我使用 AvQueuePlayer 在后台播放音频。为了保持 AvQueuePlayer 的播放列表不为空,我使用键值观察来关注 AvQueuePlayer 的 currentItem 以准备加载下一个播放项。有时它工作得很好,但有时它会失败。
这是我收到的崩溃报告:
Date/Time: 2011-12-16 23:43:58.963 +0800
OS Version: iPhone OS 4.3.5 (8L1)
Report Version: 104
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x4f2ecfe8
Crashed Thread: 0
Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0 libobjc.A.dylib 0x32f0aca4 objc_msgSend + 28
1 Foundation 0x3165386c NSKVONotify + 24
2 Foundation 0x31651bb0 -[NSKeyValueObservance observeValueForKeyPath:ofObject:change:context:] + 220
3 Foundation 0x315fa7ea NSKeyValueNotifyObserver + 210
4 Foundation 0x315fa492 NSKeyValueDidChange + 230
5 Foundation 0x315e666a - [NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] + 70
6 AVFoundation 0x33f190f2 -[AVPlayerItem didChangeValueForKey:] + 26
7 AVFoundation 0x33f1ceba __avplayeritem_fpItemNotificationCallback_block_invoke_1 + 2310
8 libdispatch.dylib 0x338da8e0 _dispatch_call_block_and_release + 4
9 libdispatch.dylib 0x338d61ee _dispatch_main_queue_callback_4CF$VARIANT$up + 306
10 CoreFoundation 0x34c1d934 __CFRunLoopRun + 1328
11 CoreFoundation 0x34badebc CFRunLoopRunSpecific + 224
12 CoreFoundation 0x34baddc4 CFRunLoopRunInMode + 52
13 GraphicsServices 0x33e5e418 GSEventRunModal + 108
14 GraphicsServices 0x33e5e4c4 GSEventRun + 56
15 UIKit 0x31272d62 -[UIApplication _run] + 398
16 UIKit 0x31270800 UIApplicationMain + 664
17 WeatherTunes 0x0004b31e main (main.m:17)
18 WeatherTunes 0x0004b2ac start + 32
以下是我如何使用键值观察:
[_queuePlayer addObserver:self forKeyPath:@"currentItem" options:NSKeyValueObservingOptionNew context:nil];
[_queuePlayer addObserver:self forKeyPath:@"currentItem.status" options:NSKeyValueObservingOptionNew context:nil];
我在 AvPlayer 的类参考中查找。然后我发现据说属性“状态”可以观察到,而它没有提到currentItem。但我发现有些人使用属性 currentItem 作为可观察的。我现在完全糊涂了。请帮我。