Develop Reference

Xamarin Forms - How to check setting of RequestIgnoreBatteryOptimizations permission on Android

(See UPDATE below)
I have a Xamarin Forms app on Android which uses the Xamarin.Essentials library.
The app requires to run in the background to be fed location data (not particularly relevant to the question in hand, but included for context), and so must not be put to sleep by any battery optimisations that the OS might attempt.
I know that the user can manually opt out specific apps from Battery Optimizations, but as it is so crucial to the successful operation of the app, I would like the app to be able to :
check the Battery Optimization Opt-out permission status to ensure it is appropriately set,
and/or
force Android to opt the app of any battery optimizations.
I have added an entry into AndroidManifest.xml, but it doesn't seem to help, with the newly-installed app defaulting to being Battery Optimized.
AndroidManifest.xml
The manifest contains the following entry:
<uses-permission android:name="android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS" />
Xamarin.Essentials
This library gives access to a number of permission-related info on the device, but Battery Optimizations doesn't seem to be one of them.
Device being used
I don't know if it's relevant, but I am testing on a Samsung Galaxy S20 Ultra.
Can anyone offer any advice?
UPDATE Aug 28 2021
Following the advice from contributors and with reference to the docs at https://learn.microsoft.com/en-us/xamarin/essentials/permissions?tabs=android#extending-permissions ...
In My Shared Code
public interface IRequestIgnoreBatteryOptimizationPermission
{
Task<PermissionStatus> CheckStatusAsync();
Task<PermissionStatus> RequestAsync();
}
In My Android Project
[assembly: Xamarin.Forms.Dependency(typeof(RequestIgnoreBatteryOptimizationPermission))]
namespace MyAndroidProject
{
public class RequestIgnoreBatteryOptimizationPermission : Permissions.BasePlatformPermission, IRequestIgnoreBatteryOptimizationPermission
{
public override (string androidPermission, bool isRuntime)[] RequiredPermissions => new List<(string androidPermission, bool isRuntime)>
{
(Android.Manifest.Permission.RequestIgnoreBatteryOptimizations, true)
}.ToArray();
}
}
On Shared App Initialization
// Ensure Required Permissions have been granted
var requestIgnoreBatteryOptimizationPermission = DependencyService.Get<IRequestIgnoreBatteryOptimizationPermission>();
var status = requestIgnoreBatteryOptimizationPermission.CheckStatusAsync().Result;
if (status != PermissionStatus.Granted)
{
status = requestIgnoreBatteryOptimizationPermission.RequestAsync().Result;
}
Result...
On calling CheckStatusAsync, the result comes back as Granted.
But the app settings still say otherwise...
I've tried it on both a physical device (Samsung Galaxy S20 Ultra) and on an Android Emulator (Pixel 2 API 28), with same result on both.

From this document, there are two ways to set Battery Optimization
An app can fire the ACTION_IGNORE_BATTERY_OPTIMIZATION_SETTINGS intent to take the user directly to the Battery Optimization, where they can add the app.
An app holding the REQUEST_IGNORE_BATTERY_OPTIMIZATIONS permission can trigger a system dialog to let the user add the app to the exemption list directly, without going to settings. The app fires a ACTION_REQUEST_IGNORE_BATTERY_OPTIMIZATIONS Intent to trigger the dialog.
I use PowserManager.isIgnoringBatteryOptimizations to check Battery Optimization.
Firstly, add RequestIgnoreBatteryOptimizations in AndroidManifest.xml
<uses-permission android:name="android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS" />
Then creating Interface in Shared code.
public interface IBattery
{
void getbattery();
}
Implementing this interface in Android platform.
[assembly: Dependency(typeof(ImplementBattery))]
namespace FormsSample.Droid
{
public class ImplementBattery : IBattery
{
public void getbattery()
{
Intent intent = new Intent();
String packageName = MainActivity.mac.PackageName;
PowerManager pm = (PowerManager)MainActivity.mac.GetSystemService(Context.PowerService);
if (pm.IsIgnoringBatteryOptimizations(packageName))
intent.SetAction(Android.Provider.Settings.ActionIgnoreBatteryOptimizationSettings);
else
{
intent.SetAction(Android.Provider.Settings.ActionRequestIgnoreBatteryOptimizations);
intent.SetData(Android.Net.Uri.Parse("package:" + packageName));
}
MainActivity.mac.StartActivity(intent);
}
}
}
Creating static Mainactivity field in Mainactivity.cs.
public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
public static MainActivity mac;
protected override void OnCreate(Bundle savedInstanceState)
{
initFontScale();
TabLayoutResource = Resource.Layout.Tabbar;
ToolbarResource = Resource.Layout.Toolbar;
base.OnCreate(savedInstanceState);
mac = this;
Now, using DependencyService to fire.
private void Button_Clicked(object sender, EventArgs e)
{
DependencyService.Get<IBattery>().getbattery();
}

In your MainActivity add two properties:
private const int RequestPermissionsId = 0
and
private readonly string[] ManifestPermissions =
{
Manifest.Permission.RequestIgnoreBatteryOptimizations
// Add here other permissions you want to check
}
Then override the OnStart method and force permission check there:
public override void OnStart()
{
base.OnStart();
if ((int)Build.VERSION.SdkInt >= 23)
{
if (CheckSelfPermission(Manifest.Permission.RequestIgnoreBatteryOptimizations != Permission.Granted)
RequestPermissions(ManifestPermissions, RequestPermissionsId);
}
}
And of course, remember that you must have the OnRequestPermissionsResult method implemented:
public override void OnRequestPermissionsResult(int requestCode, string[] permissions, Permission[] grantResults)
{
Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);
base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
}

Well, I am guessing you are trying to check it directly through shared code
The easiest way to do it would be to extend the needed permission in native using essentials.
Check the status and request permission through an interface:
public interface IRequestIgnoreBatteryOptimizations
{
Task<PermissionStatus> CheckStatusAsync();
Task<PermissionStatus> RequestAsync();
}
Implement the native part for the same:
public class IgnoreBatteryOptimizationsPlatformPermission : Xamarin.Essentials.Permissions.BasePlatformPermission, IRequestIgnoreBatteryOptimizations
{
public override (string androidPermission, bool isRuntime)[] RequiredPermissions =>
new (string, bool)[] { (Manifest.Permission.RequestIgnoreBatteryOptimizations, true) };
}
Then register it in your Native XF caller class(MainActivity, Appdelegate(for some other permission))
DependencyService.Register<IRequestIgnoreBatteryOptimizations, IgnoreBatteryOptimizationsPlatformPermission>();
And then in your XF class use this method:
public static async Task<PermissionStatus> CheckAndRequestBatteryOptimizations()
{
var batteryOptimizationsPermission = DependencyService.Get<IRequestIgnoreBatteryOptimizations>();
var status = await batteryOptimizationsPermission.CheckStatusAsync();
if (status != PermissionStatus.Granted)
{
status = await batteryOptimizationsPermission.RequestAsync();
}
return status;
}
And then request for it whenever you like:
var status= await CheckAndRequestBatteryOptimizations();
More information here: https://learn.microsoft.com/en-us/xamarin/essentials/permissions?tabs=android#extending-permissions

Scan and listen to events from Bluetooth devices in background with flutter

I want to set up a mobile application with flutter which also runs in the background. this application allows you to scan Bluetooth devices and listen to events to launch notification and/or start a ringtone.
I managed to do all this and it works very well with the flutter_blue plugin. But my problem is that the application has to keep running in the background.
I came here to seek help.
The app does exactly what this app does https://play.google.com/store/apps/details?id=com.antilost.app3&hl=fr&gl=US

