wordpress-mobile · kwonye · Oct 25, 2018 · Oct 17, 2018 · Oct 17, 2018 · Oct 17, 2018
diff --git a/WordPress/build.gradle b/WordPress/build.gradle
@@ -153,6 +153,7 @@ dependencies {
     implementation 'com.squareup.okio:okio:1.13.0'
     implementation 'org.apache.commons:commons-text:1.1'
     implementation 'com.airbnb.android:lottie:2.0.0-rc2'
+    implementation 'com.facebook.shimmer:shimmer:0.3.0'
 
     implementation ('com.yalantis:ucrop:2.2.0') {
         exclude group: 'com.squareup.okhttp3'

diff --git a/WordPress/src/main/java/org/wordpress/android/ui/ListManagerDiffCallback.kt b/WordPress/src/main/java/org/wordpress/android/ui/ListManagerDiffCallback.kt
@@ -0,0 +1,67 @@
+package org.wordpress.android.ui
+
+import android.support.v7.util.DiffUtil
+import org.wordpress.android.fluxc.model.list.ListManager
+
+/**
+ * A helper class which can be used to compare two [ListManager]s.
+ *
+ * @param oldListManager The current [ListManager] to be used in comparison
+ * @param newListManager The new [ListManager] that'll replace the old one
+ * @param areItemsTheSame A compare function to be used to determine if two items refer to the same object. This is
+ * not the function to compare the contents of the items. In most cases, this should compare the ids of two items.
+ * @param areContentsTheSame A compare function to be used to determine if two items has the same contents. This
+ * function will be triggered for items who return true for [areItemsTheSame] and actual content comparison should be
+ * made depending on the view they are used in.
+ */
+class ListManagerDiffCallback<T>(
+    private val oldListManager: ListManager<T>?,
+    private val newListManager: ListManager<T>,
+    private val areItemsTheSame: (T, T) -> Boolean,
+    private val areContentsTheSame: (T, T) -> Boolean
+) : DiffUtil.Callback() {
+    override fun getOldListSize(): Int {
+        return oldListManager?.size ?: 0
+    }
+
+    override fun getNewListSize(): Int {
+        return newListManager.size
+    }
+
+    override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
+        if (oldListManager == null) {
+            return false
+        }
+        return compareItems(oldItemPosition, newItemPosition, areItemsTheSame)
+    }
+
+    override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
+        return compareItems(oldItemPosition, newItemPosition, areContentsTheSame)
+    }
+
+    /**
+     * A helper function to compare two items in the given positions given a compare function.
+     */
+    private fun compareItems(oldItemPosition: Int, newItemPosition: Int, compare: (T, T) -> Boolean): Boolean {
+        // We shouldn't fetch items or load more pages prematurely when we are just trying to compare them
+        val oldItem = oldListManager?.getItem(
+                position = oldItemPosition,
+                shouldFetchIfNull = false,
+                shouldLoadMoreIfNecessary = false
+        )
+        val newItem = newListManager.getItem(
+                position = newItemPosition,
+                shouldFetchIfNull = false,
+                shouldLoadMoreIfNecessary = false
+        )
+        // If two items are null, they are the same for our intends and purposes
+        if (oldItem == null && newItem == null) {
+            return true
+        }
+        // If one of the items is null, but the other one is not, they can't be the same item
+        if (oldItem == null || newItem == null) {
+            return false
+        }
+        return compare(oldItem, newItem)
+    }
+}