我正在使用AVFoundation api创建相机预览视图,并且在完成后我遇到了清理问题。如何正确清理AVCaptureSession和AVCaptureVideoPreviewLayer
我发现这个问题的最佳答案是在SO thread,谢谢科多。
但是,他没有解决AVCaptureVideoPreviewLayer的重新分配问题,这就是我遇到麻烦的地方。
在我的视图控制器类中我有startCameraCapture方法中的一些初始化代码。听着Codo的回答,我使用dispatch_set_finalizer_f(_captureQueue, capture_cleanup);
来注册一个在队列真正关闭时要调用的回调函数。 我也保持自我,以确保我的对象不会在队列完成调用我的对象之前消失。然后我使用capture_cleanup回调释放自我。
-(void) startCameraCapture {
_camSession = [[AVCaptureSession alloc] init];
if (_previewLayer == nil) {
_previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:_camSession];
}
_previewLayer.frame = self.compView.bgView.frame;
[self.compView.bgView.layer addSublayer:_previewLayer];
// Get the default camera device
AVCaptureDevice* camera = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
// Create a AVCaptureInput with the camera device
NSError *error=nil;
AVCaptureInput* cameraInput = [[AVCaptureDeviceInput alloc] initWithDevice:camera error:&error];
if (cameraInput == nil) {
NSLog(@"Error to create camera capture:%@",error);
}
AVCaptureVideoDataOutput* videoOutput = [[[AVCaptureVideoDataOutput alloc] init] autorelease];
// create a queue to run the capture on
_captureQueue=dispatch_queue_create("captureQueue", NULL);
dispatch_set_context(_captureQueue, self);
dispatch_set_finalizer_f(_captureQueue, capture_cleanup);
// setup our delegate
[videoOutput setSampleBufferDelegate:self queue:_captureQueue];
dispatch_release(_captureQueue);
// retain self as a workouround a queue finalization bug in apples's sdk
// per Stackoverflow answer https://stackoverflow.com/questions/3741121/how-to-properly-release-an-avcapturesession
[self retain];
// configure the pixel format
videoOutput.videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA], (id)kCVPixelBufferPixelFormatTypeKey,
nil];
// and the size of the frames we want
[_camSession setSessionPreset:AVCaptureSessionPresetMedium];
// Add the input and output
[_camSession addInput:cameraInput];
[_camSession addOutput:videoOutput];
[cameraInput release];
// Start the session
[_camSession startRunning];
}
这里capture_cleanup回调:
static void capture_cleanup(void* p)
{
LiveCompViewController* ar = (LiveCompViewController*)p;
[ar release]; // releases capture session if dealloc is called
}
然后我清理代码看起来是这样的:
-(void) stopCameraCapture {
[_camSession stopRunning];
[_camSession release];
_camSession=nil;
// Remove the layer in order to release the camSession
[_previewLayer removeFromSuperlayer];
_previewLayer = nil;
}
我遇到的问题是,从stopCameraCapture的superlayer去除_previewLayer导致以下控制台错误:
"...modifying layer that is being finalized..."
但我需要删除该层,以便它释放并释放,以便它释放_camSession,然后释放dispatch_queue,最后调用我的capture_cleanup回调,最终释放self。
我不明白为什么我得到控制台错误以及如何解决它。为什么当我打电话给[_previewLayer removeFromSuperlayer]
时,如果self.dealloc没有被调用,该图层正在最终确定。
注意:self是viewController,我还没有弹出它,所以它由NavigationContoller保留。