Add minimumItemsToScroll functionality (#46)

* Add minimumItemsToScroll functionality

* Added minimumItemsToScroll, bumped version number to 1.3.0

Author: Oliver Mastny

Example/Podfile.lock

@@ -1,5 +1,5 @@
 PODS:
-  - MSPeekCollectionViewDelegateImplementation (1.2.2)
+  - MSPeekCollectionViewDelegateImplementation (1.3.0)
 
 DEPENDENCIES:
   - MSPeekCollectionViewDelegateImplementation (from `../`)
@@ -9,7 +9,7 @@ EXTERNAL SOURCES:
     :path: "../"
 
 SPEC CHECKSUMS:
-  MSPeekCollectionViewDelegateImplementation: dc9c3aa660f03c4b2bb84edb1144c87ba562915e
+  MSPeekCollectionViewDelegateImplementation: 09fdbcd804848033804ee66ce93ac9a0ebba8262
 
 PODFILE CHECKSUM: 8d230cee08c8a8b7e62859eff8016277efe2311d
 

Example/Pods/Local Podspecs/MSPeekCollectionViewDelegateImplementation.podspec.json

@@ -144,6 +144,13 @@ class HorizontalScrollDirectionTests: XCTestCase {
         XCTAssertEqual(simulatedTargetContentOffset.pointee.x, 520)
     }
 
+    func test_MinimumItemsToScroll_ShouldScrollProperly() {
+        collectionView.frame = CGRect(x: 0, y: 0, width: 320, height: 200)
+        sut = MSPeekCollectionViewDelegateImplementation(cellSpacing: 20, cellPeekWidth: 20, scrollThreshold: 50, minimumItemsToScroll: 2, maximumItemsToScroll: 4)
+        let simulatedTargetContentOffset = simulateHorizontalScroll(distance: 51)
+        XCTAssertEqual(simulatedTargetContentOffset.pointee.x, 520)
+    }
+    
     func test_contentOffsetAtIndex_ShouldReturnCorrectOffset() {
         collectionView.frame = CGRect(x: 0, y: 0, width: 320, height: 200)
         sut = MSPeekCollectionViewDelegateImplementation(cellSpacing: 20, cellPeekWidth: 20, scrollThreshold: 50, maximumItemsToScroll: 2)

Example/Pods/Manifest.lock

@@ -126,6 +126,14 @@ class VerticalScrollDirectionTests: XCTestCase {
         XCTAssertEqual(simulatedTargetContentOffset.pointee.y, 280)
     }
 
+    
+    func test_MinimumItemsToScroll_ShouldScrollProperly() {
+        collectionView.frame = CGRect(x: 0, y: 0, width: 320, height: 200)
+        sut = MSPeekCollectionViewDelegateImplementation(cellSpacing: 20, cellPeekWidth: 20, scrollThreshold: 50, minimumItemsToScroll: 2, maximumItemsToScroll: 4, scrollDirection: .vertical)
+        let simulatedTargetContentOffset = simulateVerticalScroll(distance: 51)
+        XCTAssertEqual(simulatedTargetContentOffset.pointee.y, 280)
+    }
+    
     func test_contentOffsetAtIndex_ShouldReturnCorrectOffset() {
         collectionView.frame = CGRect(x: 0, y: 0, width: 320, height: 200)
         sut = MSPeekCollectionViewDelegateImplementation(cellSpacing: 20, cellPeekWidth: 20, scrollThreshold: 50, maximumItemsToScroll: 2, scrollDirection: .vertical)

Example/Pods/Target Support Files/MSPeekCollectionViewDelegateImplementation/MSPeekCollectionViewDelegateImplementation-Info.plist

@@ -8,7 +8,7 @@
 
 Pod::Spec.new do |s|
   s.name             = 'MSPeekCollectionViewDelegateImplementation'
-  s.version          = '1.2.2'
+  s.version          = '1.3.0'
   s.summary          = 'A custom paging behavior that peeks the previous and next items in a collection view'
   s.swift_version    = '4.2'
 

Example/Tests/HorizontalScrollDirectionTests.swift

@@ -33,6 +33,7 @@ open class MSPeekCollectionViewDelegateImplementation: NSObject {
     public let cellPeekWidth: CGFloat
     public let cellSpacing: CGFloat
     public let scrollThreshold: CGFloat
+    public let minimumItemsToScroll: Int
     public let maximumItemsToScroll: Int
     public let numberOfItemsToShow: Int
     public let scrollDirection: UICollectionView.ScrollDirection
@@ -55,10 +56,11 @@ open class MSPeekCollectionViewDelegateImplementation: NSObject {
         return max(0, finalWidth)
     }
 
-    public init(cellSpacing: CGFloat = 20, cellPeekWidth: CGFloat = 20, scrollThreshold: CGFloat = 50, maximumItemsToScroll: Int = 1, numberOfItemsToShow: Int = 1, scrollDirection: UICollectionView.ScrollDirection = .horizontal) {
+    public init(cellSpacing: CGFloat = 20, cellPeekWidth: CGFloat = 20, scrollThreshold: CGFloat = 50, minimumItemsToScroll: Int = 1, maximumItemsToScroll: Int = 1, numberOfItemsToShow: Int = 1, scrollDirection: UICollectionView.ScrollDirection = .horizontal) {
         self.cellSpacing = cellSpacing
         self.cellPeekWidth = cellPeekWidth
         self.scrollThreshold = scrollThreshold
+        self.minimumItemsToScroll = minimumItemsToScroll
         self.maximumItemsToScroll = maximumItemsToScroll
         self.numberOfItemsToShow = numberOfItemsToShow
         self.scrollDirection = scrollDirection
@@ -91,6 +93,12 @@ open class MSPeekCollectionViewDelegateImplementation: NSObject {
             coefficent = Int(scrollDistance/scrollWidth)
         }
 
+        if coefficent > 0 {
+            coefficent = max(minimumItemsToScroll, coefficent)
+        } else if coefficent < 0 {
+            coefficent = min(-minimumItemsToScroll, coefficent)
+        }
+        
         let finalCoefficent = max((-1) * maximumItemsToScroll, min(coefficent, maximumItemsToScroll))
         return finalCoefficent
     }

Example/Tests/VerticalScrollDirectionTests.swift

@@ -72,6 +72,10 @@ delegate = MSPeekCollectionViewDelegateImplementation(cellPeekWidth: 20)
 delegate = MSPeekCollectionViewDelegateImplementation(scrollThreshold: 150)
 ```
 ```swift
+//minimumItemsToScroll is the minimum number of items that can be scrolled
+delegate = MSPeekCollectionViewDelegateImplementation(minimumItemsToScroll: 1)
+```
+```swift
 //maximumItemsToScroll is the maximum number of items that can be scrolled if the scroll distance is large
 delegate = MSPeekCollectionViewDelegateImplementation(maximumItemsToScroll: 3)
 ```