fix(connectivity_plus): Ensure Connectivity on Android is correctly r…

…eported when lost (#2836)

packages/connectivity_plus/connectivity_plus/README.md

@@ -58,7 +58,9 @@ if (connectivityResult.contains(ConnectivityResult.mobile)) {
 ```
 
 You can also listen for active connectivity types changes by subscribing to the stream
-exposed by the plugin:
+exposed by the plugin.
+
+This method should ensure emitting only distinct values.
 
 ```dart
 import 'package:connectivity_plus/connectivity_plus.dart';

packages/connectivity_plus/connectivity_plus/android/src/main/java/dev/fluttercommunity/plus/connectivity/Connectivity.java

@@ -8,6 +8,8 @@
 import android.net.Network;
 import android.net.NetworkCapabilities;
 import android.os.Build;
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -27,44 +29,54 @@ public Connectivity(ConnectivityManager connectivityManager) {
   }
 
   List<String> getNetworkTypes() {
-    List<String> types = new ArrayList<>();
     if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
       Network network = connectivityManager.getActiveNetwork();
-      NetworkCapabilities capabilities = connectivityManager.getNetworkCapabilities(network);
-      if (capabilities == null
-          || !capabilities.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)) {
-        types.add(CONNECTIVITY_NONE);
-        return types;
-      }
-      if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_WIFI)
-          || capabilities.hasTransport(NetworkCapabilities.TRANSPORT_WIFI_AWARE)) {
-        types.add(CONNECTIVITY_WIFI);
-      }
-      if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_ETHERNET)) {
-        types.add(CONNECTIVITY_ETHERNET);
-      }
-      if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_VPN)) {
-        types.add(CONNECTIVITY_VPN);
-      }
-      if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_CELLULAR)) {
-        types.add(CONNECTIVITY_MOBILE);
-      }
-      if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_BLUETOOTH)) {
-        types.add(CONNECTIVITY_BLUETOOTH);
-      }
-      if (types.isEmpty()
-          && capabilities.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)) {
-        types.add(CONNECTIVITY_OTHER);
-      }
-      if (types.isEmpty()) {
-        types.add(CONNECTIVITY_NONE);
-      }
+      return getCapabilitiesFromNetwork(network);
     } else {
       // For legacy versions, return a single type as before or adapt similarly if multiple types
       // need to be supported
       return getNetworkTypesLegacy();
     }
+  }
 
+  @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
+  List<String> getCapabilitiesFromNetwork(Network network) {
+    NetworkCapabilities capabilities = connectivityManager.getNetworkCapabilities(network);
+    return getCapabilitiesList(capabilities);
+  }
+
+  @NonNull
+  @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
+  List<String> getCapabilitiesList(NetworkCapabilities capabilities) {
+    List<String> types = new ArrayList<>();
+    if (capabilities == null
+        || !capabilities.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)) {
+      types.add(CONNECTIVITY_NONE);
+      return types;
+    }
+    if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_WIFI)
+        || capabilities.hasTransport(NetworkCapabilities.TRANSPORT_WIFI_AWARE)) {
+      types.add(CONNECTIVITY_WIFI);
+    }
+    if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_ETHERNET)) {
+      types.add(CONNECTIVITY_ETHERNET);
+    }
+    if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_VPN)) {
+      types.add(CONNECTIVITY_VPN);
+    }
+    if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_CELLULAR)) {
+      types.add(CONNECTIVITY_MOBILE);
+    }
+    if (capabilities.hasTransport(NetworkCapabilities.TRANSPORT_BLUETOOTH)) {
+      types.add(CONNECTIVITY_BLUETOOTH);
+    }
+    if (types.isEmpty()
+        && capabilities.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)) {
+      types.add(CONNECTIVITY_OTHER);
+    }
+    if (types.isEmpty()) {
+      types.add(CONNECTIVITY_NONE);
+    }
     return types;
   }
 

packages/connectivity_plus/connectivity_plus/android/src/main/java/dev/fluttercommunity/plus/connectivity/ConnectivityBroadcastReceiver.java

@@ -15,6 +15,7 @@
 import android.os.Handler;
 import android.os.Looper;
 import io.flutter.plugin.common.EventChannel;
+import java.util.List;
 
