Fixed tail loading example (#105)

Summary:
- Fixes #105
- ~~Added a 'SpinnerSectionController' allowing us to trigger the activity spinner each time~~
- Changed the words array to be numbers instead (I found it personally difficult to realise if more cells were actually added as the text didn't seem to change, by using numbers you can quite clearly see it increment by 5 each time you load more)
- No changes/new tests as it is a fix to an example

- [x] All tests pass. Demo project builds and runs.
- [x] I added tests, an experiment, or detailed why my change isn't tested.
- [x] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/CONTRIBUTING.md)
Closes #109

Differential Revision: D4066700

Pulled By: rnystrom

fbshipit-source-id: 7779a8ba39361cfa2e782db9460e693e90f1a478

Example/IGListKitExamples/Assets.xcassets/AppIcon.appiconset/Contents.json

@@ -1,5 +1,15 @@
 {
   "images" : [
+    {
+      "idiom" : "iphone",
+      "size" : "20x20",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "iphone",
+      "size" : "20x20",
+      "scale" : "3x"
+    },
     {
       "idiom" : "iphone",
       "size" : "29x29",

Example/IGListKitExamples/SectionControllers/LabelSectionController.swift

@@ -34,7 +34,7 @@ class LabelSectionController: IGListSectionController, IGListSectionType {
     }
 
     func didUpdate(to object: Any) {
-        self.object = object as? String
+        self.object = String(describing: object)
     }
 
     func didSelectItem(at index: Int) {}

Example/IGListKitExamples/ViewControllers/LoadMoreViewController.swift

@@ -22,7 +22,7 @@ class LoadMoreViewController: UIViewController, IGListAdapterDataSource, UIScrol
     }()
     let collectionView = IGListCollectionView(frame: .zero, collectionViewLayout: UICollectionViewFlowLayout())
 
-    lazy var words = "Maecenas faucibus mollis interdum Praesent commodo cursus magna, vel scelerisque nisl consectetur et".components(separatedBy: " ")
+    lazy var items = Array(0...20)
     var loading = false
     let spinToken = NSObject()
 
@@ -42,11 +42,13 @@ class LoadMoreViewController: UIViewController, IGListAdapterDataSource, UIScrol
     //MARK: IGListAdapterDataSource
 
     func objects(for listAdapter: IGListAdapter) -> [IGListDiffable] {
-        var items: [IGListDiffable] = words as [IGListDiffable]
+        var objects = items as [IGListDiffable]
+
         if loading {
-            items.append(spinToken)
+            objects.append(spinToken)
         }
-        return items
+
+        return objects
     }
 
     func listAdapter(_ listAdapter: IGListAdapter, sectionControllerFor object: Any) -> IGListSectionController {
@@ -71,7 +73,8 @@ class LoadMoreViewController: UIViewController, IGListAdapterDataSource, UIScrol
                 sleep(2)
                 DispatchQueue.main.async {
                     self.loading = false
-                    self.words.append(contentsOf: "Etiam porta sem malesuada magna mollis euismod".components(separatedBy: " "))
+                    let itemCount = self.items.count
+                    self.items.append(contentsOf: Array(itemCount..<itemCount + 5))
                     self.adapter.performUpdates(animated: true, completion: nil)
                 }
             })

Example/IGListKitExamples/Views/SpinnerCell.swift

@@ -16,11 +16,16 @@ import UIKit
 import IGListKit
 
 func spinnerSectionController() -> IGListSingleSectionController {
-    let configureBlock = { (item: Any, cell: UICollectionViewCell) in}
+    let configureBlock = { (item: Any, cell: UICollectionViewCell) in
+        guard let cell = cell as? SpinnerCell else { return }
+        cell.activityIndicator.startAnimating()
+    }
+
     let sizeBlock = { (context: IGListCollectionContext?) -> CGSize in
-        guard let context = context else { return CGSize() }
+        guard let context = context else { return .zero }
         return CGSize(width: context.containerSize.width, height: 100)
     }
+
     return IGListSingleSectionController(cellClass: SpinnerCell.self,
                                          configureBlock: configureBlock,
                                          sizeBlock: sizeBlock)
@@ -30,7 +35,6 @@ class SpinnerCell: UICollectionViewCell {
 
     lazy var activityIndicator: UIActivityIndicatorView = {
         let view = UIActivityIndicatorView(activityIndicatorStyle: .gray)
-        view.startAnimating()
         self.contentView.addSubview(view)
         return view
     }()