Improve diffing (#11)

* improved diffing by using onBindViewHolder with payload
* fixed crash when transitioning from empty item to the first one.
* improved empty item handling, notifying item change only when it's the first position. 
* enhanced demo app 
* updated readme.

README.md

@@ -36,7 +36,7 @@ In this way every item of the recycler view has its own set of files, resulting
 ## <a name="setup"></a>Setup
 In your gradle dependencies add:
 ```groovy
-def recyclerAdapterVersion = "2.4.2"
+def recyclerAdapterVersion = "2.5.0"
 implementation "net.gotev:recycleradapter:$recyclerAdapterVersion"
 ```
 
@@ -76,7 +76,9 @@ open class ExampleItem(private val context: Context, private val text: String)
 
     override fun getLayoutId() = R.layout.item_example
 
-    override fun bind(holder: ExampleItem.Holder) {
+    override fun bind(firstTime: Boolean, holder: ExampleItem.Holder) {
+        // you can use firstTime to discriminate between bindings you
+        // need only the first time the item is binded from the others
         holder.titleField.text = text
     }
 
@@ -294,7 +296,7 @@ open class ExampleItem(private val context: Context, private val text: String)
 
     override fun onFilter(searchTerm: String) = text.contains(searchTerm)
 
-    override fun bind(holder: Holder) {
+    override fun bind(firstTime: Boolean, holder: Holder) {
         holder.titleField.text = text
         holder.subtitleField.text = "subtitle"
     }
@@ -396,7 +398,7 @@ class TextWithButtonItem(private val text: String) : AdapterItem<TextWithButtonI
 
     override fun diffingId() = javaClass.name + text
 
-    override fun bind(holder: Holder) {
+    override fun bind(firstTime: Boolean, holder: Holder) {
         holder.textViewField.text = text
         holder.buttonField.isChecked = pressed
     }

app/demo/src/main/java/net/gotev/recycleradapterdemo/activities/SelectionActivity.kt

@@ -44,6 +44,7 @@ class SelectionActivity : AppCompatActivity() {
         recyclerAdapter.setEmptyItem(LabelItem(getString(R.string.empty_list)))
 
         recycler_view.apply {
+            itemAnimator?.changeDuration = 0
             layoutManager = LinearLayoutManager(context, RecyclerView.VERTICAL, false)
             adapter = recyclerAdapter
         }

app/demo/src/main/java/net/gotev/recycleradapterdemo/activities/SyncActivity.kt

@@ -50,6 +50,11 @@ class SyncActivity : AppCompatActivity() {
                     SyncItem(2, "listA")
             )
 
+    private fun listC() =
+            arrayListOf(
+                    SyncItem(1, "listC")
+            )
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_sync)
@@ -85,6 +90,14 @@ class SyncActivity : AppCompatActivity() {
             recyclerAdapter.syncWithItems(listB())
         }
 
+        syncC.setOnClickListener {
+            recyclerAdapter.syncWithItems(listC())
+        }
+
+        empty.setOnClickListener {
+            recyclerAdapter.clear()
+        }
+
         shuffle.setOnClickListener {
             scheduledOperation = if (scheduledOperation == null) {
                 shuffle.text = getString(R.string.button_shuffle_stop)

app/demo/src/main/java/net/gotev/recycleradapterdemo/adapteritems/LabelItem.kt

@@ -17,7 +17,7 @@ class LabelItem(private val text: String, private val selectionGroup: String? =
 
     override fun getSelectionGroup() = selectionGroup
 
-    override fun bind(holder: Holder) {
+    override fun bind(firstTime: Boolean, holder: Holder) {
         holder.textViewField.text = text
     }
 

app/demo/src/main/java/net/gotev/recycleradapterdemo/adapteritems/SelectableItem.kt

@@ -26,7 +26,7 @@ open class SelectableItem(val label: String, private val group: String)
         return super.onSelectionChanged(isNowSelected)
     }
 
-    override fun bind(holder: Holder) {
+    override fun bind(firstTime: Boolean, holder: Holder) {
         holder.toggleField.apply {
             isChecked = selected
             text = label

app/demo/src/main/java/net/gotev/recycleradapterdemo/adapteritems/TextWithToggleItem.kt