There are 2 ways to do it.
All you have to do that is write a native code in JAVA/Kotlin for android and obc-c/swift for ios.
The best place to start with this is here
If you just follow the above link then you will be able to code MethodChannel and EventChannel, which will be useful to communicate between flutter and native code. So, If you are good at the native side then it won't be big deal for you.
// For example, if you want to start service in android
// we write
//rest of the activity code
onCreate(){
startBluetoothService();
}
startBluetoothService(){
//your code
}
//then, For the flutter
// Flutter side
MessageChannel msgChannel=MessageChannel("MyChannel");
msgChannel.invokeMethode("startBluetoothService");
// Native side
public class MainActivity extends FlutterActivity {
private static final String CHANNEL = "MyChannel";
#Override
public void configureFlutterEngine(#NonNull FlutterEngine flutterEngine) {
super.configureFlutterEngine(flutterEngine);
new MethodChannel(flutterEngine.getDartExecutor().getBinaryMessenger(), CHANNEL)
.setMethodCallHandler(
(call, result) -> {
if (call.method.equals("startBluetoothService")) {
int response = startBluetoothService();
//then you can return the result based on the your code execution
if (response != -1) {
result.success(response);
} else {
result.error("UNAVAILABLE", "Error while starting service.", null);
}
} else {
result.notImplemented();
}
}
);
}
}
same as above you can write the code for the iOS side.
Second way is to write your own plugin for that you can take inspiration from alarm_manager or Background_location plugins.
I hope it helps you to solve the problem.

Run flutter code when android application class starts

I'm making a plugin for Flutter to handle fcm messages using an android native library.
As we know when a message is received by FCM, it starts the app (It's application class) and runs the codes within Application#onCreate block, so we can run native code when app starts by fcm in the background.
My question is, is it possible to run flutter code at that time when application starts?
For instance if the message was received:
Application class:
public class Application extends FlutterApplication {
#Override
public void onCreate() {
super.onCreate();
// Start flutter engine
// Invoke a dart code in the Plugin using methodChannel or etc.
}
}

Short answer, Yes
You can call a Dart method in background using it's handle key.
1. Register your plugin in the background
Implement a custom application class (override FlutterApplication)
public class MyApp extends FlutterApplication implements PluginRegistry.PluginRegistrantCallback {
#Override
public void registerWith(io.flutter.plugin.common.PluginRegistry registry) {
// For apps using FlutterEmbedding v1
GeneratedPluginRegistrant.registerWith(registry);
// App with V2 will initialize plugins automatically, you might need to register your own however
}
}
Remember to register the class in the AndroidManifest by adding android:name=".MyApp" to <application> attributes.
What is embedding v2?
2. Create a setup function as top level function in your flutter code
/// Define this TopLevel or static
void _setup() async {
MethodChannel backgroundChannel = const MethodChannel('flutter_background');
// Setup Flutter state needed for MethodChannels.
WidgetsFlutterBinding.ensureInitialized();
// This is where the magic happens and we handle background events from the
// native portion of the plugin.
backgroundChannel.setMethodCallHandler((MethodCall call) async {
if (call.method == 'handleBackgroundMessage') {
final CallbackHandle handle =
CallbackHandle.fromRawHandle(call.arguments['handle']);
final Function handlerFunction =
PluginUtilities.getCallbackFromHandle(handle);
try {
var dataArg = call.arguments['message'];
if (dataArg == null) {
print('Data received from callback is null');
return;
}
await handlerFunction(dataArg);
} catch (e) {
print('Unable to handle incoming background message.\n$e');
}
}
return Future.value();
});
3. Create a top level callback that will get the background message and calls it
_bgFunction(dynamic message) {
// Message received in background
// Remember, this will be a different isolate. So, no widgets
}
4. Get the handle key of the background function and setup and send it to native via MethodChannel
// dart:ui needed
CallbackHandle setup PluginUtilities.getCallbackHandle(_setup);
CallbackHandle handle PluginUtilities.getCallbackHandle(_bgFunction);
_channel.invokeMethod<bool>(
'handleFunction',
<String, dynamic>{
'handle': handle.toRawHandle(),
'setup': setup.toRawHandle()
},
);
5. Save them into SharedPref in the native side
public void onMethodCall(MethodCall call, MethodChannel.Result result) {
String methodName = call.method
if (methodName == "handleFunction") {
long handle = call.argument("handle");
long setup = call.argument("setup");
// save them
}
}
6. When background is awaken, start a background isolate
FlutterMain.ensureInitializationComplete(context, null)
val appBundlePath = FlutterMain.findAppBundlePath()
val flutterCallback = FlutterCallbackInformation.lookupCallbackInformation(setupHandleYouHadSaved)
FlutterNativeView backgroundFlutterView = FlutterNativeView(context, true)
val args = FlutterRunArguments()
args.bundlePath = appBundlePath
args.entrypoint = flutterCallback.callbackName
args.libraryPath = flutterCallback.callbackLibraryPath
backgroundFlutterView?.runFromBundle(args)
// Initialize your registrant in the app class
pluginRegistrantCallback?.registerWith(backgroundFlutterView?.pluginRegistry)
7. When your plugin is registered, create a background channel and pass it to
val backgroundChannel = MethodChannel(messenger, "pushe_flutter_background")
8. Call the setup method that would call and give the message to you callback
private fun sendBackgroundMessageToExecute(context: Context, message: String) {
if (backgroundChannel == null) {
return
}
val args: MutableMap<String, Any?> = HashMap()
if (backgroundMessageHandle == null) {
backgroundMessageHandle = getMessageHandle(context)
}
args["handle"] = backgroundMessageHandle
args["message"] = message
// The created background channel at step 7
backgroundChannel?.invokeMethod("handleBackgroundMessage", args, null)
}
The sendBackgroundMessageToExecute will execute the dart _setup function and pass the message and callback handle. In the step 2, callback will be called.
Note: There are still certain corner cases you may want to consider (for instance thread waiting and ...). Checkout the samples and see the source code.
There are several projects which support background execution when app is started in the background.
FirebaseMessaging
Pushe
WorkManager

I did it a different, simpler way compared to Mahdi's answer. I avoided defining an additional entrypoint/ callback, using PluginUtilities, callback handles, saving handles in SharedPreferences, passing messages with handles between dart and platform, or implementing a FlutterApplication.
I was working on a flutter plugin (so you don't have to worry about this if you use my library for push notifications 😂), so I implement FlutterPlugin. If I want to do background processing and the Flutter app isn't running, I just launch the Flutter app without an Activity or View. This is only necessary on Android, since the FlutterEngine/ main dart function runs already runs when a background message is received in an iOS app. The benefit is that this is the same behaviour as iOS: a Flutter app is always running when the app is launched, even if there is no app shown to the user.
I launch the application by using:
flutterEngine = new FlutterEngine(context, null);
DartExecutor executor = flutterEngine.getDartExecutor();
backgroundMethodChannel = new MethodChannel(executor, "com.example.package.background");
backgroundMethodChannel.setMethodCallHandler(this);
// Get and launch the users app isolate manually:
executor.executeDartEntrypoint(DartExecutor.DartEntrypoint.createDefault());
I did this to implement background push notification handling in a library, ably_flutter. It seems to work well. The FlutterEngine/ application is launched only when the application is not already running. I do this by keeping track of the activity (using ActivityAware):
if (isApplicationInForeground) {
// Send message to Dart side app already running
Intent onMessageReceivedIntent = new Intent(PUSH_ON_MESSAGE_RECEIVED);
onMessageReceivedIntent.putExtras(intent.getExtras());
LocalBroadcastManager.getInstance(context).sendBroadcast(onMessageReceivedIntent);
} else if (AblyFlutterPlugin.isActivityRunning) {
// Flutter is already running, just send a background message to it.
Intent onMessageReceivedIntent = new Intent(PUSH_ON_BACKGROUND_MESSAGE_RECEIVED);
onMessageReceivedIntent.putExtras(intent.getExtras());
LocalBroadcastManager.getInstance(context).sendBroadcast(onMessageReceivedIntent);
} else {
// No existing Flutter Activity is running, create a FlutterEngine and pass it the RemoteMessage
new PushBackgroundIsolateRunner(context, asyncCompletionHandlerPendingResult, message);
}
Then, I just use a separate MethodChannel to pass the messages back to the dart side. There's more to this parallel processing (like telling the Java side that the App is running/ ready. Search for call.method.equals(pushSetOnBackgroundMessage) in the codebase.). You can see more about the implementation PushBackgroundIsolateRunner.java at ably_flutter. I also used goAsync inside the broadcast receiver to extend the execution time from 10s to 30s, to be consistent with iOS 30s wall clock time.

