Cocoa NSOutlineView deselect previous selection

I have a NSOutlineView, some of those have children some don't. I would like to deselect, or close the previous selection when a selection is made on other cell.

I hope I can be explanatory with these screen shots.

Here we have Two Parent Folders, Folder 1 and Folder 2. I want to deselect Folder 1 on selecting the disclosure triangle of Folder 2.

Something like this, using the

-(BOOL)outlineView:(NSOutlineView *)outlineView shouldExpandItem:(id)item;
-(BOOL)outlineView:(NSOutlineView *)outlineView shouldCollapseItem:(id)item;

I haven't found a way out.

Thanks

Implement this delegate and use something similar :

- (void)outlineViewItemDidExpand:(NSNotification *)notification{
    for (id parent in list) {
        if ([notification.userInfo objectForKey:@"NSObject"] == parent) {
            continue;
        }
        [notification.object collapseItem:parent];
    }
}

Here parent is the top level item array, as in your example Folder1 and Folder2.

EDIT:

Appdelegate.h

@interface AppDelegate : NSObject <NSApplicationDelegate>

@property (assign) IBOutlet NSWindow *window;

@property(strong) NSDictionary *firstParent;
@property(strong)  NSDictionary *secondParent;
@property(strong) NSArray *list;

@end

Appdelegate.m

@implementation AppDelegate

@synthesize firstParent;
@synthesize secondParent;
@synthesize list;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    // Insert code here to initialize your application
}

- (id)init {
    self = [super init];
    if (self) {

        firstParent = [NSDictionary dictionaryWithObjectsAndKeys:@"A",@"parent",
                       [NSArray arrayWithObjects:@"Apple",@"Aeroplane", nil],@"children", nil];

        secondParent = [NSDictionary dictionaryWithObjectsAndKeys:@"B",@"parent",
                        [NSArray arrayWithObjects:@"Ball",@"Baloon", nil],@"children", nil];
        list = [NSArray arrayWithObjects:firstParent,secondParent, nil];

    }
    return self;
}


- (BOOL)outlineView:(NSOutlineView *)outlineView isItemExpandable:(id)item{
    if ([item isKindOfClass:[NSDictionary class]]) {
        return YES;
    }
    else {
        return NO;
    }
}

- (NSInteger)outlineView:(NSOutlineView *)outlineView numberOfChildrenOfItem:(id)item{

    if (item == nil) { //item is nil when the outline view wants to inquire for root level items
        return [list count];
    }

    if ([item isKindOfClass:[NSDictionary class]]) {
        return [[item objectForKey:@"children"] count];
    }

    return 0;
}

- (id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item{

    if (item == nil) { //item is nil when the outline view wants to inquire for root level items
        return [list objectAtIndex:index];
    }

    if ([item isKindOfClass:[NSDictionary class]]) {
        return [[item objectForKey:@"children"] objectAtIndex:index];
    }

    return nil;
}

- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)theColumn byItem:(id)item
{

    if ([[theColumn identifier] isEqualToString:@"children"]) {
        if ([item isKindOfClass:[NSDictionary class]]) {
            return [NSString stringWithFormat:@"%ld kids",[[item objectForKey:@"children"] count]];
        }
        return item;
    }
    else{
        if ([item isKindOfClass:[NSDictionary class]]) {
            return [item objectForKey:@"parent"];
        }
    }

    return nil;
}

With one more method written on top.

And set the delegate of NSOutlineView to AppDelegate in IB.