Undo-Redo Idea

gistfile1.m

- (IBAction)createFrame:(id)sender
{
    NSString *frameType = [frameTypeComboBox stringValue];
    id newFrame = (NSManagedObject *)[NSClassFromString(frameType) createEntity];
    [newFrame setValue:frameType forKey:@"frameType"];
    [newFrame setValue:[[sectionObjectController content] valueForKey:@"identifier"] forKey:@"sectionID"];

    [self addObjectToFramesArrayController:newFrame];
}

- (IBAction)deleteFrame:(id)sender
{
    id selectedFrame = [[framesArrayController selectedObjects] lastObject];
    [self removeObjectFromFramesArrayController:selectedFrame];
}


- (void)addObjectToFramesArrayController:(Frame *)f
{
    void (^successBlock)(NSManagedObject *object) = ^(NSManagedObject *object) { 
        // If the remoting fails, the object is deleted, so only add to undo on success
        
        // Register Undo
        NSUndoManager *undo = [self undoManager];
        [[undo prepareWithInvocationTarget:self] removeObjectFromFramesArrayController:f];

        // Only set the action name if we're not undoing.
        // This way, when this method is called during 'Undo Delete Frame', the action item will end up in redo as 'Redo Delete Frame'
        if (![undo isUndoing]) {
            [undo setActionName:@"Add Frame"];
        }
    };

    NSDictionary *action = [NSDictionary dictionaryWithObjectsAndKeys:f, RemoteObject, successBlock, SuccessBlock, nil];        
    [NSApp sendAction:@selector(postObject:) to:nil from:action];
}

- (void)removeObjectFromFramesArrayController:(Frame *)f
{
    void (^successBlock)(NSManagedObject *object) = ^(NSManagedObject *object) { 
        // If the remoting fails, the object is not deleted, so only add to undo on success
        
       // Get JSON for string (could also be a clone)
       NSString *json = [f json];

       NSUndoManager *undo = [self undoManager];
       [[undo prepareWithInvocationTarget:self] createFrameFromJSON:json];

       // Only set the action name if we're not undoing.
       // This way, when this method is called during 'Undo Add Frame', the action item will end up in redo as 'Redo Add Frame'
       if (![undo isUndoing]) {
           [undo setActionName:@"Delete Frame"];
       }
    };

    NSDictionary *action = [NSDictionary dictionaryWithObjectsAndKeys:f, RemoteObject, successBlock, SuccessBlock, nil];        
    [NSApp sendAction:@selector(postObject:) to:nil from:action];
}

- (void)createFrameFromJSON:(NSString *)s
{
    // create frame from JSON
    [self addObjectToFramesArrayController:newFrame];
}

// Also, we could potentially use KVO to handle edits, although I don't know how this works with nested objects
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSUndoManager *undo = [self undoManager];
    id oldValue = [change objectForKey:NSKeyValueChangeOldKey];
    
    // NSNull objects are used to represent nil in a dictionary
    if (oldValue == [NSNull null]) {
        oldValue = nil;
    }
    
    [[undo prepareWithInvocationTarget:self] changeKeyPath:keyPath ofObject:object toValue:oldValue];
    [undo setActionName:@"Edit Frame"];
}