Merge pull request xmartlabs#367 from xmartlabs/fix/issue-357

Fixes xmartlabs#357

Author: pera

Sources/ButtonBarPagerTabStripViewController.swift

@@ -266,7 +266,7 @@ open class ButtonBarPagerTabStripViewController: PagerTabStripViewController, Pa
         return cells
     }
 
-    // MARK: - UICollectionViewDelegateFlowLayut
+    // MARK: - UICollectionViewDelegateFlowLayout
 
     open func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: IndexPath) -> CGSize {
         guard let cellWidthValue = cachedCellWidths?[indexPath.row] else {

Sources/PagerTabStripViewController.swift

@@ -62,6 +62,7 @@ open class PagerTabStripViewController: UIViewController, UIScrollViewDelegate {
 
     open private(set) var viewControllers = [UIViewController]()
     open private(set) var currentIndex = 0
+    open private(set) var preCurrentIndex = 0 // used *only* to store the index to which move when the pager becomes visible
 
     open var pageWidth: CGFloat {
         return containerView.bounds.width
@@ -123,6 +124,10 @@ open class PagerTabStripViewController: UIViewController, UIScrollViewDelegate {
         super.viewDidAppear(animated)
         lastSize = containerView.bounds.size
         updateIfNeeded()
+        let needToUpdateCurrentChild = preCurrentIndex != currentIndex
+        if needToUpdateCurrentChild {
+            moveToViewController(at: preCurrentIndex)
+        }
         isViewAppearing = false
         childViewControllers.forEach { $0.endAppearanceTransition() }
     }
@@ -148,9 +153,10 @@ open class PagerTabStripViewController: UIViewController, UIScrollViewDelegate {
 
     open func moveToViewController(at index: Int, animated: Bool = true) {
         guard isViewLoaded && view.window != nil && currentIndex != index else {
-            currentIndex = index
+            preCurrentIndex = index
             return
         }
+        
         if animated && pagerBehaviour.skipIntermediateViewControllers && abs(currentIndex - index) > 1 {
             var tmpViewControllers = viewControllers
             let currentChildVC = viewControllers[currentIndex]
@@ -268,6 +274,7 @@ open class PagerTabStripViewController: UIViewController, UIScrollViewDelegate {
         let virtualPage = virtualPageFor(contentOffset: containerView.contentOffset.x)
         let newCurrentIndex = pageFor(virtualPage: virtualPage)
         currentIndex = newCurrentIndex
+        preCurrentIndex = currentIndex
         let changeCurrentIndex = newCurrentIndex != oldCurrentIndex
 
         if let progressiveDeledate = self as? PagerTabStripIsProgressiveDelegate, pagerBehaviour.isProgressiveIndicator {
@@ -296,6 +303,7 @@ open class PagerTabStripViewController: UIViewController, UIScrollViewDelegate {
         if currentIndex >= viewControllers.count {
             currentIndex = viewControllers.count - 1
         }
+        preCurrentIndex = currentIndex
         containerView.contentOffset = CGPoint(x: pageOffsetForChild(at: currentIndex), y: 0)
         updateContent()
     }
@@ -333,6 +341,7 @@ open class PagerTabStripViewController: UIViewController, UIScrollViewDelegate {
             guard let me = self else { return }
             me.isViewRotating = false
             me.currentIndex = me.pageBeforeRotate
+            me.preCurrentIndex = me.currentIndex
             me.updateIfNeeded()
         }
     }