How to use NSCollectionViewItem without subclassing it? - objective-c

Question

I am writing a very simple macOS application that I'd like to show a few images in a collection view. I don't need any special behavior for how they are displayed. The docs for NSCollectionViewItem say:
The default implementation of this class supports the creation of a simple item that displays a single image or string.
That is what I want. However, I can't find any information on how to create a default NSCollectionViewItem.
The documentation for NSCollectionView states:
Every data source object is required to implement the following methods:
collectionView:numberOfItemsInSection:
collectionView:itemForRepresentedObjectAtIndexPath:
The second method above returns an NSCollectionViewItem. From reading examples I gather that the traditional way of creating an NSCollectionViewItem in this case is to call:
NSCollectionViewItem* newCollectionViewItem = [imageCollectionView makeItemWithIdentifier:<some identifier>
forIndexPath:indexPath];
The problem is that I don't understand what <some identifier> should be. I don't have a nib that contains an NSCollectionViewItem because I'm not subclassing it or customizing it in any way. I've tried adding the following to my data source:
- (void)awakeFromNib
{
[imageCollectionView registerClass:[NSCollectionViewItem class]
forItemWithIdentifier:#"Image"];
}
where imageCollectionView is the NSCollectionView in question. And then in my - (NSCollectionViewItem *)collectionView:itemForRepresentedObjectAtIndexPath: method, I call:
NSCollectionViewItem* newCollectionViewItem = [imageCollectionView makeItemWithIdentifier:#"Image"
forIndexPath:indexPath];
But this throws an exception and prints this to the console:
2016-12-19 17:51:27.463 MyApp[28177:3926764] -[NSNib _initWithNibNamed:bundle:options:] could not load the nibName: NSCollectionViewItem in bundle (null).
followed by a stack trace.
So how do I go about creating and using an NSCollectionViewItem that isn't subclassed or modified in any way?

Answer 1

Here is a very simple example which uses a Nib for the item's prototype:
#interface ViewController()
#property (weak) IBOutlet NSCollectionView *collectionView;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
NSNib *theNib = [[NSNib alloc] initWithNibNamed:#"Item" bundle:nil];
[self.collectionView registerNib:theNib forItemWithIdentifier:#"item"];
}
#pragma mark NSCollectionViewDataSource
- (NSInteger)numberOfSectionsInCollectionView:(NSCollectionView *)inCollectionView {
return 1;
}
- (NSInteger)collectionView:(NSCollectionView *)inCollectionView numberOfItemsInSection:(NSInteger)inSection {
return 10;
}
- (NSCollectionViewItem *)collectionView:(NSCollectionView *)inCollectionView itemForRepresentedObjectAtIndexPath:(NSIndexPath *)inIndexPath {
NSCollectionViewItem *theItem = [inCollectionView makeItemWithIdentifier:#"item" forIndexPath:inIndexPath];
NSTextField *theLabel = (NSTextField *)theItem.view;
theLabel.stringValue = [NSString stringWithFormat:#"%d.%d", (int)inIndexPath.section, (int)inIndexPath.item];
return theItem;
}
#end
The NIB contains just a NSCollectionViewItem with a text field as view.
Addendum:
I think you should create a NSCollectionViewItem.xib for the registerClass variant. A view controller will search for a NIB with its class name, if you doesn't create its view manually in loadView. Thus, you can't use plain NSCollectionViewItem without a NIB for registering a class, because of makeItemWithIdentifier:forIndexPath: will access the view of the item.

Answer 2

I found a way to set up NSCollectionView without needing to add a .xib file.
The trick was inheriting from NSCollectionViewItem and using that subclass for -[NSCollectionView registerClass:forItemWithIdentifier:].
#import "ViewController.h"
#interface MyViewItem : NSCollectionViewItem
#end
#implementation MyViewItem {
}
- (instancetype)initWithNibName:(NSNibName)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
self = [super initWithNibName:nil bundle:nil];
NSButton *button = [[NSButton alloc] initWithFrame:NSZeroRect];
[button setTitle:#"Button"];
[self setView:button];
return self;
}
#end
#implementation ViewController {
IBOutlet NSCollectionView *_collectionView;
}
- (void)viewDidLoad {
[super viewDidLoad];
[_collectionView registerClass:[MyViewItem class]
forItemWithIdentifier:#"item"];
[_collectionView setDataSource:self];
}
- (NSInteger)collectionView:(NSCollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return 10;
}
- (NSCollectionViewItem *)collectionView:(NSCollectionView *)collectionView itemForRepresentedObjectAtIndexPath:(NSIndexPath *)indexPath {
return [_collectionView makeItemWithIdentifier:#"item" forIndexPath:indexPath];
}
#end