Add method for reloading menu

Parchment/Classes/PagingViewController.swift

@@ -331,6 +331,22 @@ open class PagingViewController<T: PagingItem>:
 
   // MARK: Public Methods
 
+  /// Reload the data for the menu items. This method will not reload
+  /// the view controllers.
+  open func reloadMenu() {
+    let previouslySelected = state.currentPagingItem
+    let items = generateItemsForIndexedDataSource()
+    indexedDataSource?.items = items
+
+    if let pagingItem = items.first(where: { $0 == previouslySelected }) {
+      resetItems(around: pagingItem)
+    } else if let firstItem = items.first {
+      resetItems(around: firstItem)
+    } else {
+      stateMachine.fire(.removeAll)
+    }
+  }
+
   /// Reload data for all the menu items. This will keep the
   /// previously selected item if it's still part of the updated data.
   /// If not, it will select the first item in the list. This method
@@ -344,8 +360,10 @@ open class PagingViewController<T: PagingItem>:
 
     if let pagingItem = items.first(where: { $0 == previouslySelected }) {
       resetItems(around: pagingItem)
+      resetViewControllers(around: pagingItem)
     } else if let firstItem = items.first {
       resetItems(around: firstItem)
+      resetViewControllers(around: firstItem)
     } else {
       stateMachine.fire(.removeAll)
     }
@@ -363,6 +381,7 @@ open class PagingViewController<T: PagingItem>:
   open func reloadData(around pagingItem: T) {
     indexedDataSource?.items = generateItemsForIndexedDataSource()
     resetItems(around: pagingItem)
+    resetViewControllers(around: pagingItem)
   }
 
   /// Selects a given paging item. This need to be called after you
@@ -787,11 +806,13 @@ open class PagingViewController<T: PagingItem>:
     stateMachine.fire(.reset(pagingItem: pagingItem))
     collectionView.reloadData()
 
+    configureSizeCache(for: pagingItem)
+  }
+
+  private func resetViewControllers(around pagingItem: T) {
     pageViewController.removeAllViewControllers()
     selectViewController(pagingItem, direction: .none, animated: false)
 
-    configureSizeCache(for: pagingItem)
-
     // Reloading the data triggers the didFinishScrollingFrom delegate
     // to be called which in turn means the wrong item will be selected.
     // For now, we just fix this by selecting the correct item manually.

ParchmentTests/PagingViewControllerSpec.swift

@@ -79,6 +79,72 @@ class PagingViewControllerSpec: QuickSpec {
 
     describe("PagingViewController") {
 
+      describe("reloading menu") {
+
+        let dataSource = ReloadingDataSource()
+        var pagingViewController: PagingViewController<PagingIndexItem>!
+        var viewController0: UIViewController!
+        var viewController1: UIViewController!
+
+        beforeEach {
+          viewController0 = UIViewController()
+          viewController1 = UIViewController()
+
+          dataSource.viewControllers = [
+            viewController0,
+            viewController1
+          ]
+
+          dataSource.items = [
+            PagingIndexItem(index: 0, title: "0"),
+            PagingIndexItem(index: 1, title: "1")
+          ]
+
+          pagingViewController = PagingViewController()
+          pagingViewController.menuItemSize = .fixed(width: 100, height: 50)
+          pagingViewController.dataSource = dataSource
+
+          UIApplication.shared.keyWindow!.rootViewController = pagingViewController
+          let _ = pagingViewController.view
+
+          pagingViewController.collectionView.bounds = CGRect(x: 0, y: 0, width: 1000, height: 50)
+          pagingViewController.viewDidLayoutSubviews()
+        }
+
+        it("reload the menu items") {
+          let item2 = PagingIndexItem(index: 0, title: "2")
+          let item3 = PagingIndexItem(index: 1, title: "3")
+
+          dataSource.items = [item2, item3]
+          pagingViewController.reloadMenu()
+          pagingViewController.view.layoutIfNeeded()
+
+          let cell2 = pagingViewController.collectionView.cellForItem(
+            at: IndexPath(item: 0, section: 0)
+          ) as? PagingTitleCell
+          let cell3 = pagingViewController.collectionView.cellForItem(
+            at: IndexPath(item: 1, section: 0)
+          ) as? PagingTitleCell
+
+          expect(pagingViewController.collectionView.numberOfItems(inSection: 0)).to(equal(2))
+          expect(cell2?.titleLabel.text).to(equal("2"))
+          expect(cell3?.titleLabel.text).to(equal("3"))
+        }
+
+        it("does not reload the view controllers") {
+          let viewController2 = UIViewController()
+          let viewController3 = UIViewController()
+
+          dataSource.viewControllers = [viewController2, viewController3]
+          pagingViewController.reloadMenu()
+
+          let pageViewController = pagingViewController.pageViewController
+          expect(pageViewController.selectedViewController).to(be(viewController0))
+          expect(pageViewController.afterViewController).to(be(viewController1))
+        }
+
+      }
+
       describe("reloading data") {
 
         let dataSource = ReloadingDataSource()

README.md

@@ -147,7 +147,12 @@ func reloadData()
 This will keep the previously selected item if it's still part of the
 updated data. If not, it will select the first item in the list. It
 will also reload the view controllers displayed in the page view
-controller.
+controller. If you only want to reload the menu items, you can use
+this method:
+
+```Swift
+func reloadMenu()
+```
 
 Calling `reloadData()` will not work when using
 `PagingViewControllerInfiniteDataSource`, as we then need to know what