Question

我是Objective-C的初学者，我正在努力使用在iOS 7.1中运行但在iOS 8中崩溃的代码。

我怎么知道堆栈跟踪的问题在哪里？

为什么代码在旧版本（iOS 7）中运行而在较新版本中无效？

使用NSMutableDictionary或NSArray

的错误是否有问题？

- (NSDictionary*) MPNowPlayingInfoCenterNowPlayingInfo {
    NSMutableDictionary *info;

    if (self.currentPlayable && self.currentPlayable.mediaItemProperties) {
        info = self.currentPlayable.mediaItemProperties.mutableCopy;
    } else {
        info = [NSMutableDictionary dictionaryWithCapacity:10];
    }

    //    Set defaults if missing
    NSArray* metadata = self.player.currentItem.asset.commonMetadata;

    if (!info[MPMediaItemPropertyPlaybackDuration]) {
        float _playbackDuration = self.currentPlayerItem ? CMTimeGetSeconds(self.currentPlayerItem.duration) : 0.0f;
        NSNumber* playbackDuration = @(_playbackDuration);
        info[MPMediaItemPropertyPlaybackDuration] = playbackDuration;
    }

    if (!info[MPNowPlayingInfoPropertyElapsedPlaybackTime]) {
        float _elapsedPlaybackTime = self.currentPlayerItem ? CMTimeGetSeconds(self.currentPlayerItem.currentTime) : 0.0f;
        NSNumber* elapsedPlaybackTime = @(_elapsedPlaybackTime);
        info[MPNowPlayingInfoPropertyElapsedPlaybackTime] = elapsedPlaybackTime;
    }

    if (!info[MPMediaItemPropertyArtwork]) {
        NSArray* artworkMetadata = [AVMetadataItem metadataItemsFromArray:metadata
                                                                  withKey:AVMetadataCommonKeyArtwork
                                                                 keySpace:AVMetadataKeySpaceCommon];
        if (artworkMetadata.count > 0) {
            AVMetadataItem* artworkMetadataItem = artworkMetadata[0];

            UIImage* artworkImage = [UIImage imageWithData:artworkMetadataItem.value[@"data"]];
            MPMediaItemArtwork* artwork = [[MPMediaItemArtwork alloc] initWithImage:artworkImage];

            info[MPMediaItemPropertyArtwork] = artwork;
        }
    }

    if (!info[MPMediaItemPropertyTitle]) {
        NSArray* _metadata = [AVMetadataItem metadataItemsFromArray:metadata withKey:AVMetadataCommonKeyTitle keySpace:AVMetadataKeySpaceCommon];

        if (_metadata.count > 0) {
            AVMetadataItem* _metadataItem = _metadata[0];
            info[MPMediaItemPropertyTitle] = _metadataItem.value;
        }
    }

    if (!info[MPMediaItemPropertyAlbumTitle]) {
        NSArray* _metadata = [AVMetadataItem metadataItemsFromArray:metadata withKey:AVMetadataCommonKeyAlbumName keySpace:AVMetadataKeySpaceCommon];

        if (_metadata.count > 0) {
            AVMetadataItem* _metadataItem = _metadata[0];
            info[MPMediaItemPropertyAlbumTitle] = _metadataItem.value;
        }
    }

    if (!info[MPMediaItemPropertyArtist]) {
        NSArray* _metadata = [AVMetadataItem metadataItemsFromArray:metadata withKey:AVMetadataCommonKeyArtist keySpace:AVMetadataKeySpaceCommon];

        if (_metadata.count > 0) {
            AVMetadataItem* _metadataItem = _metadata[0];
            info[MPMediaItemPropertyArtist] = _metadataItem.value;
        }
    }

