Ios 进行奇怪的行为_Ios_Objective C_Core Data_Nsprogress

Ios 进行奇怪的行为

ios objective-c core-data

Ios 进行奇怪的行为,ios,objective-c,core-data,nsprogress,Ios,Objective C,Core Data,Nsprogress,我有一个由几个子任务组成的大任务。我想为这项重大任务添加进度报告。为此，我想使用NSProgress，根据类文档，我可以使用其子-父机制来完成这种子任务进度为了简化它，假设我有一个大任务，它由一个子任务组成（当然在现实生活中会有更多的子任务）。这就是我所做的： #define kFractionCompletedKeyPath @"fractionCompleted" - (void)runBigTask { _progress = [NSProgress progressWi

我有一个由几个子任务组成的大任务。我想为这项重大任务添加进度报告。
为此，我想使用

NSProgress

，根据类文档，我可以使用其子-父机制来完成这种子任务进度

为了简化它，假设我有一个大任务，它由一个子任务组成（当然在现实生活中会有更多的子任务）。这就是我所做的：

#define kFractionCompletedKeyPath @"fractionCompleted"  

- (void)runBigTask {
    _progress = [NSProgress progressWithTotalUnitCount:100]; // 100 is arbitrary 

    [_progress addObserver:self
                forKeyPath:kFractionCompletedKeyPath
                   options:NSKeyValueObservingOptionNew
                   context:NULL];

    [_progress becomeCurrentWithPendingUnitCount:100]; 
    [self subTask];
    [_progress resignCurrent];
} 

- (void)subTask {
    NSManagedObjectContext *parentContext = self.managedObjectContext; // self is AppDelegate in this example
    NSManagedObjectContext *bgContext = [[NSManagedObjectContext alloc]initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    [bgContext setParentContext:parentContext];

    [bgContext performBlockAndWait:^{
        NSInteger totalUnit = 1000;
        NSInteger completedUnits = 0;
        NSProgress *subProgress = [NSProgress progressWithTotalUnitCount:totalUnit];

        for (int i=0; i < totalUnit; i++) {   

            // run some Core Data related code...  

            completedUnits++;
            subProgress.completedUnitCount = completedUnits;
        }
    }];
}      

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if ([keyPath isEqualToString:kFractionCompletedKeyPath]) {
        if ([object isKindOfClass:[NSProgress class]]) {
            NSProgress *progress = (NSProgress *)object;
            NSLog(@"progress… %f", progress.fractionCompleted);
        }
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

如你所见，打印从1.0、0.5和1.0开始，然后是0.66
从这里开始，它表现正常，并像我预期的那样变为1.0

我试图理解为什么会发生这种情况，我注意到如果我从背景上下文中删除父上下文，它就可以正常工作！我从0.0进步到1.0

你知道为什么会这样吗？我怎样才能解决这个问题

我添加了一个非常来演示这个问题（您可以删除setParentContext:call以查看它在没有它的情况下是否工作正常）

似乎在

[NSManagedObjectModel initWithContentsOfURL:

的内部必须有一个NSProgress计数器。在进入

[self subTask]

之前，您将自己设置为接收任何进度指示器的通知（通过将

\u progress

设置为当前并注册self以观察更改）。然后在该例程中调用lazy getter

self.managedObjectContext

，它反过来调用

[NSManagedObjectModel initWithContentsOfURL:

