focus the proper portrait photo at swiping the stripe

app/src/main/kotlin/com/simplemobiletools/gallery/pro/adapters/PortraitPhotosAdapter.kt

@@ -19,6 +19,7 @@ class PortraitPhotosAdapter(val context: Context, val photos: ArrayList<String>,
         RecyclerView.Adapter<PortraitPhotosAdapter.ViewHolder>() {
 
     var currentSelectionIndex = -1
+    var views = HashMap<Int, View>()
     private var strokeBackground = context.resources.getDrawable(R.drawable.stroke_background)
     private val itemWidth = context.resources.getDimension(R.dimen.portrait_photos_stripe_height).toInt()
 
@@ -37,9 +38,14 @@ class PortraitPhotosAdapter(val context: Context, val photos: ArrayList<String>,
         if (currentSelectionIndex != position) {
             currentSelectionIndex = position
             notifyDataSetChanged()
+            views[position]?.performClick()
         }
     }
 
+    fun performClickOn(position: Int) {
+        views[position]?.performClick()
+    }
+
     inner class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
         fun bindView(photo: String, position: Int): View {
             itemView.apply {
@@ -67,6 +73,7 @@ class PortraitPhotosAdapter(val context: Context, val photos: ArrayList<String>,
                         .into(portrait_photo_item_thumbnail)
 
                 if (photo.isNotEmpty()) {
+                    views[position] = this
                     setOnClickListener {
                         itemClick(position, x.toInt())
                         setCurrentPhoto(position)

app/src/main/kotlin/com/simplemobiletools/gallery/pro/fragments/PhotoFragment.kt

@@ -16,6 +16,7 @@ import android.os.Bundle
 import android.os.Handler
 import android.util.DisplayMetrics
 import android.view.LayoutInflater
+import android.view.MotionEvent
 import android.view.View
 import android.view.ViewGroup
 import android.widget.RelativeLayout
@@ -470,6 +471,8 @@ class PhotoFragment : ViewPagerFragment() {
             setupStripeBottomMargin()
 
             val coverIndex = getCoverImageIndex(paths)
+            setupStripeUpListener(adapter, screenWidth, itemWidth)
+
             mView.photo_portrait_stripe.onGlobalLayout {
                 mView.photo_portrait_stripe.scrollBy((coverIndex - fakeItemsCnt) * itemWidth, 0)
                 adapter.setCurrentPhoto(coverIndex)
@@ -520,6 +523,28 @@ class PhotoFragment : ViewPagerFragment() {
         return coverIndex
     }
 
+    private fun setupStripeUpListener(adapter: PortraitPhotosAdapter, screenWidth: Int, itemWidth: Int) {
+        mView.photo_portrait_stripe.setOnTouchListener { v, event ->
+            if (event.action == MotionEvent.ACTION_UP || event.action == MotionEvent.ACTION_CANCEL) {
+                var closestIndex = -1
+                var closestDistance = Integer.MAX_VALUE
+                val center = screenWidth / 2
+                for ((key, value) in adapter.views) {
+                    val distance = Math.abs(value.x.toInt() + itemWidth / 2 - center)
+                    if (distance < closestDistance) {
+                        closestDistance = distance
+                        closestIndex = key
+                    }
+                }
+
+                Handler().postDelayed({
+                    adapter.performClickOn(closestIndex)
+                }, 100)
+            }
+            false
+        }
+    }
+
     private fun openPanorama() {
         Intent(context, PanoramaPhotoActivity::class.java).apply {
             putExtra(PATH, mMedium.path)