    return info; 
}

这里是堆栈跟踪：

HelloCordova[20791:74393] THREAD WARNING: ['AudioPlayerPlugin'] took '248.958008' ms. Plugin should use a background thread.
2015-04-01 10:16:21.377 HelloCordova[20791:74903] Retrieving lock screen art...
2015-04-01 10:16:29.295 HelloCordova[20791:74903] Initializing lock screen art...
2015-04-01 10:16:29.296 HelloCordova[20791:74903] Creating MPMediaItemArtwork...
2015-04-01 10:16:29.322 HelloCordova[20791:74903] Done retrieving lock screen art.
2015-04-01 10:16:51.439 HelloCordova[20791:74393] -[__NSCFData objectForKeyedSubscript:]: unrecognized selector sent to instance 0x7ffb33e0fe80
Apr  1 10:16:51 Pourias-Mac.local rtcreporting[20791] <Info>: logging starts...
Apr  1 10:16:51 Pourias-Mac.local rtcreporting[20791] <Debug>: setMessageLoggingBlock: called
2015-04-01 10:16:51.618 HelloCordova[20791:74393] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFData objectForKeyedSubscript:]: unrecognized selector sent to instance 0x7ffb33e0fe80'
*** First throw call stack:
(
    0   CoreFoundation                      0x000000010241ea75 __exceptionPreprocess + 165
    1   libobjc.A.dylib                     0x0000000104f96bb7 objc_exception_throw + 45
    2   CoreFoundation                      0x0000000102425d1d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
    3   CoreFoundation                      0x000000010237d9dc ___forwarding___ + 988
    4   CoreFoundation                      0x000000010237d578 _CF_forwarding_prep_0 + 120
    5   HelloCordova                        0x00000001021ce2a8 -[PRXPlayer MPNowPlayingInfoCenterNowPlayingInfo] + 2056
    6   HelloCordova                        0x00000001021d4549 -[NYPRPlayer MPNowPlayingInfoCenterNowPlayingInfo] + 57
    7   HelloCordova                        0x00000001021ce9e5 -[PRXPlayer setMPNowPlayingInfoCenterNowPlayingInfo] + 85
    8   HelloCordova                        0x00000001021d5acb -[NYPRPlayer refreshMetadata] + 43
    9   HelloCordova                        0x00000001021c4e02 -[AudioStreamHandler updateProgress] + 146
    10  HelloCordova                        0x00000001021c576b -[AudioStreamHandler observedPlayerDidObservePeriodicTimeInterval:] + 91
    11  HelloCordova                        0x00000001021cc85e -[PRXPlayer reportPlayerTimeIntervalToObservers] + 670
    12  HelloCordova                        0x00000001021caa4b -[PRXPlayer playerItemDidJumpTime:] + 91
    13  CoreFoundation                      0x00000001023ee7fc __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 12
    14  CoreFoundation                      0x00000001022ee204 _CFXNotificationPost + 2484
    15  AVFoundation                        0x0000000103b4c0b2 __avplayeritem_fpItemNotificationCallback_block_invoke + 7447
    16  libdispatch.dylib                   0x00000001056b8186 _dispatch_call_block_and_release + 12
    17  libdispatch.dylib                   0x00000001056d7614 _dispatch_client_callout + 8
    18  libdispatch.dylib                   0x00000001056bfa1c _dispatch_main_queue_callback_4CF + 1664
    19  CoreFoundation                      0x0000000102386749 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
    20  CoreFoundation                      0x000000010234962b __CFRunLoopRun + 2043
    21  CoreFoundation                      0x0000000102348bc6 CFRunLoopRunSpecific + 470
    22  GraphicsServices                    0x0000000106735a58 GSEventRunModal + 161
    23  UIKit                               0x000000010280e580 UIApplicationMain + 1282
    24  HelloCordova                        0x000000010219a0e7 main + 71
    25  libdyld.dylib                       0x000000010570c145 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)

这个问题的一部分是This question的副本，但作为noob iOS开发者，我甚至不知道从哪里开始问我的问题，对不起重复的问题，但在其他问题中，我得到了自己的问题回答并将其检查为正确答案。

Answer 1

假设您正在使用Xcode，您可以打开异常断点。这将导致应用程序跳转到抛出异常时已断开的行。

enter image description here

Answer 2

问题是你试图获取objectForKey的东西不是字典而是NSData。我这是这一行：

UIImage* artworkImage = [UIImage imageWithData:artworkMetadataItem.value[@"data"]];

也许你可以在那里添加断点并打印artworkMetadataItem.value以查看它是哪种类型。

如果这不是问题，您可以尝试逐步运行代码以查看导致崩溃的语句。

希望这有效！让我知道它是怎么回事

我怎么知道在Xcode Objective-C中引发错误的位置？

2 个答案: