从后台返回时AVCaptureSession失败

Question

我有一个相机预览窗口,90%的时间都运行良好.但是,有时候,如果返回我的应用程序,如果它在后台,则不会显示预览.这是我在视图加载时调用的代码:

- (void) startCamera {

session = [[AVCaptureSession alloc] init];
session.sessionPreset = AVCaptureSessionPresetPhoto;

AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
captureVideoPreviewLayer.frame = _cameraView.bounds;
[_cameraView.layer addSublayer:captureVideoPreviewLayer];
captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
captureVideoPreviewLayer.position=CGPointMake(CGRectGetMidX(_cameraView.bounds), 160);

AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error = nil;

AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
if (!input) {

    NSLog(@"ERROR: %@", error);


    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Important!"
                                                    message:@"Unable to find a camera."
                                                   delegate:nil
                                          cancelButtonTitle:@"Ok"
                                          otherButtonTitles:nil];
    [alert show];
    [alert autorelease];
}

[session addInput:input];

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

[session addOutput:stillImage];
[session startRunning];
}

如果发生这种情况,我可以切换到我的偏好设置视图并再次返回并且al很好,但这是一个我想要杀死的烦人的bug.预览窗口是我的故事板中的UIView.

Answer 1

不要在视图加载时启动捕获会话,而是在viewWillAppear上启动它并在viewWillDissapear上停止它.

看起来你的视图控制器在应用程序处于后台时清理了一些内存.请记住,请确保初始化捕获会话.

懒惰地在私有属性getter方法中分配会话,而不是在start方法中,这样可以避免内存泄漏.