@@ -28,7 +28,7 @@ class TextWithToggleItem(private val text: String) : AdapterItem<TextWithToggleI
 
     override fun onFilter(searchTerm: String) = text.contains(searchTerm, ignoreCase = true)
 
-    override fun bind(holder: Holder) {
+    override fun bind(firstTime: Boolean, holder: Holder) {
         holder.textViewField.text = text
         holder.buttonField.isChecked = pressed
     }

app/demo/src/main/java/net/gotev/recycleradapterdemo/adapteritems/TitleSubtitleItem.kt

@@ -20,7 +20,7 @@ open class TitleSubtitleItem(private val title: String, private val subtitle: St
 
     override fun onFilter(searchTerm: String) = title.contains(searchTerm, ignoreCase = true)
 
-    override fun bind(holder: Holder) {
+    override fun bind(firstTime: Boolean, holder: Holder) {
         holder.titleField.text = title
         holder.subtitleField.text = subtitle
     }

app/demo/src/main/java/net/gotev/recycleradapterdemo/adapteritems/TitledCarousel.kt

@@ -20,8 +20,8 @@ class TitledCarousel(
 
     override fun getLayoutId() = R.layout.item_titled_carousel
 
-    override fun bind(holder: Holder) {
-        super.bind(holder)
+    override fun bind(firstTime: Boolean, holder: Holder) {
+        super.bind(firstTime, holder)
         holder.title.text = title
     }
 

app/demo/src/main/java/net/gotev/recycleradapterdemo/adapteritems/leavebehind/MyLeaveBehindItem.kt

@@ -12,7 +12,7 @@ class MyLeaveBehindItem(private val value: String, private val background: Strin
 
     override fun onFilter(searchTerm: String) = value.contains(searchTerm, ignoreCase = true)
 
-    override fun bind(holder: Holder) {
+    override fun bind(firstTime: Boolean, holder: Holder) {
         holder.nameField.text = value
         holder.deleteField.text = background
     }

app/demo/src/main/java/net/gotev/recycleradapterdemo/paging/PagingHelper.kt

@@ -36,7 +36,7 @@ private class PagedRecyclerAdapter
             adapter.onCreateViewHolder(parent, viewType)
 
     override fun onBindViewHolder(holder: RecyclerAdapterViewHolder, position: Int) =
-            (getItem(position) as AdapterItem<RecyclerAdapterViewHolder>).bind(holder)
+            (getItem(position) as AdapterItem<RecyclerAdapterViewHolder>).bind(true, holder)
 
     override fun submitList(pagedList: PagedList<AdapterItem<*>>?) {
         if (viewType == null) {

app/demo/src/main/res/layout/activity_sync.xml

@@ -7,6 +7,17 @@
     android:layout_height="match_parent"
     tools:context="net.gotev.recycleradapterdemo.activities.MainActivity">
 
+    <com.google.android.material.button.MaterialButton
+        android:id="@+id/empty"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="@dimen/spacer_default"
+        android:layout_marginBottom="@dimen/spacer_default"
+        android:text="@string/button_empty"
+        app:layout_constraintTop_toTopOf="parent"
+        app:layout_constraintLeft_toLeftOf="parent"
+        app:layout_constraintStart_toStartOf="parent" />
+
     <androidx.recyclerview.widget.RecyclerView
         android:id="@+id/recycler_view"
         android:layout_width="0dp"
@@ -16,7 +27,7 @@
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintLeft_toLeftOf="parent"
         app:layout_constraintStart_toStartOf="parent"
-        app:layout_constraintTop_toTopOf="parent" />
+        app:layout_constraintTop_toBottomOf="@+id/empty" />
 
     <com.google.android.material.button.MaterialButton
         android:id="@+id/shuffle"
@@ -50,4 +61,14 @@
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintLeft_toRightOf="@id/syncA" />
 
