ObservableArrayMapAdapter: Copy ObservableListAdapter

Since the conversion to a sequential list (to implement ListAdapter)
depends on the implementation detail that ObservableArrayMap is backed
by an array, we can't use the ObservableMap interface here.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/src/main/java/com/wireguard/android/BindingAdapters.java

@@ -1,6 +1,7 @@
 package com.wireguard.android;
 
 import android.databinding.BindingAdapter;
+import android.databinding.ObservableArrayMap;
 import android.databinding.ObservableList;
 import android.widget.ListView;
 
@@ -9,6 +10,32 @@ import android.widget.ListView;
  */
 
 public final class BindingAdapters {
+    @BindingAdapter({"items", "layout"})
+    public static <K, V> void arrayMapBinding(ListView view, ObservableArrayMap<K, V> oldMap,
+                                              int oldLayoutId, ObservableArrayMap<K, V> newMap,
+                                              int newLayoutId) {
+        // Remove any existing binding when there is no new map.
+        if (newMap == null) {
+            view.setAdapter(null);
+            return;
+        }
+        // The ListAdapter interface is not generic, so this cannot be checked.
+        @SuppressWarnings("unchecked")
+        ObservableArrayMapAdapter<K, V> adapter =
+                (ObservableArrayMapAdapter<K, V>) view.getAdapter();
+        // If the layout changes, any existing adapter must be replaced.
+        if (newLayoutId != oldLayoutId)
+            adapter = null;
+        // Add a new binding if there was none, or if it must be replaced due to a layout change.
+        if (adapter == null) {
+            adapter = new ObservableArrayMapAdapter<>(view.getContext(), newLayoutId, newMap);
+            view.setAdapter(adapter);
+        } else if (newMap != oldMap) {
+            // Changing the list only requires modifying the existing adapter.
+            adapter.setMap(newMap);
+        }
+    }
+
     @BindingAdapter({"items", "layout"})
     public static <T> void listBinding(ListView view, ObservableList<T> oldList, int oldLayoutId,
                                        ObservableList<T> newList, int newLayoutId) {