You can use a headless Runner to run dart code from an Application class (or service, broadcast receiver etc).
There's a good in depth article on how to implement this: https://medium.com/flutter/executing-dart-in-the-background-with-flutter-plugins-and-geofencing-2b3e40a1a124

According to my knowledge we have to call a class GeneratedPluginRegistrant.registerWith(this); at oncreate method where flutter code has to run.

If you mean you want to run some arbitrary Dart code in the background you can use the this plugin we created which really facilitates the use of background work.
You can register a background job that should be executed at a given point in time and it will call back in to your Dart code where you can run some code in the background.
//Provide a top level function or static function.
//This function will be called by Android and will return the value you provided when you registered the task.
//See below
void callbackDispatcher() {
Workmanager.defaultCallbackDispatcher((echoValue) {
print("Native echoed: $echoValue");
return Future.value(true);
});
}
Workmanager.initialize(callbackDispatcher)
Then you can schedule them.
Workmanager.registerOneOffTask(
"1",
"simpleTask"
);
The String simpleTask will be returned in the callbackDispatcher function once it starts running in the background.
This allows for you to schedule multiple background jobs and identify them by this id.

Push Notification use payload to open correct page

First off I am using Xamarin Forms for a WP8, iOS and Android app.
Goal:
I want to go to a specific page when the toast is clicked depending
upon the payload information of the toast notification.
I have push notifications using Azure Notification Hubs all setup and working well. I use MVVMLight and their dependency injection to setup push notifications specifically for each platform.
Each payload needs to be sent a little different due to the different formats required. With each you will notice I want to send a SignalId in the payload to perform a different action as required on the receiving device from regular push notifications.
Android
{
"data" : {
"msg" : "message in here",
"signalId" : "id-in-here",
},
}
iOS
{
"aps" : { "alert" : "message in here" },
"signalId" : "id-in-here"
}
Windows Phone 8
<?xml version="1.0" encoding="utf-8"?>
<wp:Notification xmlns:wp="WPNotification">
<wp:Toast>
<wp:Text1>category</wp:Text1>
<wp:Text2>message in here</wp:Text2>
<wp:Param>?signalId=id-in-here</wp:Param>
</wp:Toast>
</wp:Notification>
.
Question:
How do I get this information in a Xamarin Forms app and redirect to
the appropriate page when the application is reactivated because the
user clicked on the toast notification?
I want to get the payload information when the app loads, then say, yes this contains a SignalId, lets redirect to this page.
At the moment all it does it show the application when a toast notification is clicked. Must I do it specific to the app, or is there a Xamarin Forms way?
Any help appreciated even if you only know how to do it for one platform, I can probably work my way around the other platforms from there.

