binding: Weakly reference adapter in list change callback

This allows the ObservableListAdapter to be garbage collected along with
its activity. On the next list change, the OnListChangedCallback will
detect that the adapter is gone and clean itself up. This avoids needing
to manually remove the list from the adapter, as would otherwise be
required to break the reference cycle adapter→list→listener→adapter.

This will be relevant once the list of profiles outlives the activity.

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

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

@@ -10,6 +10,8 @@ import android.view.ViewGroup;
 import android.widget.BaseAdapter;
 import android.widget.ListAdapter;
 
+import java.lang.ref.WeakReference;
+
 /**
  * A generic ListAdapter backed by an ObservableList.
  */
@@ -18,7 +20,7 @@ class ObservableListAdapter<T> extends BaseAdapter implements ListAdapter {
     private final int layoutId;
     private final LayoutInflater layoutInflater;
     private ObservableList<T> list;
-    private final OnListChangedCallback<ObservableList<T>> callback = new OnListChangedCallback<>();
+    private final OnListChangedCallback<T> callback = new OnListChangedCallback<>(this);
 
     ObservableListAdapter(Context context, int layoutId, ObservableList<T> list) {
         this.layoutInflater = LayoutInflater.from(context);
@@ -60,32 +62,44 @@ class ObservableListAdapter<T> extends BaseAdapter implements ListAdapter {
         }
     }
 
-    private class OnListChangedCallback<L extends ObservableList<T>>
-            extends ObservableList.OnListChangedCallback<L> {
+    private static class OnListChangedCallback<U>
+            extends ObservableList.OnListChangedCallback<ObservableList<U>> {
+
+        private final WeakReference<ObservableListAdapter<U>> weakAdapter;
+
+        private OnListChangedCallback(ObservableListAdapter<U> adapter) {
+            weakAdapter = new WeakReference<>(adapter);
+        }
+
         @Override
-        public void onChanged(L sender) {
-            ObservableListAdapter.this.notifyDataSetChanged();
+        public void onChanged(ObservableList<U> sender) {
+            final ObservableListAdapter<U> adapter = weakAdapter.get();
+            if (adapter != null)
+                adapter.notifyDataSetChanged();
+            else
+                sender.removeOnListChangedCallback(this);
         }
 
         @Override
-        public void onItemRangeChanged(L sender, int positionStart, int itemCount) {
-            ObservableListAdapter.this.notifyDataSetChanged();
+        public void onItemRangeChanged(ObservableList<U> sender, int positionStart, int itemCount) {
+            onChanged(sender);
         }
 
         @Override
-        public void onItemRangeInserted(L sender, int positionStart, int itemCount) {
-            ObservableListAdapter.this.notifyDataSetChanged();
+        public void onItemRangeInserted(ObservableList<U> sender, int positionStart,
+                                        int itemCount) {
+            onChanged(sender);
         }
 
         @Override
-        public void onItemRangeMoved(L sender, int fromPosition, int toPosition,
+        public void onItemRangeMoved(ObservableList<U> sender, int fromPosition, int toPosition,
                                      int itemCount) {
-            ObservableListAdapter.this.notifyDataSetChanged();
+            onChanged(sender);
         }
 
         @Override
-        public void onItemRangeRemoved(L sender, int positionStart, int itemCount) {
-            ObservableListAdapter.this.notifyDataSetChanged();
+        public void onItemRangeRemoved(ObservableList<U> sender, int positionStart, int itemCount) {
+            onChanged(sender);
         }
     }
 }