ios - 苹果源代码 - require( error == nil, bail ) 导致错误

Question

我正在尝试使用 Apple 的一些 source code ，但代码中充斥着这些语句:

require( error == nil, bail );

在 ARC 项目中使用时会导致各种错误(“转到 protected 范围”)。

如何解决此代码？

这是一个例子:

- (void)setupAVCapture
{
    NSError *error = nil;

    AVCaptureSession *session = [AVCaptureSession new];
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone)
        [session setSessionPreset:AVCaptureSessionPreset640x480];
    else
        [session setSessionPreset:AVCaptureSessionPresetPhoto];

    // Select a video device, make an input
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput *deviceInput = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];


    require( error == nil, bail ); //ERROR: "Goto into protected scope"

    isUsingFrontFacingCamera = NO;
    if ( [session canAddInput:deviceInput] )
        [session addInput:deviceInput];

    // Make a still image output
    self.stillImageOutput = [AVCaptureStillImageOutput new];
    [self.stillImageOutput addObserver:self forKeyPath:@"capturingStillImage" options:NSKeyValueObservingOptionNew context:(__bridge void *)(AVCaptureStillImageIsCapturingStillImageContext)];
    if ( [session canAddOutput:self.stillImageOutput] )
        [session addOutput:self.stillImageOutput];

    // Make a video data output
    self.videoDataOutput = [AVCaptureVideoDataOutput new];

    // we want BGRA, both CoreGraphics and OpenGL work well with 'BGRA'
    NSDictionary *rgbOutputSettings = [NSDictionary dictionaryWithObject:
                                       [NSNumber numberWithInt:kCMPixelFormat_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
    [self.videoDataOutput setVideoSettings:rgbOutputSettings];
    [self.videoDataOutput setAlwaysDiscardsLateVideoFrames:YES]; // discard if the data output queue is blocked (as we process the still image)

    // create a serial dispatch queue used for the sample buffer delegate as well as when a still image is captured
    // a serial dispatch queue must be used to guarantee that video frames will be delivered in order
    // see the header doc for setSampleBufferDelegate:queue: for more information
    videoDataOutputQueue = dispatch_queue_create("VideoDataOutputQueue", DISPATCH_QUEUE_SERIAL);
    [self.videoDataOutput setSampleBufferDelegate:self queue:videoDataOutputQueue];

    if ( [session canAddOutput:self.videoDataOutput] )
        [session addOutput:self.videoDataOutput];
    [[self.videoDataOutput connectionWithMediaType:AVMediaTypeVideo] setEnabled:NO];

    effectiveScale = 1.0;
    self.previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
    [self.previewLayer setBackgroundColor:[[UIColor blackColor] CGColor]];
    [self.previewLayer setVideoGravity:AVLayerVideoGravityResizeAspect];
    CALayer *rootLayer = [self.previewView layer];
    [rootLayer setMasksToBounds:YES];
    [self.previewLayer setFrame:[rootLayer bounds]];
    [rootLayer addSublayer:self.previewLayer];
    [session startRunning];

bail:
    session = nil;
    if (error) {
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"Failed with error %d", (int)[error code]]
                                                            message:[error localizedDescription]
                                                           delegate:nil
                                                  cancelButtonTitle:@"Dismiss"
                                                  otherButtonTitles:nil];
        [alertView show];
        [self teardownAVCapture];
    }

}

Answer 1

添加左大括号和右大括号以提及范围

require( error == nil, bail );
{

}
bail:
{

}

示例:

require( error == nil, bail );
    {

        isUsingFrontFacingCamera = NO;
        if ( [session canAddInput:deviceInput] )
            [session addInput:deviceInput];

        // Make a still image output
        stillImageOutput = [AVCaptureStillImageOutput new];
        [stillImageOutput addObserver:self forKeyPath:@"capturingStillImage" options:NSKeyValueObservingOptionNew context:(__bridge void *)(AVCaptureStillImageIsCapturingStillImageContext)];
        if ( [session canAddOutput:stillImageOutput] )
            [session addOutput:stillImageOutput];

        // Make a video data output
        videoDataOutput = [AVCaptureVideoDataOutput new];

        // we want BGRA, both CoreGraphics and OpenGL work well with 'BGRA'
        NSDictionary *rgbOutputSettings = [NSDictionary dictionaryWithObject:
                                           [NSNumber numberWithInt:kCMPixelFormat_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
        [videoDataOutput setVideoSettings:rgbOutputSettings];
        [videoDataOutput setAlwaysDiscardsLateVideoFrames:YES]; // discard if the data output queue is blocked (as we process the still image)

        // create a serial dispatch queue used for the sample buffer delegate as well as when a still image is captured
        // a serial dispatch queue must be used to guarantee that video frames will be delivered in order
        // see the header doc for setSampleBufferDelegate:queue: for more information
        videoDataOutputQueue = dispatch_queue_create("VideoDataOutputQueue", DISPATCH_QUEUE_SERIAL);
        [videoDataOutput setSampleBufferDelegate:self queue:videoDataOutputQueue];

        if ( [session canAddOutput:videoDataOutput] )
            [session addOutput:videoDataOutput];
        [[videoDataOutput connectionWithMediaType:AVMediaTypeVideo] setEnabled:NO];

        effectiveScale = 1.0;
        previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
        [previewLayer setBackgroundColor:[[UIColor blackColor] CGColor]];
        [previewLayer setVideoGravity:AVLayerVideoGravityResizeAspect];
        CALayer *rootLayer = [previewView layer];
        [rootLayer setMasksToBounds:YES];
        [previewLayer setFrame:[rootLayer bounds]];
        [rootLayer addSublayer:previewLayer];
        [session startRunning];
    }

bail:
    {

        if (error) {
            UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"Failed with error %d", (int)[error code]]
                                                                message:[error localizedDescription]
                                                               delegate:nil 
                                                      cancelButtonTitle:@"Dismiss" 
                                                      otherButtonTitles:nil];
            [alertView show];

            [self teardownAVCapture];
        }
    }