I have found the way to do it for all platforms. Windows has been tested, Android and iOS haven't.
Windows and iOS work on a show toast notification if the app is in the background, or let your code deal with it if the app is in the foreground. Android shows the toast regardless of application status.
With Windows Phone 8 I need to go to the MainPage.xaml.cs and add in this override.
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
base.OnNavigatedTo(e);
if (this.NavigationContext.QueryString.ContainsKey("signalId"))
{
var signalId = this.NavigationContext.QueryString["signalId"];
var id = Guid.Empty;
if (signalId != null
&& Guid.TryParse(signalId, out id)
&& id != Guid.Empty)
{
this.NavigationContext.QueryString.Clear();
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
// Do my navigation to a new page
});
}
}
}
For Android in the GcmService
protected override void OnMessage(Context context, Intent intent)
{
Log.Info(Tag, "GCM Message Received!");
var message = intent.Extras.Get("msg").ToString();
var signalId = Guid.Empty;
if (intent.Extras.ContainsKey("signalId"))
{
signalId = new Guid(intent.Extras.Get("signalId").ToString());
}
// Show notification as usual
CreateNotification("", message, signalId);
}
Then in the CreateNotification function put some extra information in the Intent.
var uiIntent = new Intent(this, typeof(MainActivity));
if (signalId != Guid.Empty)
{
uiIntent.PutExtra("SignalId", signalId.ToString());
}
Then in the MainActivity.cs override this function
protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
if (data.HasExtra("SignalId"))
{
Guid signalId = new Guid(data.GetStringExtra("SignalId"));
if (signalId != Guid.Empty)
{
data.RemoveExtra("SignalId");
// Do you navigation
}
}
}
In iOS you will notice I have enhanced the default ProcessNotification()
void ProcessNotification(NSDictionary options, bool fromFinishedLaunching)
{
// Check to see if the dictionary has the aps key. This is the notification payload you would have sent
if (null != options && options.ContainsKey(new NSString("aps")))
{
//Get the aps dictionary
var aps = options.ObjectForKey(new NSString("aps")) as NSDictionary;
var alert = string.Empty;
//Extract the alert text
// NOTE: If you're using the simple alert by just specifying
// " aps:{alert:"alert msg here"} " this will work fine.
// But if you're using a complex alert with Localization keys, etc.,
// your "alert" object from the aps dictionary will be another NSDictionary.
// Basically the json gets dumped right into a NSDictionary,
// so keep that in mind.
if (aps.ContainsKey(new NSString("alert")))
alert = ((NSString) aps[new NSString("alert")]).ToString();
// If this came from the ReceivedRemoteNotification while the app was running,
// we of course need to manually process things like the sound, badge, and alert.
if (!fromFinishedLaunching)
{
//Manually show an alert
if (!string.IsNullOrEmpty(alert))
{
var signalId = new Guid(options.ObjectForKey(new NSString("signalId")) as NSString);
// Show my own toast with the signalId
}
}
}
}
Then in the FinishedLaunching function check if there is any payload
// Check if any payload from the push notification
if (options.ContainsKey("signalId"))
{
var signalId = new Guid(options.ObjectForKey(new NSString("signalId")) as NSString);
// Do the navigation here
}

Pebble Communication Issues [AppSync/AppMessage]

I'm currently attempting to use AppSync to sync a piece of data between an android app and a pebble app. However, I seem to not be able to get the pebble to realize that any data is being transferred - that is, no logs are being produced where they should be. What is really bothering me is that this is essentially the code found in the pebble weather example. I've pasted the relevant bits of code below - could someone possibly look it over and suggest where any issues may be? I've made sure that the UUIDs in both programs (pebble app and android app) are the same, and that they are on the same network, and that the pebble is actually connected to the phone, and that the android function is actually being called and all.
Snippet of pebble app code:
static void sync_error_callback(DictionaryResult dict_error, AppMessageResult app_message_error, void *context) {
APP_LOG(APP_LOG_LEVEL_DEBUG, "App Message Sync Error: %d", app_message_error);
}
static void sync_tuple_changed_callback(const uint32_t key, const Tuple* new_tuple, const Tuple* old_tuple, void* context) {
APP_LOG(APP_LOG_LEVEL_DEBUG, new_tuple->value->cstring);
}
void home_screen_load() {
// set up each one of the SimpleMenuItems
Tuplet initial_values[] = {
TupletCString(0x0, "Initial 1")
};
app_sync_init(&sync, sync_buffer, sizeof(sync_buffer), initial_values, ARRAY_LENGTH(initial_values), sync_tuple_changed_callback, sync_error_callback, NULL);
}
Snippet of android app:
final UUID PEBBLE_APP_UUID = UUID.fromString("10549fd4-1fe4-4d30-8a18-6f2f8149f8fd");
public void sendDataToWatch(String toSend) {
// Build up a Pebble dictionary containing the weather icon and the current temperature in degrees celsius
PebbleDictionary data = new PebbleDictionary();
data.addString(0x0, toSend);
PebbleKit.sendDataToPebble(getApplicationContext(), PEBBLE_APP_UUID, data);
}

To debug this type of problem, you should set a inbox_dropped handler and see if you get anything there.
After initializing AppMessage and AppSync, call:
app_message_register_inbox_dropped(appmsg_in_dropped);
And add this function:
static void appmsg_in_dropped(AppMessageResult reason, void *context) {
APP_LOG(APP_LOG_LEVEL_DEBUG, "In dropped: %s", translate_error(reason));
}
Take a look at this question for the source of the translate_error function.