1 files changed, 99 insertions, 0 deletions
diff --git a/ui/src/main/java/com/wireguard/android/activity/BaseActivity.java b/ui/src/main/java/com/wireguard/android/activity/BaseActivity.java
new file mode 100644
index 00000000..8ec58ee8
--- /dev/null
+++ b/ui/src/main/java/com/wireguard/android/activity/BaseActivity.java
@@ -0,0 +1,99 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.activity;
+
+import androidx.databinding.CallbackRegistry;
+import androidx.databinding.CallbackRegistry.NotifierCallback;
+import android.os.Bundle;
+import androidx.annotation.Nullable;
+
+import com.wireguard.android.Application;
+import com.wireguard.android.model.ObservableTunnel;
+
+import java.util.Objects;
+
+/**
+ * Base class for activities that need to remember the currently-selected tunnel.
+ */
+
+public abstract class BaseActivity extends ThemeChangeAwareActivity {
+    private static final String KEY_SELECTED_TUNNEL = "selected_tunnel";
+
+    private final SelectionChangeRegistry selectionChangeRegistry = new SelectionChangeRegistry();
+    @Nullable private ObservableTunnel selectedTunnel;
+
+    public void addOnSelectedTunnelChangedListener(final OnSelectedTunnelChangedListener listener) {
+        selectionChangeRegistry.add(listener);
+    }
+
+    @Nullable
+    public ObservableTunnel getSelectedTunnel() {
+        return selectedTunnel;
+    }
+
+    @Override
+    protected void onCreate(@Nullable final Bundle savedInstanceState) {
+        // Restore the saved tunnel if there is one; otherwise grab it from the arguments.
+        final String savedTunnelName;
+        if (savedInstanceState != null)
+            savedTunnelName = savedInstanceState.getString(KEY_SELECTED_TUNNEL);
+        else if (getIntent() != null)
+            savedTunnelName = getIntent().getStringExtra(KEY_SELECTED_TUNNEL);
+        else
+            savedTunnelName = null;
+
+        if (savedTunnelName != null)
+            Application.getTunnelManager().getTunnels()
+                    .thenAccept(tunnels -> setSelectedTunnel(tunnels.get(savedTunnelName)));
+
+        // The selected tunnel must be set before the superclass method recreates fragments.
+        super.onCreate(savedInstanceState);
+    }
+
+    @Override
+    protected void onSaveInstanceState(final Bundle outState) {
+        if (selectedTunnel != null)
+            outState.putString(KEY_SELECTED_TUNNEL, selectedTunnel.getName());
+        super.onSaveInstanceState(outState);
+    }
+
+    protected abstract void onSelectedTunnelChanged(@Nullable ObservableTunnel oldTunnel, @Nullable ObservableTunnel newTunnel);
+
+    public void removeOnSelectedTunnelChangedListener(
+            final OnSelectedTunnelChangedListener listener) {
+        selectionChangeRegistry.remove(listener);
+    }
+
+    public void setSelectedTunnel(@Nullable final ObservableTunnel tunnel) {
+        final ObservableTunnel oldTunnel = selectedTunnel;
+        if (Objects.equals(oldTunnel, tunnel))
+            return;
+        selectedTunnel = tunnel;
+        onSelectedTunnelChanged(oldTunnel, tunnel);
+        selectionChangeRegistry.notifyCallbacks(oldTunnel, 0, tunnel);
+    }
+
+    public interface OnSelectedTunnelChangedListener {
+        void onSelectedTunnelChanged(@Nullable ObservableTunnel oldTunnel, @Nullable ObservableTunnel newTunnel);
+    }
+
+    private static final class SelectionChangeNotifier
+            extends NotifierCallback<OnSelectedTunnelChangedListener, ObservableTunnel, ObservableTunnel> {
+        @Override
+        public void onNotifyCallback(final OnSelectedTunnelChangedListener listener,
+                                     final ObservableTunnel oldTunnel, final int ignored,
+                                     final ObservableTunnel newTunnel) {
+            listener.onSelectedTunnelChanged(oldTunnel, newTunnel);
+        }
+    }
+
+    private static final class SelectionChangeRegistry
+            extends CallbackRegistry<OnSelectedTunnelChangedListener, ObservableTunnel, ObservableTunnel> {
+        private SelectionChangeRegistry() {
+            super(new SelectionChangeNotifier());
+        }
+    }
+}