Iphone 如何停止Arc中的SquareCamController Apple示例演示项目？

在我的应用程序中，我使用苹果公司提供的人脸检测示例代码。该代码是在ARC之前编写的，它有很多非ARC代码。 我将项目转换为Arc，并在我的Arc项目中运行良好。唯一的问题似乎是我可以看到该类中的nslog语句仍在运行，并且应用程序在几分钟后崩溃。如果我把断点放在那个类中，它也会停止，这意味着在视图被取消后，它仍然在后台运行，最终导致崩溃

以下是导致崩溃的代码：

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{   
    // got an image
    CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CFDictionaryRef attachments = CMCopyDictionaryOfAttachments(kCFAllocatorDefault, sampleBuffer, kCMAttachmentMode_ShouldPropagate);
    CIImage *ciImage = [[CIImage alloc] initWithCVPixelBuffer:pixelBuffer options:(__bridge NSDictionary *)attachments];
    if (attachments)
        CFRelease(attachments);
    NSDictionary *imageOptions = nil;
    UIDeviceOrientation curDeviceOrientation = [[UIDevice currentDevice] orientation];
    int exifOrientation;

    /* kCGImagePropertyOrientation values
        The intended display orientation of the image. If present, this key is a CFNumber value with the same value as defined
        by the TIFF and EXIF specifications -- see enumeration of integer constants. 
        The value specified where the origin (0,0) of the image is located. If not present, a value of 1 is assumed.

        used when calling featuresInImage: options: The value for this key is an integer NSNumber from 1..8 as found in kCGImagePropertyOrientation.
        If present, the detection will be done based on that orientation but the coordinates in the returned features will still be based on those of the image. */

    enum {
        PHOTOS_EXIF_0ROW_TOP_0COL_LEFT          = 1, //   1  =  0th row is at the top, and 0th column is on the left (THE DEFAULT).
        PHOTOS_EXIF_0ROW_TOP_0COL_RIGHT         = 2, //   2  =  0th row is at the top, and 0th column is on the right.  
        PHOTOS_EXIF_0ROW_BOTTOM_0COL_RIGHT      = 3, //   3  =  0th row is at the bottom, and 0th column is on the right.  
        PHOTOS_EXIF_0ROW_BOTTOM_0COL_LEFT       = 4, //   4  =  0th row is at the bottom, and 0th column is on the left.  
        PHOTOS_EXIF_0ROW_LEFT_0COL_TOP          = 5, //   5  =  0th row is on the left, and 0th column is the top.  
        PHOTOS_EXIF_0ROW_RIGHT_0COL_TOP         = 6, //   6  =  0th row is on the right, and 0th column is the top.  
        PHOTOS_EXIF_0ROW_RIGHT_0COL_BOTTOM      = 7, //   7  =  0th row is on the right, and 0th column is the bottom.  
        PHOTOS_EXIF_0ROW_LEFT_0COL_BOTTOM       = 8  //   8  =  0th row is on the left, and 0th column is the bottom.  
    };

    switch (curDeviceOrientation) {
        case UIDeviceOrientationPortraitUpsideDown:  // Device oriented vertically, home button on the top
            exifOrientation = PHOTOS_EXIF_0ROW_LEFT_0COL_BOTTOM;
            break;
        case UIDeviceOrientationLandscapeLeft:       // Device oriented horizontally, home button on the right
            if (isUsingFrontFacingCamera)
                exifOrientation = PHOTOS_EXIF_0ROW_BOTTOM_0COL_RIGHT;
            else
                exifOrientation = PHOTOS_EXIF_0ROW_TOP_0COL_LEFT;
            break;
        case UIDeviceOrientationLandscapeRight:      // Device oriented horizontally, home button on the left
            if (isUsingFrontFacingCamera)
                exifOrientation = PHOTOS_EXIF_0ROW_TOP_0COL_LEFT;
            else
                exifOrientation = PHOTOS_EXIF_0ROW_BOTTOM_0COL_RIGHT;
            break;
        case UIDeviceOrientationPortrait:            // Device oriented vertically, home button on the bottom
        default:
            exifOrientation = PHOTOS_EXIF_0ROW_RIGHT_0COL_TOP;
            break;
    }

    imageOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:exifOrientation] forKey:CIDetectorImageOrientation];
    NSArray *features = [faceDetector featuresInImage:ciImage options:imageOptions];

    // get the clean aperture
    // the clean aperture is a rectangle that defines the portion of the encoded pixel dimensions
    // that represents image data valid for display.
    CMFormatDescriptionRef fdesc = CMSampleBufferGetFormatDescription(sampleBuffer);
    CGRect clap = CMVideoFormatDescriptionGetCleanAperture(fdesc, false /*originIsTopLeft == false*/);

    dispatch_async(dispatch_get_main_queue(), ^(void) {
        [self drawFaceBoxesForFeatures:features forVideoBox:clap orientation:curDeviceOrientation]; --------->>>>>> Its crashing here
    });
}