UIImagePickerController 编辑图片时的左下

在 iOS 11 下，如果给 UIImagePickerController 设置 allowsEditing = YES，然后在编辑图片的时候，却发现左下角的那个 取消 按键怎么也没法点击到

解决方法：
只需在使用 UIImagePickerController 的delegate方法中添加一下代码即可

- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
    if ([UIDevice currentDevice].systemVersion.floatValue < 11) {
        return;
    }
    if ([viewController isKindOfClass:NSClassFromString(@"PUPhotoPickerHostViewController")]) {
        [viewController.view.subviews enumerateObjectsUsingBlock:^(__kindof UIView * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
            if (obj.frame.size.width < 42) {
                [viewController.view sendSubviewToBack:obj];
                *stop = YES;
            }
        }];
    }
}

转自：https://stackoverflow.com/questions/46762200/ios-11-uiimagepickercontroller-after-selection-cancel-button-bug