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我有一个iOS应用程序正在从两个线程访问核心数据sql数据库。线程A(主UI线程)更新核心数据记录,然后线程B尝试从线程A刚刚更新的实体集合中读取数据。麻烦的是,线程B不能“看到”线程A持续存在的变化。iOS多线程核心数据应用程序未合并更改
线程B通过将NSOperation子类对象添加到NSOperationQueue来创建。在的NSOperation子类的主要方法如下:
@try {
// register for the moc save notification - this is so that other MOCs can be told to merge the changes
[[NSNotificationCenter defaultCenter]
addObserver:getApp()
selector:@selector(handleDidSaveNotification:)
name:NSManagedObjectContextDidSaveNotification
object:moc];
NSError* error = nil;
if ([moc save:&error] == YES)
{
NSLog(@"%s SAVED FINE",__FUNCTION__);
}else {
NSLog(@"%s NOT saved, error=%@ %@",__FUNCTION__,error,[error localizedDescription]);
}
// unregister from notification
[[NSNotificationCenter defaultCenter]
removeObserver:getApp()
name:NSManagedObjectContextDidSaveNotification
object:moc];
}
@catch (NSException * e) {
NSLog(@"%s Exception: %@",__FUNCTION__, e);
}
主UI的appdelegate包含下面的代码来处理保存通知:
-(void) main {
// NEED to create the MOC here and pass to the methods.
NSManagedObjectContext* moc = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSConfinementConcurrencyType];
[moc setUndoManager:nil];
[moc setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy]; // Had been working for months
[moc setPersistentStoreCoordinator:getApp().persistentStoreCoordinator];
[self doTheWorkWithMOC:moc]; // Actually performs updates, using moc
moc = nil;
}
后来,线程B如下保存它的变化
- (void)handleDidSaveNotification:(NSNotification*) note
{
@try {
// Notifications run on the same thread as the notification caller.
// However, we need to ensure that any db merges run on the main ui thread.
// Hence:
[self performSelectorOnMainThread:@selector(mergeContexts:) withObject:note waitUntilDone:NO];
}
@catch (NSException * e) {
NSLog(@"appDelegate handleDidSaveNotification Exception: %@", e);
}
}
-(void)mergeContexts:(NSNotification*) note
{
if ([__managedObjectContext tryLock]==YES)
{
[__managedObjectContext mergeChangesFromContextDidSaveNotification:note];
[__managedObjectContext unlock];
}
}
大多数时候它都可以正常工作。
但是,我有一个iPad,在线程A读取数据库时,未检测到由线程B写入的更改。
任何人都可以看到我的代码中会导致这种情况的任何东西?
非常感谢
谢谢,我会按照这个建议。 – Journeyman