Develop Reference

Xamarin.Forms Firebasepushnotification plugin OnNotificationOpened event causes app to restart for android

I'm trying to handle a notifications opening on android that I've sent through Google's FCM on the SharedProject level by using "Plugin.FirebasePushNotification" plugin and subscribing to "OnNotificationOpened" event.
When I try to open the notification while the app is in the background I'm able to hit a breakpoint inside "OnNotificationOpened" event but after the work inside the event ends the App const. is hit and the application restarts.
I want the application to continue from its last state and hit "OnResume" method that is located inside the App class.
I've done some research about it online and almost all of them were about how splash activity might cause this issue so I've disabled my splash activity by turning the whole "SplashActivity.cs" file into a comment except the namespace and usages and implemented the wanted features of splashactivity(style) inside the "MainActivity" class after that I made sure my "MainActivity" class was the only activity that had it's "MainLauncher" attribute set to true but the problem continues.
Here are the relevant classes:
FirebaseReg.cs
public class FirebaseReg
{
public static void FirebaseInit()
{
CrossFirebasePushNotification.Current.OnTokenRefresh += (s, p) =>
{
System.Diagnostics.Debug.WriteLine($"TOKEN : {p.Token}");
CrossFirebasePushNotification.Current.Subscribe("defaultTopic");
};
CrossFirebasePushNotification.Current.OnNotificationOpened += (s, p) =>
{
try
{
//Breakpoint hits here and I'm able to finish all my work without any exceptions
}
catch (Exception ex)
{
}
};
CrossFirebasePushNotification.Current.OnNotificationAction += (s, p) =>
{
};
CrossFirebasePushNotification.Current.OnNotificationReceived += Current_OnNotificationReceived;
}
private static void Current_OnNotificationReceived(object source, FirebasePushNotificationDataEventArgs e)
{
//DO WORK
}
}
App.xaml.cs
public partial class App : Application
{
public static Uri ServerUri = new Uri(" ");
public static bool IsInForeground { get; set; } = false;
public App()
{
try
{
InitializeComponent(); //After the work in OnNotificationOpened ends breakpoint goes here
Application.Current.UserAppTheme = OSAppTheme.Unspecified;
Application.Current.MainPage = new LoginPage();
}
catch (Exception ex)
{
}
}
protected override void OnStart()
{
IsInForeground = true;
}
protected override void OnSleep()
{
IsInForeground = false;
}
protected override void OnResume()
{
IsInForeground = true;
}
}
MainActivity.cs
[Activity(Label = "TestProject1", Theme = "#style/MyTheme.Splash", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize )]
public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
protected override void OnCreate(Bundle savedInstanceState)
{
base.Window.RequestFeature(WindowFeatures.ActionBar);
// Name of the MainActivity theme you had there before.
// Or you can use global::Android.Resource.Style.ThemeHoloLight
base.SetTheme(Resource.Style.MainTheme);
base.OnCreate(savedInstanceState);
Rg.Plugins.Popup.Popup.Init(this);
UserDialogs.Init(this);
Xamarin.FormsGoogleMaps.Init(this, savedInstanceState);
Xamarin.Essentials.Platform.Init(this, savedInstanceState);
global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
FirebasePushNotificationManager.ProcessIntent(this ,Intent);
LoadApplication(new App());
}
protected override void OnNewIntent(Intent intent)
{
FirebasePushNotificationManager.ProcessIntent(this, intent);
base.OnNewIntent(intent);
}
public override void OnRequestPermissionsResult(int requestCode, string[] permissions, Permission[] grantResults)
{
Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);
base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
}
}
MainApplication.cs
[Application]
public class MainApplication : Application, Application.IActivityLifecycleCallbacks
{
public MainApplication(IntPtr handle, JniHandleOwnership transer) : base(handle, transer)
{
}
public override void OnCreate()
{
base.OnCreate();
RegisterActivityLifecycleCallbacks(this);
if (Build.VERSION.SdkInt >= Android.OS.BuildVersionCodes.O)
{
FirebasePushNotificationManager.DefaultNotificationChannelId = "DefaultChannel";
FirebasePushNotificationManager.DefaultNotificationChannelName = "defaultTopic";
}
#if DEBUG
FirebasePushNotificationManager.Initialize(this, true);
FirebaseRegister.FirebaseInit();
#else
FirebasePushNotificationManager.Initialize(this, false);
FirebaseRegister.FirebaseInit();
#endif
}
public override void OnTerminate()
{
base.OnTerminate();
UnregisterActivityLifecycleCallbacks(this);
}
public void OnActivityCreated(Activity activity, Bundle savedInstanceState)
{
CrossCurrentActivity.Current.Activity = activity;
}
public void OnActivityDestroyed(Activity activity)
{
}
public void OnActivityPaused(Activity activity)
{
}
public void OnActivityResumed(Activity activity)
{
CrossCurrentActivity.Current.Activity = activity;
}
public void OnActivitySaveInstanceState(Activity activity, Bundle outState)
{
}
public void OnActivityStarted(Activity activity)
{
CrossCurrentActivity.Current.Activity = activity;
}
public void OnActivityStopped(Activity activity)
{
}
}

From the Android docs, it states this:
If it has declared its launch mode to be "multiple" (the default) and
you have not set FLAG_ACTIVITY_SINGLE_TOP in the same intent, then it
will be finished and re-created; for all other launch modes or if
FLAG_ACTIVITY_SINGLE_TOP is set then this Intent will be delivered to
the current instance's onNewIntent().
That's why your app is restarting.
The launchMode attribute of the activity affects how the activity is launched.
singleTop, singleTask, or singleInstance should be used to prevent the notification intent from creating a new activity instance.
The flag FLAG_ACTIVITY_NEW_TASK doesn't influence a new activity being created, but makes the launched activity the root of a new task.
For more, check:
https://developer.android.com/guide/topics/manifest/activity-element.html#lmode
https://developer.android.com/guide/components/activities/tasks-and-back-stack

