UIManagedDocument在后台线程中插入对象

Question

这是我关于Stack Overflow的第一个问题,所以如果我打破任何礼仪,请原谅.我也是Objective-C/app创建的新手.

我一直在关注CS193P斯坦福课程,特别是CoreData讲座/演示.在Paul Hegarty的Photomania应用程序中,他以表格视图开始,并在后台填充数据,而不会中断UI流程.我一直在创建一个列出本地区域业务的应用程序(来自返回JSON数据的api).

我根据Paul的照片/摄影师课程创建了类别.类本身的创建不是问题,而是创建它们的地方.

A simplified data structure:
- Section
    - Sub-section
        - business
        - business
        - business
    - business
    - business
    - business

我的应用程序以带有几个按钮的UIViewController开始,每个按钮打开相应部分的tableview(这些都工作正常,我试图提供足够的信息,以便我的问题有意义).我调用一个帮助方法来创建/打开UIManagedDocument的URL,该URL基于这个问题.一旦应用程序运行,就会调用它,并且它会快速加载.

我有一个非常类似于Paul的fetchFlickrDataIntoDocument的方法:

-(void)refreshBusinessesInDocument:(UIManagedDocument *)document
{
dispatch_queue_t refreshBusinessQ = dispatch_queue_create("Refresh Business Listing", NULL);
dispatch_async(refreshBusinessQ, ^{
    // Get latest business listing
    myFunctions *myFunctions = [[myFunctions alloc] init];
    NSArray *businesses = [myFunctions arrayOfBusinesses];

    // Run IN document's thread
    [document.managedObjectContext performBlock:^{

        // Loop through new businesses and insert
        for (NSDictionary *businessData in businesses) {
            [Business businessWithJSONInfo:businessData inManageObjectContext:document.managedObjectContext];
        }

        // Explicitly save the document.
        [document saveToURL:document.fileURL 
           forSaveOperation:UIDocumentSaveForOverwriting
          completionHandler:^(BOOL success){
              if (!success) {
                  NSLog(@"Document save failed");
              }
          }];
        NSLog(@"Inserted Businesses");
    }];
});
dispatch_release(refreshBusinessQ);
}

[myFunctions arrayOfBusinesses]只解析JSON数据并返回包含各个业务的NSArray.

我已经在业务创建代码的开头和结尾处使用NSLog运行代码.每个企业都分配了一个部分,创建需要0.006秒,其中有几百个.插入物最终耗时约2秒钟.

帮手方法在这里:

// The following typedef has been defined in the .h file
// typedef void (^completion_block_t)(UIManagedDocument *document);

@implementation ManagedDocumentHelper

+(void)openDocument:(NSString *)documentName UsingBlock:(completion_block_t)completionBlock
{
    // Get URL for document -> "<Documents directory>/<documentName>"
    NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
    url = [url URLByAppendingPathComponent:documentName];

    // Attempt retrieval of existing document
    UIManagedDocument *doc = [managedDocumentDictionary objectForKey:documentName];

    // If no UIManagedDocument, create
    if (!doc) 
    {
        // Create with document at URL
        doc = [[UIManagedDocument alloc] initWithFileURL:url];

        // Save in managedDocumentDictionary
        [managedDocumentDictionary setObject:doc forKey:documentName];
    }

    // If the document exists on disk
    if ([[NSFileManager defaultManager] fileExistsAtPath:[url path]]) 
    {
        [doc openWithCompletionHandler:^(BOOL success)
         {
             // Run completion block
             completionBlock(doc);
         } ];
    }
    else
    {
        // Save temporary document to documents directory
        [doc saveToURL:url 
      forSaveOperation:UIDocumentSaveForCreating 
     completionHandler:^(BOOL success)
         {
             // Run compeltion block
             completionBlock(doc);
         }];
    }
}

并在viewDidLoad中调用:

if (!self.lgtbDatabase) {
    [ManagedDocumentHelper openDocument:@"DefaultLGTBDatabase" UsingBlock:^(UIManagedDocument *document){
        [self useDocument:document];
    }];
}

useDocument只是将self.document设置为提供的文档.

我想将此代码更改为以便将数据插入另一个线程中,并且用户仍然可以单击按钮来查看节,而不会导致数据导入挂起UI.

任何帮助将不胜感激我已经在这个问题上工作了几天而无法解决它,即使这里有其他类似的问题.如果您需要任何其他信息,请告诉我们!

谢谢

编辑:

到目前为止,这个问题已经收到一票.如果有办法我可以改进这个问题,或者有人知道我无法找到的问题,请你评论一下如何或在哪里？如果还有其他原因让你失望,请告诉我,因为我无法理解这种消极情绪,并且愿意学习如何做出更好的贡献.

Answer 1

有几种方法可以解决这个问题.

因为你正在使用UIManagedDocument你可以利用NSPrivateQueueConcurrencyType初始化一个新的NSManagedObjectContext和performBlock用来做你的东西.例如:

// create a context with a private queue so access happens on a separate thread.
NSManagedObjectContext *context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
// insert this context into the current context hierarchy
context.parentContext = parentContext;
// execute the block on the queue of the context
context.performBlock:^{

      // do your stuff (e.g. a long import operation)

      // save the context here
      // with parent/child contexts saving a context push the changes out of the current context
      NSError* error = nil;
      [context save:&error];
 }];

从上下文保存时,私有上下文的数据将被推送到当前上下文.保存仅在内存中可见,因此您需要访问主上下文(链接到该主上下文UIDocument)并在那里进行保存(请查看do -a-core-data-parent-managedobjectcontext-need-to-share -a-concurrency-type-wi).

另一种方式(我最喜欢的)是创建一个NSOperation子类并在那里做东西.例如,声明一个NSOperation如下的子类:

//.h
@interface MyOperation : NSOperation

- (id)initWithDocument:(UIManagedDocument*)document;

@end

//.m
@interface MyOperation()

@property (nonatomic, weak) UIManagedDocument *document;

@end

- (id)initWithDocument:(UIManagedDocument*)doc;
{
  if (!(self = [super init])) return nil;

  [self setDocument:doc];

  return self;
}

- (void)main
{ 
  NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init];
  [moc setParentContext:[[self document] managedObjectContext]];

  // do the long stuff here...

  NSError *error = nil;
  [moc save:&error];

  NSManagedObjectContext *mainMOC = [[self document] managedObjectContext];
  [mainMOC performBlock:^{
    NSError *error = nil;
    [mainMOC save:&error];
  }];

  // maybe you want to notify the main thread you have finished to import data, if you post a notification remember to deal with it in the main thread...
}

现在在主线程中,您可以将该操作提供给队列,如下所示:

MyOperation *op = [[MyOperation alloc] initWithDocument:[self document]];
[[self someQueue] addOperation:op];

PS您无法在a的main方法中启动异步操作NSOperation.当main完成后,与运营联代表将不会被调用.要说出真相,但这涉及到处理运行循环或并发行为.

希望有所帮助.