UIImagePickerController 在缩放时显示黑条 - 这是 iOS 中的错误吗？

Question

编辑：有人建议这篇文章是duplicate，但事实并非如此，因为黑条最初不存在，仿射变换不能解决问题。

我在 iPad Air 2 上运行它并针对 iOS 8。 我有一个UIImagePickerController，其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）：

会出现一个黑条，可以通过将设备方向更改为纵向（这也会显示黑条）然后将其改回来来消除它。

改成纵向后：

返回横向（+放大）：

奇怪的是，在返回横向后，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，直到变为横向时，会出现一个黑条，当返回纵向时，它会保持不变。

将showsCameraControls 设置为YES 时不会发生这种情况。 我怎样才能摆脱这个问题？

更新：Apple 声称已在 iOS 9 中修复此问题。

Answer 1

我找到了一种方法来解决由于缺乏更好的理解而标记错误的方法（苹果提供的示例也会发生这种情况）。

我的解决方案是手动缩放，将UIPinchGestureRecognizer 添加到覆盖视图中。然后控制器必须实现一个缩放回调，这将消除上述现象。

@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