This is a version for CoreData. If you are using Realm, take a look into this version: https://github.com/thanhtanh/OwlRealmCollectionView

Are you tired when you want to make data be synced between viewcontrollers? Such as you want:

• When you add an item, it will be added into list immediately
• When you delete/edit an item from CoreData, it will be deleted/edited in list
• When you change the value of one item, and want to reorder the items in list, it also do that for you, immediately

This library is written based on NSFetchedResultsController, to listen the data changed event from CoreData, then update data to UI for you. You will not have to implement NSFetchedResultsControllerDelegate by youself for every viewcontroller.

What you need is two classes OwlCVDataSource and OwlCVDelegate. So, copy them to anywhere in your project. Because this library use MagicalRecord, so you should have MagicalRecord in your Podfile.

When you want to implement a UICollectionView in your project, you usually do steps like below:

• Add a UICollectionView to your storyboard. Assume that I name it collectionView
• Add a cell to your collection view.
• Prepare datasource data for you collection view
• Make your viewcontroller conform UICollectionViewDelegate, UICollectionViewDataSource

With OwlCollectionView, you just need to change some small things:

• Create collection view data source with OwlCVDataSource

    let dataSource = OwlCVDataSource.datasourceConfig_dataClass(dataModelClass: Owl.self, predicate: NSPredicate.init(value: true), sortBy: "height", sortAscending: true, groupBy: nil)
    // `Owl` is the model for entity in CoreData
  

• Create a subclass of OwlCVDelegate and implement any method of UICollectionViewDelegate and UICollectionViewDataSource as the normal way

    class OwlDel: OwlCVDelegate {
        var vc: ViewController!
  
        class func delegateForCV(grid:UICollectionView,
            withVC vc:ViewController,
            datasource:OwlCVDataSource) -> OwlDel {
            let delegate = OwlDel()
  
            delegate.vc = vc
            delegate.collectionView = grid
  
            grid.delegate = delegate
            grid.dataSource = delegate
  
            delegate.dataSource = datasource
  
            return delegate
        }
  
        override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
            let obj = self.dataObjectFor(item: nil, at: indexPath) as! Owl
  
            ....
            return item
        }
  
        override func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
  
            return CGSize(width: 200, height: 50)
        }
    }
  

• Initial an delegate object for your collection view

    var del: OwlDel! // class variable
    // init with the dataSource we create above
    // `grid` is the collectionview we want to use
    self.del = OwlDel.delegateForCV(grid: self.grid, withVC:self, datasource:dataSource)
  

• Reload collectionview

    self.grid.reloadData()
  

Please take a look on my attached example to more clean what I said above. Screenshot:

Explain the screenshot:

• Requirement: A timer will add an owl after each 2 seconds with random height (the number at the end of each item). If the new owl with the height already existed in the list, it just been updated info (a random color) only. If height = 2, remove that existed owl. All owls in the list will be sorted by height.
• Solve: At you can see the example in project, I just add/update/delete new owl to CoreData, and don't care how UI update. It also update when you a view controller is not displayed to user.

OwlCollectionView is released under the MIT license. See LICENSE for details.