使用核心数据保存对现有实体的更改

Question

我有一个笔记应用程序，我试图在Apple Notes应用程序之后进行建模。我有一个NotesTableViewController显示现有的笔记，并有一个按钮来添加新的笔记。当触摸添加新笔记按钮时，NoteViewController被压入堆栈，用户可以键入他们的笔记。当后退按钮被按下时，下面的saveNote方法被调用。这部分工作正常。当我尝试保存对现有笔记的更改时，问题就出现了。我从NotesTableViewController中选择一个笔记，NoteViewController出现，我做了一些更改，并在完成后按下后退按钮。这只是创建一个新的笔记，而不是更新现有的笔记。如何修改下面的方法来完成此操作？

- (void) saveNote 
{ 
    NSLog(@"Save"); 
    NSManagedObjectContext *context = self.managedObjectContext; 

    NSEntityDescription *entity = [NSEntityDescription 
            entityForName:@"Note" 
            inManagedObjectContext:context]; 

    Note *newManagedObject = 
    [NSEntityDescription insertNewObjectForEntityForName:[entity name] 
            inManagedObjectContext:context]; 

    // If appropriate, configure the new managed object. 
    if ([textView hasText]) 
    { 
     [newManagedObject setValue:[NSDate date] forKey:@"timeStamp"]; 
     [newManagedObject setValue:self.title forKey:@"noteName"]; 
     [newManagedObject setValue:textView.text forKey:@"noteText"]; 
     //NSLog(@"%@", textView.text); 
    } 

    NSError *error = nil; 
    if (![context save:&error]) { 
     /* 
     Replace this implementation with code to handle the error 
     appropriately. 

     */ 
     NSLog(@"Unresolved error %@, %@", error, [error userInfo]); 
     abort(); 
    } 

    [self.navigationController popViewControllerAnimated:YES]; 
} 

Answer 1

明白了。以下是可用的新saveNote方法。另外，在NotesTableViewController的tableView：didSelectRowAtIndexPath中：我没有将NoteViewController的managedObject设置为选定的managedObject。

Note *managedNoteObject = [self.fetchedResultsController objectAtIndexPath:indexPath]; 
// Where detailViewController is an instance of NoteViewController. 
detailViewController.managedObject = managedNoteObject; 


- (void) saveNote 
{ 
    NSLog(@"Save"); 

    if([textView hasText]) 
    { 
     [managedObject setValue:[NSDate date] forKey:@"timeStamp"]; 
     NSLog(@"timeStamp: %@", [managedObject valueForKey:@"timeStamp"]); 
     [managedObject setValue:self.title forKey:@"noteName"]; 
     NSLog(@"NoteName: %@", [managedObject valueForKey:@"noteName"]); 
     [managedObject setValue:textView.text forKey:@"noteText"]; 
     NSLog(@"%@", managedObject); 
    } 

    NSError *error = nil; 
    if (![self.managedObjectContext save:&error]) { 
     /* 
     Replace this implementation with code to handle the error 
     appropriately. 

     */ 
     NSLog(@"Unresolved error %@, %@", error, [error userInfo]); 
     abort(); 
    } 
    [self.navigationController popViewControllerAnimated:YES]; 
}