segunfamisa · September 26, 2019 09:11 · Sep 26, 2019
diff --git a/AdapterObservableListItem.kt b/AdapterObservableListItem.kt
@@ -0,0 +1,56 @@
+class ObservableListField<T, VH : RecyclerView.ViewHolder>(
+    private val adapter: RecyclerView.Adapter<VH>,
+    private val diffUtilCallbackProducer: ((List<T>, List<T>) -> DiffUtil.Callback)?,
+    initialValue: List<T>
+) : ObservableProperty<List<T>>(initialValue = initialValue) {
+
+    private var result: DiffUtil.DiffResult? = null
+
+    override fun beforeChange(
+        property: KProperty<*>,
+        oldValue: List<T>,
+        newValue: List<T>
+    ): Boolean {
+        val diffUtilCallback = diffUtilCallbackProducer?.invoke(oldValue, newValue) ?: SimpleDiffUtilCallback(
+            oldItems = oldValue,
+            newItems = newValue
+        )
+        result = DiffUtil.calculateDiff(diffUtilCallback)
+        return true
+    }
+
+    override fun afterChange(property: KProperty<*>, oldValue: List<T>, newValue: List<T>) {
+        result?.dispatchUpdatesTo(adapter)
+        super.afterChange(property, oldValue, newValue)
+    }
+
+    /**
+     * Very simple diff util callback
+     */
+    private inner class SimpleDiffUtilCallback<T> constructor(
+        private val oldItems: List<T>,
+        private val newItems: List<T>
+    ) :
+        DiffUtil.Callback() {
+        override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean =
+            oldItems[oldItemPosition] == newItems[newItemPosition]
+
+        override fun getOldListSize(): Int = oldItems.size
+
+        override fun getNewListSize(): Int = newItems.size
+
+        override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean =
+            oldItems[oldItemPosition] == newItems[newItemPosition]
+    }
+}
+
+fun <T, VH : RecyclerView.ViewHolder> RecyclerView.Adapter<VH>.observableList(
+    initialValue: List<T>,
+    diffUtilCallbackProducer: ((List<T>, List<T>) -> DiffUtil.Callback)? = null
+): ObservableProperty<List<T>> {
+    return ObservableListField(
+        adapter = this,
+        diffUtilCallbackProducer = diffUtilCallbackProducer,
+        initialValue = initialValue
+    )
+}