to portrait.

当将 showsCameraControls 设置为 YES 时，这些都不会发生.我怎样才能摆脱这个问题?

None of this happens when setting showsCameraControls to YES. How can I get rid of this issue?

更新:Apple 声称已在 iOS 9 中修复此问题.

UPDATE: Apple claims to have fixed this in iOS 9.

推荐答案

我找到了一种方法来解决我缺乏更好理解的问题，我会标记错误(苹果提供的示例也会发生这种情况).

I have found one way to work around what I for lack of better understanding would label a bug (as it happens with apple-provided samples as well).

我的解决方案是手动缩放，方法是将 UIPinchGestureRecognizer 添加到叠加视图.然后控制器必须实现缩放回调，以消除上述现象.

The solution for me is to do manual zooming, by adding a UIPinchGestureRecognizer to the overlay view. The Controller must then implement a zooming callback which will get rid of the phenomenon described above.

@implementation CameraViewController
{
    CGFloat _lastScale; //< the current zoom scale before update
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.imagePicker = [[UIImagePickerController alloc] init];
    self.imagePicker.delegate = self;
    self.imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
    self.imagePicker.allowsEditing = NO;
    self.imagePicker.showsCameraControls = NO;

    [[NSBundle mainBundle] loadNibNamed:@"CameraOverlay" owner:self options:nil];

    UIPinchGestureRecognizer *pinchRec = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(zoom:)];
    [self.overlayView addGestureRecognizer:pinchRec];

    self.imagePicker.cameraOverlayView = self.overlayView;  
    _lastScale = 1.;
}

- (void)zoom:(UIPinchGestureRecognizer *) sender
{
    // reset scale when pinch has ended so that future scalings are applied cumulatively and the zoom does not jump back (not sure I understand this)
    if([sender state] == UIGestureRecognizerStateEnded)
    {
        _lastScale = 1.0;
        return;
    }

    CGFloat scale = 1.0 - (_lastScale - sender.scale); // sender.scale gives current distance of fingers compared to initial distance. We want a value to scale the current transform with, so diff between previous scale and new scale is what must be used to stretch the current transform


    CGAffineTransform currentTransform = self.imagePicker.cameraViewTransform;
    CGAffineTransform newTransform = CGAffineTransformScale (currentTransform, scale, scale); // stretch current transform by amount given by sender

    newTransform.a = MAX(newTransform.a, 1.); // it should be impossible to make preview smaller than screen (or initial size)
    newTransform.d = MAX(newTransform.d, 1.);

    self.imagePicker.cameraViewTransform = newTransform;
    _lastScale = sender.scale;

}
@end

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