当我想通过下载和解析json文件来更新我的Core Data文件时,我的应用程序有时会崩溃.我收到以下错误：
CoreData: error: SerIoUs application error. Exception was caught
during Core Data change processing. This is usually a bug within an
observer of NSManagedobjectContextObjectsDidChangeNotification.
-[__NSCFSet addobject:]: attempt to insert nil with userInfo (null)
如果我在迭代期间更改属性,在迭代中保存NSManagedobjectContext的位置是否重要？
这是我的代码：
- (void) updateData
{
dispatch_queue_t serialdQueue;
serialdQueue = dispatch_queue_create("update",NULL);
dispatch_async(serialdQueue,^{
[self method1];
});
dispatch_async(serialdQueue,^{
[self method2];
});
dispatch_async(serialdQueue,^{
[self method3];
});
dispatch_async(serialdQueue,^{
[self method4];
});
dispatch_async(serialdQueue,^{
[self method5];
});
}
-(void)method1
{
//DOWNLOAD JSON FILE
}
-(void)method2 //here i add objects to the core data file
{
@try {
for (NSDictionary *jsonActivity in [json objectForKey:@"Activities"]) { //IteraTE THROUGH JSON ACTIVITY ARRAY
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Activity" inManagedobjectContext:self.managedobjectContext];
[request setEntity:entity];
nspredicate *searchFilter = [nspredicate predicateWithFormat:@"title == %@",[jsonActivity objectForKey:@"title"]]; // CHECK IF OBJECT FROM JSON FILE ALREADY EXISTS...
[request setPredicate:searchFilter];
NSError *error = nil;
NSArray *results = [self.managedobjectContext executeFetchRequest:request error:&error];
if (error) {
NSLog(@"Error %@",error);
abort();
}
if ([results count] == 0) { // ADD NEW ACTIVITY IF OLD LIST DOESNT CONTAIN IT
Activity *activity = [NSEntityDescription insertNewObjectForEntityForName:@"Activity" inManagedobjectContext:self.managedobjectContext];
activity.title = [jsonActivity objectForKey:@"title"];
activity.remove = [NSNumber numberWithBool:NO]; // REMOVE FLAG = NO BECAUSE NEW OBJECTS AREN'T REMOVED
} else {
Activity *activity = (Activity*) [results objectAtIndex:0];
activity.remove = [NSNumber numberWithBool:NO]; // IF OBJECT ALREADY EXISTS IT SHOULD BE OBTAINED
}
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
[appDelegate saveContext]; // SAVE MO CONTEXT
}
} @catch (NSException *exception) {
NSLog(@"Exception: %@",exception);
}
}
-(void)method3 // DELETE OLD OBJECTS
{
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Activity" inManagedobjectContext:self.managedobjectContext];
[fetchRequest setEntity:entityDescription];
nspredicate *searchFilter = [nspredicate predicateWithFormat:@"remove == %@",[NSNumber numberWithBool:YES]];
[fetchRequest setPredicate:searchFilter];
NSArray *objectsToDelete = [[NSArray alloc] init];
NSError *error = nil;
objectsToDelete = [self.managedobjectContext executeFetchRequest:fetchRequest error:&error];
if (error) {
NSLog(@"Error %@",error);
abort();
}
for (Activity *activity in objectsToDelete) { // DELETE OBJECTS WITH THE PROPERTY REMOVE = YES
[self.managedobjectContext deleteObject:activity]; // DELETE ACTIVITY
}
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
[appDelegate saveContext]; // SAVE MO CONTEXT
}
-(void)method4 // CHANGE THE REMOVE PROPERTY TO YES OF ALL OBJECTS
{
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Activity" inManagedobjectContext:self.managedobjectContext];
[fetchRequest setEntity:entityDescription];
NSArray *objects = [[NSArray alloc] init];
NSError *error = nil;
objects = [self.managedobjectContext executeFetchRequest:fetchRequest error:&error];
if (error) {
NSLog(@"Error %@",error);
abort();
}
for (Activity *activity in objects) {
activity.remove = [NSNumber numberWithBool:YES];
}
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
[appDelegate saveContext]; // SAVE MO CONTEXT
NSLog(@"End Update");
}
-(void)method5 //UPDATE UI
{
//UI UPDATES
}
解决方法
您不应该在serialQueue上访问托管对象上下文.看一下
NSManagedObjectContext documentation的Concurrency部分.
如果在您的代码中您的上下文使用的是nsprivateQueueConcurrencyType或NSMainQueueConcurrencyType并发类型,则可以使用其中一种基于块的方法来确保您处于正确的队列中：
//asyncrhonous
[self.managedobjectContext performBlock:^{
//do stuff with the context
}];
//syncrhonous
[self.managedobjectContext performBlockAndWait:^{
//do stuff with the context
}];