 /**
  * The ConnectivityBroadcastReceiver receives the connectivity updates and send them to the UIThread
@@ -46,18 +47,31 @@ public void onListen(Object arguments, EventChannel.EventSink events) {
           new ConnectivityManager.NetworkCallback() {
             @Override
             public void onAvailable(Network network) {
-              sendEvent();
+              // onAvailable is called when the phone switches to a new network
+              // e.g. the phone was offline and gets wifi connection
+              // or the phone was on wifi and now switches to mobile.
+              // The plugin sends the current capability connection to the users.
+              sendEvent(connectivity.getCapabilitiesFromNetwork(network));
             }
 
             @Override
             public void onCapabilitiesChanged(
                 Network network, NetworkCapabilities networkCapabilities) {
-              sendEvent();
+              // This callback is called multiple times after a call to onAvailable
+              // this also causes multiple callbacks to the Flutter layer.
+              sendEvent(connectivity.getCapabilitiesList(networkCapabilities));
             }
 
             @Override
             public void onLost(Network network) {
-              sendEvent();
+              // This callback is called when a capability is lost.
+              //
+              // The provided Network object contains information about the
+              // network capability that has been lost, so we cannot use it.
+              //
+              // Instead, post the current network but with a delay long enough
+              // that we avoid a race condition.
+              sendCurrentStatusWithDelay();
             }
           };
       connectivity.getConnectivityManager().registerDefaultNetworkCallback(networkCallback);
@@ -66,7 +80,7 @@ public void onLost(Network network) {
     }
     // Need to emit first event with connectivity types without waiting for first change in system
     // that might happen much later
-    sendEvent();
+    sendEvent(connectivity.getNetworkTypes());
   }
 
   @Override
@@ -92,11 +106,16 @@ public void onReceive(Context context, Intent intent) {
     }
   }
 
-  private void sendEvent() {
+  private void sendEvent(List<String> networkTypes) {
+    Runnable runnable = () -> events.success(networkTypes);
+    // Emit events on main thread
+    mainHandler.post(runnable);
+  }
+
+  private void sendCurrentStatusWithDelay() {
     Runnable runnable = () -> events.success(connectivity.getNetworkTypes());
-    // The dalay is needed because callback methods suffer from race conditions.
-    // More info:
-    // https://developer.android.com/develop/connectivity/network-ops/reading-network-state#listening-events
-    mainHandler.postDelayed(runnable, 100);
+    // Emit events on main thread
+    // 500 milliseconds to avoid race conditions
+    mainHandler.postDelayed(runnable, 500);
   }
 }

packages/connectivity_plus/connectivity_plus/example/lib/main.dart

@@ -86,6 +86,8 @@ class _MyHomePageState extends State<MyHomePage> {
     setState(() {
       _connectionStatus = result;
     });
+    // ignore: avoid_print
+    print('Connectivity changed: $_connectionStatus');
   }
 
   @override

packages/connectivity_plus/connectivity_plus/lib/connectivity_plus.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 
 import 'package:connectivity_plus_platform_interface/connectivity_plus_platform_interface.dart';
+import 'package:collection/collection.dart';
 
 // Export enums from the platform_interface so plugin users can use them directly.
 export 'package:connectivity_plus_platform_interface/connectivity_plus_platform_interface.dart'
@@ -40,16 +41,14 @@ class Connectivity {
   /// status changes, this is a known issue that only affects simulators.
   /// For details see https://github.com/fluttercommunity/plus_plugins/issues/479.
   ///
-  /// On Android, the Stream may emit new values even when
-  /// the [ConnectivityResult] list remains the same.
-  ///
   /// The emitted list is never empty. In case of no connectivity, the list contains
   /// a single element of [ConnectivityResult.none]. Note also that this is the only
   /// case where [ConnectivityResult.none] is present.
   ///
-  /// This method doesn't filter events, nor it ensures distinct values.
+  /// This method applies [Stream.distinct] over the received events to ensure
+  /// only emiting when connectivity changes.
   Stream<List<ConnectivityResult>> get onConnectivityChanged {
-    return _platform.onConnectivityChanged;
+    return _platform.onConnectivityChanged.distinct((a, b) => a.equals(b));
   }
 
   /// Checks the connection status of the device.

packages/connectivity_plus/connectivity_plus/pubspec.yaml

@@ -41,6 +41,7 @@ dependencies:
   web: '>=0.3.0 <=0.6.0'
   meta: ^1.8.0
   nm: ^0.5.0
+  collection: ^1.18.0
 
 dev_dependencies:
   flutter_test: