应用程序在iPad 3上崩溃，但在iPad 2上未崩溃 - 崩溃日志

Question

我有一个应用程序在iPad2上运行良好，但由于iPad 3崩溃而被Apple拒绝。

我已经符号化了崩溃日志并将崩溃范围缩小到下面的方法。

-(void)mergeTwoVideos {
//AVExport (oddly) has a problem with file name already existing - therefore check if file already exists and delete if needed.
NSFileManager *fileManager = [NSFileManager defaultManager];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *writablePath = [documentsDirectory stringByAppendingPathComponent:@"FinishedVideo.mov"];
if([fileManager fileExistsAtPath:writablePath]){ 
    NSLog(@"Problem - file already exists");
    [fileManager removeItemAtPath:writablePath error:NULL];
}
else{ 
    NSLog(@"No Problem - New File");
}
//Instantiate AVMutable Composition.
CMTime nextClipStartTime = kCMTimeZero;
AVURLAsset* a_videoAsset = [AVURLAsset URLAssetWithURL: [assetURLArray objectForKey:kIntroVideo] options:nil];
AVMutableComposition* mixComposition = [AVMutableComposition composition];
CMTimeRange a_timeRange = CMTimeRangeMake(kCMTimeZero,a_videoAsset.duration);
AVMutableCompositionTrack *a_compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableCompositionTrack *compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

[a_compositionVideoTrack insertTimeRange:a_timeRange ofTrack:[[a_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];
nextClipStartTime = CMTimeAdd(nextClipStartTime, a_timeRange.duration);
AVURLAsset* b_videoAsset = [AVURLAsset URLAssetWithURL: [assetURLArray objectForKey:kMainVideo] options:nil];
CMTimeRange b_timeRange = CMTimeRangeMake(kCMTimeZero, b_videoAsset.duration);
[a_compositionVideoTrack insertTimeRange:b_timeRange ofTrack:[[b_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];
[compositionAudioTrack insertTimeRange:b_timeRange ofTrack:[[b_videoAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:nextClipStartTime error:nil];
nextClipStartTime = CMTimeAdd(nextClipStartTime, b_videoAsset.duration);
AVURLAsset* c_videoAsset = [AVURLAsset URLAssetWithURL: [assetURLArray objectForKey:kIntroVideo] options:nil];
CMTimeRange c_timeRange = CMTimeRangeMake(kCMTimeZero, c_videoAsset.duration);
[a_compositionVideoTrack insertTimeRange:c_timeRange ofTrack:[[c_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetMediumQuality];
NSString *exportVideoPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/FinishedVideo.mov"];
NSURL *exportURL = [NSURL fileURLWithPath:exportVideoPath];
exportSession.outputURL = exportURL;
exportSession.shouldOptimizeForNetworkUse = YES;
exportSession.outputFileType = AVFileTypeQuickTimeMovie;
[exportSession exportAsynchronouslyWithCompletionHandler:^{
    switch (exportSession.status) {
        case AVAssetExportSessionStatusFailed:{
            NSLog (@"FAIL");
            break;
        }
        case AVAssetExportSessionStatusCompleted: {
            NSLog (@"SUCCESS");
            [exportSession release];
            [self finishMergingProcess];
}
};
 }];

}

符号化的崩溃日志如下：

Thread 4 name:  Dispatch queue: com.apple.root.default-priority
Thread 4 Crashed:
0   libsystem_kernel.dylib          0x36d4832c __pthread_kill + 8
1   libsystem_c.dylib               0x3173a208 pthread_kill + 48
2   libsystem_c.dylib               0x31733298 abort + 88
3   libc++abi.dylib                 0x36c10f64 abort_message + 40
4   libc++abi.dylib                 0x36c0e346 _ZL17default_terminatev + 18
5   libobjc.A.dylib                 0x3682b350 _objc_terminate + 140
6   libc++abi.dylib                 0x36c0e3be _ZL19safe_handler_callerPFvvE + 70
7   libc++abi.dylib                 0x36c0e44a std::terminate() + 14
8   libc++abi.dylib                 0x36c0f798 __cxa_throw + 116
9   libobjc.A.dylib                 0x3682b290 objc_exception_throw + 88
10  CoreFoundation                  0x31f1f9d4 -[__NSArrayM objectAtIndex:] + 264
11  AppName                         0x00023d6e -[ViewController mergeTwoVideos]     (ViewController.m:746)
12  libdispatch.dylib               0x31eb4c52 _dispatch_call_block_and_release + 6
13  libdispatch.dylib               0x31eb7810 _dispatch_worker_thread2 + 252
14  libsystem_c.dylib               0x316f5df4 _pthread_wqthread + 288
15  libsystem_c.dylib               0x316f5cc8 start_wqthread + 0

任何人都可以提供任何关于导致iPad 3崩溃的原因的见解吗？令人沮丧的是，我没有iPad3来测试自己，所以感谢任何帮助。

谢谢！

Answer 1

您正在尝试从数组没有该数量的元素的 NSArray 中按索引获取对象。

鉴于您有 # 个调用objectAtIndex:0，您没有首先检查数组是空还是 nil，其中任何一个都可能是问题所在。

考虑到代码中没有验证以确保 URL 正确、正在加载资产或预期的位和片段的资产，该代码中存在数十个潜在的故障点。

您需要修改代码以始终保持防御性; 检查 nil，检查空数组，检查加载 URL 失败等...