Question

我只有OS X 10.9，非文档应用程序当我没有在托管对象上下文中明确调用-save:时，Core Data何时自行调用-save:？
到目前为止，我只是发现它在退出应用程序之前已经保存了。

Answer 1

我不认为moc会自行保存

Answer 2

嗯...在iOS中答案很简单。它永远不会。由于NSManagedObjectContext的线程依赖性，我很想说这对OSX来说是相同的。

NSManagedObjectContext保存自己是没有意义的。

如果用户在创建对象的一半时间退出应用并且未完全创建对象，会发生什么？它会在半完成状态下保存吗？

Answer 3

如果你选中了核心数据＆＃34;在创建一个新的Xcode项目时，应该在你的app delegate中找到它：

- (void)applicationWillTerminate:(UIApplication *)application {
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    // Saves changes in the application's managed object context before the application terminates.
    [self saveContext];
}

#pragma mark - Core Data Saving support

- (void)saveContext {
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil) {
        NSError *error = nil;
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
            // Replace this implementation with code to handle the error appropriately.
            // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }
}

因此，当终止应用程序时，它将显式调用save。

正确的答案是：只有在您上面调用save:时才会保存上下文。但是使用xcode模板可以为你设置。

上面的代码适用于iOS，对于Mac OS X，它看起来像

- (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender {
    // Save changes in the application's managed object context before the application terminates.

    if (!_managedObjectContext) {
        return NSTerminateNow;
    }

    if (![[self managedObjectContext] commitEditing]) {
        NSLog(@"%@:%@ unable to commit editing to terminate", [self class], NSStringFromSelector(_cmd));
        return NSTerminateCancel;
    }

    if (![[self managedObjectContext] hasChanges]) {
        return NSTerminateNow;
    }

    NSError *error = nil;
    if (![[self managedObjectContext] save:&error]) {

        // Customize this code block to include application-specific recovery steps.              
        BOOL result = [sender presentError:error];
        if (result) {
            return NSTerminateCancel;
        }

        NSString *question = NSLocalizedString(@"Could not save changes while quitting. Quit anyway?", @"Quit without saves error question message");
        NSString *info = NSLocalizedString(@"Quitting now will lose any changes you have made since the last successful save", @"Quit without saves error question info");
        NSString *quitButton = NSLocalizedString(@"Quit anyway", @"Quit anyway button title");
        NSString *cancelButton = NSLocalizedString(@"Cancel", @"Cancel button title");
        NSAlert *alert = [[NSAlert alloc] init];
        [alert setMessageText:question];
        [alert setInformativeText:info];
        [alert addButtonWithTitle:quitButton];
        [alert addButtonWithTitle:cancelButton];

        NSInteger answer = [alert runModal];

        if (answer == NSAlertFirstButtonReturn) {
            return NSTerminateCancel;
        }
    }

    return NSTerminateNow;
}

也会调用save:方法。

Core Data何时自行保存托管对象上下文？

3 个答案: