ios - 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，因为黑条最初并不存在，仿射变换无法解决该问题。

我在 iPad Air 2 上运行此程序并针对 iOS 8。我有一个 UIImagePickerController，其 showsCameraControls 属性设置为 NO。当横向启动应用程序然后放大时，会发生以下情况(所有图像均未裁剪):

出现黑条，可以通过将设备方向更改为纵向(也将显示黑条)然后再将其改回来消除黑条。

更改为纵向后:

返回横向(+放大):

奇怪的是，返回横向后，缩放 slider 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，返回纵向时该黑条会保留。

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？

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我因缺乏更好的理解而标记为错误的问题(苹果提供的样本也会发生这种情况)。

我的解决方案是通过向叠加 View 添加 UIPinchGestureRecognizer 来进行手动缩放。然后 Controller 必须实现缩放回调，以消除上述现象。

@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