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) {

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

@@ -0,0 +1,84 @@
+package com.wireguard.android;
+
+import android.content.Context;
+import android.databinding.DataBindingUtil;
+import android.databinding.ObservableArrayMap;
+import android.databinding.ObservableMap;
+import android.databinding.ViewDataBinding;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.BaseAdapter;
+import android.widget.ListAdapter;
+
+import java.lang.ref.WeakReference;
+
+/**
+ * A generic ListAdapter backed by an ObservableMap.
+ */
+
+class ObservableArrayMapAdapter<K, V> extends BaseAdapter implements ListAdapter {
+    private final int layoutId;
+    private final LayoutInflater layoutInflater;
+    private ObservableArrayMap<K, V> map;
+    private final OnMapChangedCallback<K, V> callback = new OnMapChangedCallback<>(this);
+
+    ObservableArrayMapAdapter(Context context, int layoutId, ObservableArrayMap<K, V> map) {
+        this.layoutInflater = LayoutInflater.from(context);
+        this.layoutId = layoutId;
+        setMap(map);
+    }
+
+    @Override
+    public int getCount() {
+        return map != null ? map.size() : 0;
+    }
+
+    @Override
+    public V getItem(int position) {
+        return map != null ? map.get(map.keyAt(position)) : null;
+    }
+
+    @Override
+    public long getItemId(int position) {
+        return position;
+    }
+
+    @Override
+    public View getView(int position, View convertView, ViewGroup parent) {
+        ViewDataBinding binding = DataBindingUtil.getBinding(convertView);
+        if (binding == null)
+            binding = DataBindingUtil.inflate(layoutInflater, layoutId, parent, false);
+        binding.setVariable(BR.item, getItem(position));
+        binding.executePendingBindings();
+        return binding.getRoot();
+    }
+
+    public void setMap(ObservableArrayMap<K, V> newMap) {
+        if (map != null)
+            map.removeOnMapChangedCallback(callback);
+        map = newMap;
+        if (map != null) {
+            map.addOnMapChangedCallback(callback);
+        }
+    }
+
+    private static class OnMapChangedCallback<K, V>
+            extends ObservableMap.OnMapChangedCallback<ObservableMap<K, V>, K, V> {
+
+        private final WeakReference<ObservableArrayMapAdapter<K, V>> weakAdapter;
+
+        private OnMapChangedCallback(ObservableArrayMapAdapter<K, V> adapter) {
+            weakAdapter = new WeakReference<>(adapter);
+        }
+
+        @Override
+        public void onMapChanged(ObservableMap<K, V> sender, K key) {
+            final ObservableArrayMapAdapter<K, V> adapter = weakAdapter.get();
+            if (adapter != null)
+                adapter.notifyDataSetChanged();
+            else
+                sender.removeOnMapChangedCallback(this);
+        }
+    }
+}