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

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 Realm, 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 to listen the data changed event from Realm, then update data to UI for you. You will not have to implement Realm notifications by youself for every viewcontroller.

What you need is two classes OwlRealmCVDataSource and OwlRealmCVDelegate. So, copy them to anywhere in your project. Because this library use Realm, so you must have RealmSwift 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 cells to your collection view.
• Prepare datasource for you collection view
• Make your viewcontroller conform UICollectionViewDelegate, UICollectionViewDataSource

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

• Create collection view data source with OwlRealmCVDataSource

    let dataSource = OwlRealmCVDataSource.datasourceConfig(withClass: Owl.self, predicate: NSPredicate.init(value: true), sortBy: "height", sortAscending: true)
    // `Owl` is a Realm object, 'height' is one property of Owl 
  

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

    class OwlDel: OwlRealmCVDelegate {
        weak var vc: ViewController!
  
        class func delegateForCV(grid:UICollectionView,
            withVC vc:ViewController,
            datasource:OwlRealmCVDataSource) -> 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.dataObject(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 Realm, and don't care how UI update. It also update when you a view controller is not displayed to user.

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