Take a picture on iPhone without showing controls

问题:

Is there a way to take a picture in code on the iPhone without going through the Apple controls? I have seen a bunch of apps that do this, but I'm not sure what API call to use.

回答1:

Yes, there are two ways to do this. One, available in iOS 3.0+ is to use the UIImagePickerController class, setting the showsCameraControls property to NO, and setting the cameraOverlayView property to your own custom controls. Two, available in iOS 4.0+ is to configure an AVCaptureSession, providing it with an AVCaptureDeviceInput using the appropriate camera device, and AVCaptureStillImageOutput. The first approach is much simpler, and works on more iOS version, but the second approach gives you much greater control over photo resolution and file options.

回答2:

EDIT: As suggested in the comments below, I have now explicitly shown how the AVCaptureSession needs to be declared and initialized. It seems that a few were doing the initialization wrong or declaring AVCaptureSession as a local variable in a method. This would not work.

Following code allows to take a picture using AVCaptureSession without user input:

// Get all cameras in the application and find the frontal camera.
AVCaptureDevice *frontalCamera;
NSArray *allCameras = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];

// Find the frontal camera.
for ( int i = 0; i < allCameras.count; i++ ) {
    AVCaptureDevice *camera = [allCameras objectAtIndex:i];

    if ( camera.position == AVCaptureDevicePositionFront ) {
        frontalCamera = camera;
    }
}

// If we did not find the camera then do not take picture.
if ( frontalCamera != nil ) {
    // Start the process of getting a picture.
    session = [[AVCaptureSession alloc] init];

    // Setup instance of input with frontal camera and add to session.
    NSError *error;
    AVCaptureDeviceInput *input =
    [AVCaptureDeviceInput deviceInputWithDevice:frontalCamera error:&error];

    if ( !error && [session canAddInput:input] ) {
        // Add frontal camera to this session.
        [session addInput:input];

        // We need to capture still image.
        AVCaptureStillImageOutput *output = [[AVCaptureStillImageOutput alloc] init];

        // Captured image. settings.
        [output setOutputSettings:
        [[NSDictionary alloc] initWithObjectsAndKeys:AVVideoCodecJPEG,AVVideoCodecKey,nil]];

        if ( [session canAddOutput:output] ) {
            [session addOutput:output];

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

            // Finally take the picture
            if ( videoConnection ) {
                [session startRunning];

                [output captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) {

                    if (imageDataSampleBuffer != NULL) {
                        NSData *imageData = [AVCaptureStillImageOutput 
                                  jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
                        UIImage *photo = [[UIImage alloc] initWithData:imageData];                                                                 
                    }

                }];
            }
        }
    }
}

session variable is of type AVCaptureSession and has been declared in .h file of the class (either as a property or as a private member of the class):

AVCaptureSession *session;

It will then need to be initialized somewhere for instance in the class' init method:

session = [[AVCaptureSession alloc] init]