问我的相机覆盖iOS 7有什么问题？

EN

@implementation CameraOverlay

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.opaque = NO;
        self.backgroundColor = [UIColor clearColor];

        // load an image to show in the overlay
        UIImage *constraints = [UIImage imageNamed:@"camera_overlay"];
        UIImageView *constraintView = [[UIImageView alloc]initWithImage:constraints];
        constraintView.frame = CGRectMake(30, 100, 260, 200);
        [self addSubview:constraintView];

    }
    return self;
}

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    // Drawing code
}
*/

@end

- (IBAction)scanButton:(UIButton *)sender
{
    CGRect screenRect = [[UIScreen mainScreen]bounds];
    CGFloat screenWidth = screenRect.size.width;
    CGFloat screenHeight = screenRect.size.height;

    CameraOverlay *overlay = [[CameraOverlay alloc]initWithFrame:CGRectMake(0, 0, screenWidth, screenHeight)];

    UIImagePickerController *picker = [[UIImagePickerController alloc]init];
    picker.cameraOverlayView = overlay;
    picker.delegate = self;
    picker.allowsEditing = YES;
    picker.sourceType = UIImagePickerControllerSourceTypeCamera;

    [self presentViewController:picker animated:YES completion:NULL];
}