#3772 Convert SearchImagesFragment to use Pagination - allow viewpager to load more data

app/src/main/java/fr/free/nrw/commons/explore/BaseSearchFragment.kt

@@ -51,7 +51,8 @@ abstract class BaseSearchFragment<T> : CommonsDaggerSupportFragment(),
     override fun observeSearchResults(searchResults: LiveData<PagedList<T>>) {
         this.searchResults?.removeObservers(viewLifecycleOwner)
         this.searchResults = searchResults
-        searchResults.observe(viewLifecycleOwner, Observer(pagedListAdapter::submitList))
+        searchResults.observe(viewLifecycleOwner, Observer {
+            pagedListAdapter.submitList(it) })
     }
 
     override fun onAttach(context: Context) {

app/src/main/java/fr/free/nrw/commons/explore/media/SearchMediaFragment.kt

@@ -1,5 +1,7 @@
 package fr.free.nrw.commons.explore.media
 
+import android.os.Bundle
+import android.view.View
 import fr.free.nrw.commons.Media
 import fr.free.nrw.commons.R
 import fr.free.nrw.commons.explore.BaseSearchFragment
@@ -26,12 +28,30 @@ class SearchMediaFragment : BaseSearchFragment<Media>(), SearchMediaFragmentCont
         }
     }
 
+    private val simpleDataObserver = SimpleDataObserver { notifyViewPager() }
+
     fun requestMoreImages() {
-        // This paradigm is not well suited to pagination
+        // This functionality is replaced by a dataSetObserver and by using loadAround
+    }
+
+    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+        super.onViewCreated(view, savedInstanceState)
+        pagedListAdapter.registerAdapterDataObserver(simpleDataObserver)
+    }
+
+    override fun onDestroyView() {
+        super.onDestroyView()
+        pagedListAdapter.unregisterAdapterDataObserver(simpleDataObserver)
+    }
+
+    private fun notifyViewPager() {
+        (activity as SearchActivity).viewPagerNotifyDataSetChanged()
     }
 
     fun getImageAtPosition(position: Int): Media? =
         pagedListAdapter.currentList?.get(position)?.takeIf { it.filename != null }
+            .also { pagedListAdapter.currentList?.loadAround(position) }
 
     fun getTotalImagesCount(): Int = pagedListAdapter.itemCount
 }
+

app/src/main/java/fr/free/nrw/commons/explore/media/SimpleDataObserver.kt

@@ -0,0 +1,40 @@
+package fr.free.nrw.commons.explore.media
+
+import androidx.recyclerview.widget.RecyclerView
+
+class SimpleDataObserver(private val onAnyChange: () -> Unit) : RecyclerView.AdapterDataObserver() {
+    override fun onChanged() {
+        super.onChanged()
+        onAnyChange.invoke()
+    }
+
+    override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
+        super.onItemRangeRemoved(positionStart, itemCount)
+        onAnyChange.invoke()
+    }
+
+    override fun onItemRangeMoved(fromPosition: Int, toPosition: Int, itemCount: Int) {
+        super.onItemRangeMoved(fromPosition, toPosition, itemCount)
+        onAnyChange.invoke()
+    }
+
+    override fun onStateRestorationPolicyChanged() {
+        super.onStateRestorationPolicyChanged()
+        onAnyChange.invoke()
+    }
+
+    override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
+        super.onItemRangeInserted(positionStart, itemCount)
+        onAnyChange.invoke()
+    }
+
+    override fun onItemRangeChanged(positionStart: Int, itemCount: Int) {
+        super.onItemRangeChanged(positionStart, itemCount)
+        onAnyChange.invoke()
+    }
+
+    override fun onItemRangeChanged(positionStart: Int, itemCount: Int, payload: Any?) {
+        super.onItemRangeChanged(positionStart, itemCount, payload)
+        onAnyChange.invoke()
+    }
+}