+    <com.google.android.material.button.MaterialButton
+        android:id="@+id/syncC"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="@dimen/spacer_default"
+        android:layout_marginBottom="@dimen/spacer_default"
+        android:text="@string/button_sync_group_c"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintLeft_toRightOf="@id/syncB" />
+
 </androidx.constraintlayout.widget.ConstraintLayout>

app/demo/src/main/res/values/strings.xml

@@ -14,10 +14,12 @@
     <string name="multiple_selection">Group with multiple selection</string>
     <string name="show_selections">Show Selections</string>
     <string name="search_hint">Search…</string>
-    <string name="button_shuffle_start">Start Shuffle</string>
-    <string name="button_shuffle_stop">Stop Shuffle</string>
+    <string name="button_shuffle_start">Shuffle</string>
+    <string name="button_shuffle_stop">Stop</string>
     <string name="button_sync_group_a">Sync A</string>
     <string name="button_sync_group_b">Sync B</string>
+    <string name="button_sync_group_c">Sync C</string>
+    <string name="button_empty">Empty list</string>
     <string name="infinite_scrolling">Infinite Scrolling</string>
     <string name="carousels_plain">Carousels (plain)</string>
     <string name="carousels_pool">Carousels (with pool)</string>

manifest.gradle

@@ -9,7 +9,7 @@ ext {
     library_licenses = ["Apache-2.0"]
     library_licenses_url = 'http://www.apache.org/licenses/LICENSE-2.0.txt'
     library_project_group = 'net.gotev'
-    library_version = '2.4.2'
+    library_version = '2.5.0'
     version_code = 5
     min_sdk = 18
     target_sdk = 28

recycleradapter-extensions/src/main/java/net/gotev/recycleradapter/ext/NestedRecyclerAdapterItem.kt

@@ -22,7 +22,7 @@ abstract class NestedRecyclerAdapterItem<T : NestedRecyclerAdapterItem.Holder>(
     open fun getLayoutManager(context: Context): RecyclerView.LayoutManager =
             LinearLayoutManager(context, HORIZONTAL, false)
 
-    override fun bind(holder: T) {
+    override fun bind(firstTime: Boolean, holder: T) {
         with(holder.recyclerView) {
             // reset layout manager and adapter
             layoutManager = null

recycleradapter/src/main/java/net/gotev/recycleradapter/AdapterItem.kt

@@ -82,10 +82,7 @@ abstract class AdapterItem<T : RecyclerAdapterViewHolder> : Comparable<AdapterIt
         // hierarchy is present, as the first one should be the last of the subclasses
         for (cl in javaClass.classes) {
             if (RecyclerAdapterViewHolder::class.java.isAssignableFrom(cl)) {
-                val clazz = cl as Class<T>
-                val holder = clazz.getConstructor(View::class.java).newInstance(view)
-                onHolderCreated(holder)
-                return holder
+                return (cl as Class<T>).getConstructor(View::class.java).newInstance(view)
             }
         }
 
@@ -95,17 +92,12 @@ abstract class AdapterItem<T : RecyclerAdapterViewHolder> : Comparable<AdapterIt
 
     }
 
-    /**
-     * Perform initialization stuff on the holder. This is done only once after the holder has
-     * been created.
-     */
-    open fun onHolderCreated(holder: T) {}
-
     /**
      * Bind the current item with the view
+     * @param firstTime true if it's the first time this item is being bound
      * @param holder ViewHolder on which to bind data
      */
-    abstract fun bind(holder: T)
+    abstract fun bind(firstTime: Boolean, holder: T)
 
     /**
      * Returns the ID of this item's selection group. By default it's null.

recycleradapter/src/main/java/net/gotev/recycleradapter/RecyclerAdapter.kt

@@ -99,6 +99,10 @@ class RecyclerAdapter : RecyclerView.Adapter<RecyclerAdapterViewHolder>(), Recyc
         setHasStableIds(true)
     }
 
