UIImagePickerController Overlay Buttons Not Firing

问题:

I have a UIImagePickerController of type camera when the user lands on a page. I have put a custom camera overlay on top of the UIImagePickerController, but none of the button events are firing. I know most of this code is from a base Apple code, so I am perplexed as to what is happening.

@interface TakePhotoViewController : UIImagePickerController <UIImagePickerControllerDelegate, UINavigationControllerDelegate>
...

- (void)showImagePickerForSourceType:(UIImagePickerControllerSourceType)sourceType
{
if (self.capturedImages.count > 0)
{
    [self.capturedImages removeAllObjects];
}

self.sourceType = sourceType;
self.delegate = self;

if (sourceType == UIImagePickerControllerSourceTypeCamera)
{
    /*
     The user wants to use the camera interface. Set up our custom overlay view for the camera.
     */
    self.showsCameraControls = NO;

    /*
     Load the overlay view from the OverlayView nib file. Self is the File's Owner for the nib file, so the overlayView outlet is set to the main view in the nib. Pass that view to the image picker controller to use as its overlay view, and set self's reference to the view to nil.
     */
    [[NSBundle mainBundle] loadNibNamed:@"CameraOverlay" owner:self options:nil];
    float scale = [self getScaleForFullScreen];
    self.cameraViewTransform = CGAffineTransformMakeScale(scale, scale);
    self.overlayView.frame = self.cameraOverlayView.frame;
    self.cameraOverlayView = self.overlayView;
    self.overlayView = nil;
}

}

The CameraOverlay's owner is TakePhotoViewController. One of the buttons inside of the CameraOverlay sends a Touch Up Inside event to the outlet function listed below. The code in the TakePhotoViewController attached to a button is below, of which no logs are firing:

- (IBAction)outlet:(id)sender {
NSLog(@"outlet");
}

回答1:

The problem is this line:

self.overlayView.frame = self.cameraOverlayView.frame;

Our cameraOverlayView is nil; it has no frame, because it doesn't even exist yet. So we are giving the overlayView a zero frame. It is dimensionless. The button appears, but it has a zero-sized superview and therefore cannot be tapped.

Now, you may ask, why is that? It's because of the way touch delivery works in iOS. To be touchable, a subview's superview must also be touchable, because the superview is hit-tested for the touch before the subview. But a zero-size view is not touchable: your touch misses the overlayView, so it misses the button as well.

The solution might be as simple as giving the overlayView a reasonable real frame. There may also be timing problems about when you do that (e.g. it may be that you cannot really set the frame until the image picker is about to appear - viewWillAppear:), but in any case this is the place to start.