Key Value Observing not allowing Switch statement on enum

Question

I'm trying to use Key Value Observation to detect a change in the torchMode variable for an AVCaptureDevice. I'm having an issue where the switch statement doesn't recognize the value (which is an enum). Any idea whats going on? I know that the program gets to the line with the switch, then immediately skips all the cases. Here's the relevant code:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{

    if (context == CapturingStillImageContext)
    {
        BOOL isCapturingStillImage = [change[NSKeyValueChangeNewKey] boolValue];

        if (isCapturingStillImage)
        {
            [self runStillImageCaptureAnimation];
        }
    }
    else if (context == RecordingContext)
    {
        BOOL isRecording = [change[NSKeyValueChangeNewKey] boolValue];

        dispatch_async(dispatch_get_main_queue(), ^{
            if (isRecording)
            {
                [[self record] setTitle:NSLocalizedString(@"-", @"Recording button stop title") forState:UIControlStateNormal];
                [[self record] setEnabled:YES];
            }
            else
            {
                [[self record] setTitle:NSLocalizedString(@"+", @"Recording button record title") forState:UIControlStateNormal];
                [[self record] setEnabled:YES];
            }
        });
    }
    else if (context == SessionRunningAndDeviceAuthorizedContext)
    {
        BOOL isRunning = [change[NSKeyValueChangeNewKey] boolValue];

        dispatch_async(dispatch_get_main_queue(), ^{
            if (isRunning)
                [[self record] setEnabled:YES];
            else
                [[self record] setEnabled:NO];
        });
    }
    else if (context == TorchContext) {
        id torchValue = [change objectForKey: NSKeyValueChangeNewKey];
        NSString* title;
        switch((AVCaptureTorchMode)torchValue) {
        case AVCaptureTorchModeAuto: title = @"Auto"; break;
        case AVCaptureTorchModeOff: title = @"Off"; break;
        case AVCaptureTorchModeOn: title = @"On"; break;
        }
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.torch setTitle:title forState:UIControlStateNormal];
            //NSLog(self.torch);
        });
    }
    else
    {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

Code for adding observer for key value:

- (void)viewWillAppear:(BOOL)animated
{
    [self.navigationController setNavigationBarHidden:YES animated:NO];
    dispatch_async([self sessionQueue], ^{
        [self addObserver:self forKeyPath:@"sessionRunningAndDeviceAuthorized" options:(NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew) context:SessionRunningAndDeviceAuthorizedContext];
        [self addObserver:self forKeyPath:@"stillImageOutput.capturingStillImage" options:(NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew) context:CapturingStillImageContext];
        [self addObserver:self forKeyPath:@"movieFileOutput.recording" options:(NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew) context:RecordingContext];
        [self addObserver:self forKeyPath:@"videoDeviceInput.device.torchMode" options:(NSKeyValueObservingOptionNew) context:TorchContext];
    ...
}

You are using an object in the switch statement, not an enum. You can't just cast an object to an enum. — Sebastian, Feb 04 '14 at 03:09
Show the code where you add the observer and pass the context. — rmaddy, Feb 04 '14 at 03:13

score 2 · Answer 1 · answered Feb 04 '14 at 03:20

I solved the issue. I'm not sure if this is the most elegant solution, but I just casted the value to an NSNumber and got the integer value, then put it in the switch. Here's the code:

int torchValue = ((NSNumber*)[change objectForKey: NSKeyValueChangeNewKey]).integerValue;
        NSString* title;
        switch(torchValue) {
            case AVCaptureTorchModeAuto: title = @"Auto"; break;
            case AVCaptureTorchModeOff: title = @"Off"; break;
            case AVCaptureTorchModeOn: title = @"On"; break;
        }

Key Value Observing not allowing Switch statement on enum

1 Answers1