使用AVCaptureSession预览捕获图像

Question

我使用AVCaptureSession拍摄快照并保存到相册。拍摄快照后，图像将存储到相册。但我需要在相机预览中显示图像。当我使用UIImagePickerController时，拍照后会显示预览。但是如何处理AVCaptureSession？

代码：

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.



    [self setCaptureSession:[[AVCaptureSession alloc] init]];


    [self  addVideoInputFrontCamera:NO]; // set to YES for Front Camera, No for Back camera

    [self  addStillImageOutput];

    [self setPreviewLayer:[[AVCaptureVideoPreviewLayer alloc] initWithSession:[self captureSession]] ];



    [[self previewLayer] setVideoGravity:AVLayerVideoGravityResizeAspectFill];

    CGRect layerRect = [[[self view] layer] bounds];


    [[self previewLayer]setBounds:layerRect];
    [[self  previewLayer] setPosition:CGPointMake(CGRectGetMidX(layerRect),CGRectGetMidY(layerRect))];
    [[[self view] layer] addSublayer:[self  previewLayer]];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(saveImageToPhotoAlbum) name:kImageCapturedSuccessfully object:nil];


    [[self captureSession] startRunning];
}




- (void)addVideoInputFrontCamera:(BOOL)front {
    NSArray *devices = [AVCaptureDevice devices];
    AVCaptureDevice *frontCamera;
    AVCaptureDevice *backCamera;

    for (AVCaptureDevice *device in devices) {

        NSLog(@"Device name: %@", [device localizedName]);

        if ([device hasMediaType:AVMediaTypeVideo]) {

            if ([device position] == AVCaptureDevicePositionBack) {
                NSLog(@"Device position : back");
                backCamera = device;
            }
            else {
                NSLog(@"Device position : front");
                frontCamera = device;
            }
        }
    }

    NSError *error = nil;

    if (front) {
        AVCaptureDeviceInput *frontFacingCameraDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:frontCamera error:&error];
        if (!error) {
            if ([[self captureSession] canAddInput:frontFacingCameraDeviceInput]) {
                [[self captureSession] addInput:frontFacingCameraDeviceInput];
            } else {
                NSLog(@"Couldn't add front facing video input");
            }
        }
    } else {
        AVCaptureDeviceInput *backFacingCameraDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:backCamera error:&error];
        if (!error) {
            if ([[self captureSession] canAddInput:backFacingCameraDeviceInput]) {
                [[self captureSession] addInput:backFacingCameraDeviceInput];
            } else {
                NSLog(@"Couldn't add back facing video input");
            }
        }
    }
}



- (void)addStillImageOutput
{

    [self setStillImageOutput:[[AVCaptureStillImageOutput alloc] init] ];
        NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys:AVVideoCodecJPEG,AVVideoCodecKey,nil];
        [[self stillImageOutput] setOutputSettings:outputSettings];

        videoConnection = nil;
        for (connection in [[self stillImageOutput] connections]) {
            for (AVCaptureInputPort *port in [connection inputPorts]) {
                if ([[port mediaType] isEqual:AVMediaTypeVideo] ) {
                    videoConnection = connection;
                    break;
                }
            }
            if (videoConnection) {
                break;
            }
        }

        [[self captureSession] addOutput:[self stillImageOutput]];



}



- (void)captureStillImageWithOverlay
{


    videoConnection = nil;
    for (connection in [[self stillImageOutput] connections]) {
        for (AVCaptureInputPort *port in [connection inputPorts]) {
            if ([[port mediaType] isEqual:AVMediaTypeVideo]) {
                videoConnection = connection;
                break;
            }
        }
        if (videoConnection) {
            break;
        }
    }

    NSLog(@"about to request a capture from: %@", [self stillImageOutput]);

    [[self stillImageOutput] captureStillImageAsynchronouslyFromConnection:videoConnection
                                                         completionHandler:^(CMSampleBufferRef imageSampleBuffer, NSError *error) {
                                                             CFDictionaryRef exifAttachments = CMGetAttachment(imageSampleBuffer, kCGImagePropertyExifDictionary, NULL);
                                                             if (exifAttachments) {
                                                                 NSLog(@"attachements: %@", exifAttachments);
                                                             } else {
                                                                 NSLog(@"no attachments");
                                                             }

                                                             NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
                                                             UIImage *image = [[UIImage alloc] initWithData:imageData];

                          [self setStillImage:image];

                                                             //  [image release];
                                                             [[NSNotificationCenter defaultCenter] postNotificationName:kImageCapturedSuccessfully object:nil];

                                                         }];






}


- (void)saveImageToPhotoAlbum
{
     UIImageWriteToSavedPhotosAlbum([self  stillImage], self, @selector(image:didFinishSavingWithError:contextInfo:), nil);

}