+    private fun notifyChangedPosition(position: Int) {
+        notifyItemChanged(position, true)
+    }
+
     @Suppress("UNCHECKED_CAST")
     private fun <T : RecyclerAdapterViewHolder> AdapterItem<out T>.castAsIn(): AdapterItem<in T> {
         return this as AdapterItem<in T>
@@ -110,7 +114,7 @@ class RecyclerAdapter : RecyclerView.Adapter<RecyclerAdapterViewHolder>(), Recyc
         this.let {
             selected = newStatus
             if (onSelectionChanged(isNowSelected = newStatus)) {
-                notifyItemChanged(position)
+                notifyChangedPosition(position)
             }
         }
     }
@@ -120,7 +124,7 @@ class RecyclerAdapter : RecyclerView.Adapter<RecyclerAdapterViewHolder>(), Recyc
     private fun updateItemAtPosition(item: AdapterItem<in RecyclerAdapterViewHolder>,
                                      position: Int) {
         items[position] = item
-        notifyItemChanged(position)
+        notifyChangedPosition(position)
     }
 
     private fun registerItemType(item: AdapterItem<*>) {
@@ -131,10 +135,10 @@ class RecyclerAdapter : RecyclerView.Adapter<RecyclerAdapterViewHolder>(), Recyc
         }
     }
 
-    private fun removeEmptyItemIfItHasBeenConfigured() {
+    private fun removeEmptyItemIfItHasBeenConfigured(insertPosition: Int) {
         // this is necessary to prevent IndexOutOfBoundsException on RecyclerView when the
         // first item gets added and an empty item has been configured
-        if (items.size >= 1 && emptyItem != null) {
+        if (insertPosition == 0 && items.size >= 1 && emptyItem != null) {
             notifyItemChanged(0)
         }
     }
@@ -163,15 +167,23 @@ class RecyclerAdapter : RecyclerView.Adapter<RecyclerAdapterViewHolder>(), Recyc
         return createItemViewHolder(parent, item)
     }
 
-    override fun onBindViewHolder(holder: RecyclerAdapterViewHolder, position: Int) {
+    private fun bindItem(holder: RecyclerAdapterViewHolder, position: Int, firstTime: Boolean) {
         val item = if (adapterIsEmptyAndEmptyItemIsDefined()) {
             emptyItem!!
         } else {
             items[position]
         }
 
         holder.setAdapter(this)
-        item.bind(holder)
+        item.bind(firstTime, holder)
+    }
+
+    override fun onBindViewHolder(holder: RecyclerAdapterViewHolder, position: Int, payloads: MutableList<Any>) {
+        bindItem(holder, position, payloads.isEmpty())
+    }
+
+    override fun onBindViewHolder(holder: RecyclerAdapterViewHolder, position: Int) {
+        bindItem(holder, position, true)
     }
 
     override fun getItemCount() = if (adapterIsEmptyAndEmptyItemIsDefined()) 1 else items.size
@@ -199,7 +211,7 @@ class RecyclerAdapter : RecyclerView.Adapter<RecyclerAdapterViewHolder>(), Recyc
     override fun notifyItemChanged(holder: RecyclerAdapterViewHolder) {
         val position = holder.adapterPosition.takeIf { !it.isOutOfItemsRange() } ?: return
 
-        notifyItemChanged(position)
+        notifyChangedPosition(position)
     }
 
     private fun selectItemAtPosition(position: Int) {
@@ -301,7 +313,7 @@ class RecyclerAdapter : RecyclerView.Adapter<RecyclerAdapterViewHolder>(), Recyc
         }
 
         registerItemType(item)
-        removeEmptyItemIfItHasBeenConfigured()
+        removeEmptyItemIfItHasBeenConfigured(insertPosition)
         notifyItemInserted(insertPosition)
         return this
     }
@@ -336,7 +348,7 @@ class RecyclerAdapter : RecyclerView.Adapter<RecyclerAdapterViewHolder>(), Recyc
             }
         }
 
-        removeEmptyItemIfItHasBeenConfigured()
+        removeEmptyItemIfItHasBeenConfigured(firstIndex)
         notifyItemRangeInserted(firstIndex, newItems.size)
         return this
     }
@@ -433,8 +445,8 @@ class RecyclerAdapter : RecyclerView.Adapter<RecyclerAdapterViewHolder>(), Recyc
                     } else {
                         items[internalItemIndex] = newItem.castAsIn()
                         registerItemType(newItem)
-                        removeEmptyItemIfItHasBeenConfigured()
-                        notifyItemChanged(internalItemIndex)
+                        removeEmptyItemIfItHasBeenConfigured(internalItemIndex)
+                        notifyChangedPosition(internalItemIndex)
                     }
                 } else {
                     if (internalItemIndex != newItemsIndex) {