Question

我正在使用AVCaptureSession使用AVCaptureVideoDataOutput类中的setSampleBufferDelegate方法从相机捕获帧。委托方法如下所示。你可以看到我转换为UIImage并将其放在UIImageView中。我想将每个UIImage保存到磁盘并将URL存储在新的managedObject中，但我不知道如何正确获取managedObjectContext，因为每个调用都使用串行调度队列生成一个新线程。任何人都可以建议使用CoreData和调度队列的解决方案，以便我可以构建存储在磁盘上的图像集合，并对应于托管对象。

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
/*Lock the image buffer*/
CVPixelBufferLockBaseAddress(imageBuffer,0); 
/*Get information about the image*/
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer); 
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
size_t width = CVPixelBufferGetWidth(imageBuffer); 
size_t height = CVPixelBufferGetHeight(imageBuffer);  

/*Create a CGImageRef from the CVImageBufferRef*/
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
CGImageRef newImage = CGBitmapContextCreateImage(newContext); 

    /*We release some components*/
    CGContextRelease(newContext); 
    CGColorSpaceRelease(colorSpace);

/*We display the result on the image view (We need to change the orientation of the image so that the video is displayed correctly).
     Same thing as for the CALayer we are not in the main thread so ...*/
    UIImage *image= [UIImage imageWithCGImage:newImage scale:1.0 orientation:UIImageOrientationRight];

/*We relase the CGImageRef*/
CGImageRelease(newImage);

[self.imageView performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:YES];

/*We unlock the  image buffer*/
CVPixelBufferUnlockBaseAddress(imageBuffer,0);

[pool drain];
}

Answer 1

recommended solution是为每个线程创建一个新的NSManagedObjectContext，每个线程指向一个NSPersistentStoreCoordinator。您可能还想监听NSManagedObjectContextDidSaveNotification，将更改合并到主线程的上下文中（使用恰当命名的mergeChangesFromContextDidSaveNotification:）。

就个人而言，我喜欢在中心位置使用这样的访问器来处理每线程的上下文：

- (NSManagedObjectContext *) managedObjectContext {
    NSManagedObjectContext *context = [[[NSThread currentThread] threadDictionary] objectForKey:@"NSManagedObjectContext"];
    if (context == nil) {
        context = [[[NSManagedObjectContext alloc] init] autorelease];
        [context setPersistentStoreCoordinator:self.persistentStoreCoordinator];
        [[[NSThread currentThread] threadDictionary] setObject:context forKey:@"NSManagedObjectContext"];
    }
    return context;
}

请记住，您无法在线程之间传递NSManagedObject，这比传递上下文更容易。相反，您必须传递NSManagedObjectID（来自对象的objectID属性），然后在目标线程中使用该线程的上下文的objectWithID:方法来获取等效对象。

AVCaptureSession输出样本缓冲区保存到CoreData

1 个答案: