three layer collection anchoring

MVMCoreUI/Atomic/Templates/CollectionTemplate.swift

@@ -79,6 +79,8 @@ import Foundation
     
     
     open override func handleNewData() {
+        topViewOutsideOfScrollArea = templateModel?.anchorHeader ?? false
+        bottomViewOutsideOfScrollArea = templateModel?.anchorFooter ?? false
         setup()
         registerCells()        
         super.handleNewData()

MVMCoreUI/BaseControllers/ProgrammaticCollectionViewController.swift

@@ -12,6 +12,8 @@ import Foundation
 @objc open class ProgrammaticCollectionViewController: ScrollingViewController {
     
     public var collectionView: UICollectionView?
+    public var topConstraint: NSLayoutConstraint?
+    public var bottomConstraint: NSLayoutConstraint?
 
     open override func loadView() {
         let view = UIView()
@@ -19,7 +21,9 @@ import Foundation
         
         let collection = createCollectionView()
         view.addSubview(collection)
-        NSLayoutConstraint.constraintPinSubview(toSuperview: collection)
+        let constraints = NSLayoutConstraint.constraintPinSubview(toSuperview: collection)
+        topConstraint = constraints?[ConstraintTop] as? NSLayoutConstraint
+        bottomConstraint = constraints?[ConstraintBot] as? NSLayoutConstraint
         
         collectionView = collection
         scrollView = collectionView

MVMCoreUI/BaseControllers/ThreeLayerCollectionViewController.swift

@@ -52,16 +52,34 @@ import Foundation
                 footerView?.topConstraint?.constant = half
                 collectionView?.collectionViewLayout.invalidateLayout()
             } else if fillTop {
-                // Only top is spaced (half the size if the bottom view is out of the scroll because it needs to be sized as if there are two spacers but there is only one.
+                // Only top is spaced.
                 headerView?.bottomConstraint?.constant = newSpace
                 collectionView?.collectionViewLayout.invalidateLayout()
             } else if fillBottom {
                 // Only bottom is spaced.
                 footerView?.topConstraint?.constant = newSpace
-                collectionView?.collectionViewLayout.invalidateLayout()
+                collectionView.collectionViewLayout.invalidateLayout()
             }
         }
     }
+    
+    func addTopViewOutside() {
+        guard let collectionView = collectionView, let topView = topView else { return }
+        view.addSubview(topView)
+        topView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
+        topView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor).isActive = true
+        view.safeAreaLayoutGuide.rightAnchor.constraint(equalTo: topView.rightAnchor).isActive = true
+        collectionView.topAnchor.constraint(equalTo: topView.bottomAnchor).isActive = true
+    }
+     
+    func addBottomViewOutside() {
+        guard let collectionView = collectionView, let bottomView = bottomView else { return }
+        view.addSubview(bottomView)
+        bottomView.topAnchor.constraint(equalTo: collectionView.bottomAnchor).isActive = true
+        bottomView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor).isActive = true
+        view.safeAreaLayoutGuide.rightAnchor.constraint(equalTo: bottomView.rightAnchor).isActive = true
+        view.safeAreaLayoutGuide.bottomAnchor.constraint(equalTo: bottomView.bottomAnchor).isActive = true
+    }
         
     //MARK: - ViewController
     open override func updateViews() {
@@ -86,8 +104,22 @@ import Foundation
 
     open override func handleNewData() {
         super.handleNewData()
+        topView?.removeFromSuperview()
+        bottomView?.removeFromSuperview()
         topView = viewForTop()
         bottomView = viewForBottom()
+        if topViewOutsideOfScrollArea {
+            topConstraint?.isActive = false
+            addTopViewOutside()
+        } else {
+            topConstraint?.isActive = true
+        }
+        if bottomViewOutsideOfScrollArea {
+            bottomConstraint?.isActive = false
+            addBottomViewOutside()
+        } else {
+            bottomConstraint?.isActive = true
+        }
         reloadCollectionData()
     }
     
@@ -176,14 +208,14 @@ import Foundation
     open func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
         if kind == UICollectionView.elementKindSectionFooter,
             let footerView = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: footerID, for: indexPath) as? ContainerCollectionReusableView {
-            let bottomView = self.bottomView ?? MVMCoreUICommonViewsUtility.getView(with: 0)
+            let bottomView = (bottomViewOutsideOfScrollArea ?  nil : self.bottomView) ?? MVMCoreUICommonViewsUtility.getView(with: 0.5)
             footerView.addAndContain(view: bottomView)
             footerView.topConstraint?.constant = spaceAboveBottomView() ?? 0
             self.footerView = footerView
             return footerView
         } else if kind == UICollectionView.elementKindSectionHeader,
             let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: headerID, for: indexPath) as? ContainerCollectionReusableView {
-            let topView = self.topView ?? MVMCoreUICommonViewsUtility.getView(with: 0)
+            let topView = (topViewOutsideOfScrollArea ?  nil : self.topView) ?? MVMCoreUICommonViewsUtility.getView(with: 0.5)
             headerView.addAndContain(view: topView)
             headerView.bottomConstraint?.constant = spaceBelowTopView() ?? 0
             self.headerView = headerView

MVMCoreUI/BaseControllers/ThreeLayerViewController.swift

@@ -117,22 +117,20 @@ extension ThreeLayerViewController {
         if let topView = viewForTop() {
             self.topView = topView
         } else {
-            topView = MVMCoreUICommonViewsUtility.commonView()
+            topView = MVMCoreUICommonViewsUtility.getView(with: 0)
-            topView?.heightAnchor.constraint(equalToConstant: 0).isActive = true
         }
         guard var topView = topView else { return nil }
         
         // Adds the top view outside the scroll if directed.
         if topViewOutsideOfScroll {
-            topConstraint?.isActive = false;
+            topConstraint?.isActive = false
             addViewOutsideOfScrollViewTop(topView)
             
             // Adds and returns an empty view to use for the internal logic.
-            topView = MVMCoreUICommonViewsUtility.commonView()
+            topView = MVMCoreUICommonViewsUtility.getView(with: 0)
-            topView.heightAnchor.constraint(equalToConstant: 0).isActive = true
             addViewInsideOfScrollViewTop(topView)
         } else {
-            topConstraint?.isActive = true;
+            topConstraint?.isActive = true
             addViewInsideOfScrollViewTop(topView)
         }
         return topView
@@ -142,8 +140,7 @@ extension ThreeLayerViewController {
         if let middleView = viewForMiddle() {
             self.middleView = middleView
         } else {
-            middleView = MVMCoreUICommonViewsUtility.commonView()
+            middleView = MVMCoreUICommonViewsUtility.getView(with: 0)
-            middleView?.heightAnchor.constraint(equalToConstant: 0).isActive = true
         }
         guard let middleView = middleView, let contentView = contentView else { return nil }
         contentView.addSubview(middleView)
@@ -157,8 +154,7 @@ extension ThreeLayerViewController {
         if let bottomView = viewForBottom() {
             self.bottomView = bottomView
         } else {
-            bottomView = MVMCoreUICommonViewsUtility.commonView()
+            bottomView = MVMCoreUICommonViewsUtility.getView(with: 0)
-            bottomView?.heightAnchor.constraint(equalToConstant: 0).isActive = true
         }
         guard var bottomView = bottomView else { return nil }
         
@@ -168,8 +164,7 @@ extension ThreeLayerViewController {
             addViewOutsideOfScrollViewBottom(bottomView)
             
             // Adds and returns an empty view to use for the internal logic.
-            bottomView = MVMCoreUICommonViewsUtility.commonView()
+            bottomView = MVMCoreUICommonViewsUtility.getView(with: 0)
-            bottomView.heightAnchor.constraint(equalToConstant: 0).isActive = true
             addViewInsideOfScrollViewBottom(bottomView)
         } else {
             bottomConstraint?.isActive = true;