，它显然有一个2个单位的进度计数器。在调用

[NSProgress becomeCurrentWithPendingUnitCount://code>和[NSProgress resignCurrent]
时，似乎需要非常小心。发生这种情况时，堆栈跟踪如下所示：
(lldb) bt
* thread #1: tid = 0x81f2, 0x0000000105bffcda Foundation`-[NSProgress setTotalUnitCount:], queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
  * frame #0: 0x0000000105bffcda Foundation`-[NSProgress setTotalUnitCount:]
    frame #1: 0x0000000105bfeb1b Foundation`+[NSProgress progressWithTotalUnitCount:] + 87
    frame #2: 0x0000000105a31213 Foundation`_NSReadBytesFromFileWithExtendedAttributes + 287
    frame #3: 0x0000000105a3109d Foundation`-[NSData(NSData) initWithContentsOfFile:] + 89
    frame #4: 0x0000000105a30b40 Foundation`+[NSDictionary(NSDictionary) newWithContentsOf:immutable:] + 101
    frame #5: 0x0000000105a5622a Foundation`+[NSDictionary(NSDictionary) dictionaryWithContentsOfFile:] + 45
    frame #6: 0x00000001043c4560 CoreData`-[NSManagedObjectModelBundle initWithPath:] + 224
    frame #7: 0x00000001043c42ed CoreData`-[NSManagedObjectModel initWithContentsOfURL:] + 205
    frame #8: 0x00000001040f723f CDProgress`-[AppDelegate managedObjectModel](self=0x00007fbe48c21f90, _cmd=0x000000010459b37b) + 223 at AppDelegate.m:127
    frame #9: 0x00000001040f7384 CDProgress`-[AppDelegate persistentStoreCoordinator](self=0x00007fbe48c21f90, _cmd=0x000000010459c1cb) + 228 at AppDelegate.m:142
    frame #10: 0x00000001040f708c CDProgress`-[AppDelegate managedObjectContext](self=0x00007fbe48c21f90, _cmd=0x0000000104598f0d) + 92 at AppDelegate.m:111
    frame #11: 0x00000001040f6bdb CDProgress`-[AppDelegate subTask](self=0x00007fbe48c21f90, _cmd=0x00000001040f7997) + 43 at AppDelegate.m:45
    frame #12: 0x00000001040f6b89 CDProgress`-[AppDelegate runTask](self=0x00007fbe48c21f90, _cmd=0x00000001040f7928) + 233 at AppDelegate.m:40
    frame #13: 0x00000001040f6a4b CDProgress`-[AppDelegate application:didFinishLaunchingWithOptions:](self=0x00007fbe48c21f90, _cmd=0x0000000104f5dba9, application=0x00007fbe48f00fb0, launchOptions=0x0000000000000000) + 571 at AppDelegate.m:26
    frame #14: 0x000000010477c5a5 UIKit`-[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 234
    frame #15: 0x000000010477d0ec UIKit`-[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 2463
    frame #16: 0x000000010477fe5c UIKit`-[UIApplication _runWithMainScene:transitionContext:completion:] + 1350
    frame #17: 0x000000010477ed22 UIKit`-[UIApplication workspaceDidEndTransaction:] + 179
    frame #18: 0x00000001088092a3 FrontBoardServices`__31-[FBSSerialQueue performAsync:]_block_invoke + 16
    frame #19: 0x000000010615fabc CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
    frame #20: 0x0000000106155805 CoreFoundation`__CFRunLoopDoBlocks + 341
    frame #21: 0x00000001061555c5 CoreFoundation`__CFRunLoopRun + 2389
    frame #22: 0x0000000106154a06 CoreFoundation`CFRunLoopRunSpecific + 470
    frame #23: 0x000000010477e799 UIKit`-[UIApplication _run] + 413
    frame #24: 0x0000000104781550 UIKit`UIApplicationMain + 1282
    frame #25: 0x00000001040f7793 CDProgress`main(argc=1, argv=0x00007fff5bb09308) + 115 at main.m:16
    frame #26: 0x000000010686f145 libdyld.dylib`start + 1
(lldb) 

这里发生的事情是，当加载模型时，它正在读取plist文件。读取plist文件将调用-[NSData initWithContentsOfFile:
，它正在主线程上调用+[nsprogresswithtotalunitcount:
。作为，这将创建一个NSProgress，它是当前进度的子进程initWithContentsOfFile:
实际上正在执行此操作，并创建您创建的NSProgress
的新子级：
<NSProgress: 0x7f9353596f80> : Parent: 0x0 / Fraction completed: 0.0000 / Completed: 0 of 1  
   <_NSProgressGroup: 0x7f935601a0d0> : Portion of parent: 100 Children: 1
      <NSProgress: 0x7f935600bf50> : Parent: 0x7f9353596f80 / Fraction completed: 0.0000 / Completed: 0 of 0 

NSProgress可能有点难，但有了一些经验，它会变得更容易。我保证 NSProgress的最佳文档在这里：作为旁注，我将把它作为bug归档。最坏的情况是，他们告诉你它按预期工作。
<NSProgress: 0x7f9353596f80> : Parent: 0x0 / Fraction completed: 0.0000 / Completed: 0 of 1  
   <_NSProgressGroup: 0x7f935601a0d0> : Portion of parent: 100 Children: 1
      <NSProgress: 0x7f935600bf50> : Parent: 0x7f9353596f80 / Fraction completed: 0.0000 / Completed: 0 of 0 

- (void)subTask {
    NSProgress  *progress   = [NSProgress progressWithTotalUnitCount:1];
    NSManagedObjectContext *parentContext = self.managedObjectContext;
    NSManagedObjectContext *bgContext = [[NSManagedObjectContext alloc]initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    [bgContext setParentContext:parentContext];

    [progress becomeCurrentWithPendingUnitCount:1];
    [bgContext performBlock:^{

    ... stuff

    [progress resignCurrent];
}