我有一个仅限 OS X 10.9 的非文档应用程序。
当我没有在托管对象上下文上显式调用 -save:
时,Core Data 何时自行调用 -save:
?
到目前为止,我只发现它在退出应用程序之前保存。
最佳答案
如果您在创建新的 Xcode 项目时检查了“核心数据”,则应该在您的应用程序委托(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,它将显式调用保存。
正确答案是:只有在调用 save:
时才会保存上下文。但是使用 xcode 模板,这已经为您设置好了。
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;
}
这里也会调用 save:
方法。
关于objective-c - Core Data什么时候自己保存托管对象上下文?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/25410413/