Xamarin Android: Set ExpandableListView.SetOnGroupExpandListener

I want to set a listener for ExpandableList. I have searched around but found only android specific following code. How can I convert the following android code to Xamarin.
ExpandableList expListView; // suppose it is initilized
expListView.setOnGroupExpandListener(new IOnGroupExpandListener() {
int previousItem = -1;
#Override
public void onGroupExpand(int groupPosition)
{
if (groupPosition != previousItem)
expandableList.collapseGroup(previousItem);
previousItem = groupPosition;
}
});

You can implement the interface ExpandableListView.IOnGroupExpandListener on the Activity (or Fragment) or as a separate Java-based object.
Activity Example:
public class MainActivity : Activity, ExpandableListView.IOnGroupExpandListener
{
~~~
ExpandableListView expListView;
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
expListView.SetOnGroupExpandListener(this);
}
~~~
public void OnGroupExpand(int groupPosition)
{
// implement your onexpand code
}
~~~
}
Separate Class:
public class MyExpander : Java.Lang.Object, ExpandableListView.IOnGroupExpandListener
{
public void OnGroupExpand(int groupPosition)
{
// implement your onexpand code
}
}

How to call same service instance from multiple activities in Android

I've just started looking into Xamarin and just can not to wrap around my head how to make multiple Activities have a reference same instance of service.
I am starting KeyPressedReceiver from MainActivity and start listening for power button being pressed.
When three click are being made, I am calling service method InitCancelActivity, which starts playing mp3 file and opens CancelActivity.
In CancelActivity there is a text field and a button. And when user press this button, I want the value from text field to be passes to the GeneralService method KillAlert.
The question is how to reference instance of GeneralService (which is already created) from CancelActivity, so I could call KillAlert?
And this part
if (_service == null)
_service = new GeneralService();
looks absolutely wrong. Should I instantiate it in MainActivity and pass to a KeyPressedReceiver constructor?
[Activity(Label = "TTTT", MainLauncher = true, Icon = "#drawable/icon")]
public class MainActivity : Activity
{
KeyPressedReceiver receiver;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
SetContentView(Resource.Layout.Main);
receiver = new KeyPressedReceiver();
RegisterReceiver(receiver, new IntentFilter(Intent.ActionScreenOn));
}
}
[BroadcastReceiver(Enabled = true)]
public class KeyPressedReceiver : BroadcastReceiver
{
private GeneralService _service;
private int _clicks = 0;
public override void OnReceive(Context context, Intent intent)
{
if (_service == null)
_service = new GeneralService();
_clicks++;
if (_clicks > 5)
{
_service.InitCancelActivity();
}
}
}
[Service(Name = "com.ff.GeneralService")]
public class GeneralService : Service {
private readonly Android.Media.MediaPlayer _player;
public GeneralService()
{
_player = new Android.Media.MediaPlayer();
}
public void RaiseAlert()
{
// start playing .mp3 file
}
public void KillAlert(string pass)
{
// stop playing .mp3 file
}
public void InitCancelActivity()
{
this.RaiseAlert();
var i = new Intent(this, typeof(CancelActivity));
i.SetFlags(ActivityFlags.NewTask);
this.StartActivity(i);
}
}
[Activity(Label = "CancelActivity")]
public class CancelActivity : Activity
{
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
SetContentView(Resource.Layout.cancel);
this.FindViewById(Resource.Id.cancelButtonYes).Click += delegate
{
var password = this.FindViewById(Resource.Id.cancelPassword);
// call KillAlert method from GeneralServic
};
}
}

Create static GeneralService instance and use in Cancel Activity.
for example
[Service(Name = "com.ff.GeneralService")]
public class GeneralService : Service {
private readonly Android.Media.MediaPlayer _player;
public static generalService;
public GeneralService()
{
_player = new Android.Media.MediaPlayer();
generalService=this
}
public void RaiseAlert()
{
// start playing .mp3 file
}
public void KillAlert(string pass)
{
// stop playing .mp3 file
}
public void InitCancelActivity()
{
this.RaiseAlert();
var i = new Intent(this, typeof(CancelActivity));
i.SetFlags(ActivityFlags.NewTask);
this.StartActivity(i);
}
}
and use in CancelActivity like below example
[Activity(Label = "CancelActivity")]
public class CancelActivity : Activity
{
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
SetContentView(Resource.Layout.cancel);
this.FindViewById(Resource.Id.cancelButtonYes).Click += delegate
{
var password = this.FindViewById(Resource.Id.cancelPassword);
// call KillAlert method from GeneralServic
GeneralService.generalService.KillAlert(password.TEXT);
};
}
}

How to get variable from another class to OnPrepare/CreateOptionsMenu

I have a simple wifi app. It is just scanning wifis and listing them. I figured out my ScanResult List is filling in another method but in OnPrepare/CreateOptionsMenu it is always null.
This method calls first when program starts I know that, but when i try to call it again with InvalidateOptionsMenu(); nothing changes. Here is my piec of code:
MainActivity:
public class MainActivity : Activity
{
public static Context context;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
SetContentView(Resource.Layout.Main);
Button wifiButton = FindViewById<Button>(Resource.Id.popupButton);
RegisterReceiver(new WiFiReceiver(), new IntentFilter(WifiManager.ScanResultsAvailableAction));
((WifiManager)GetSystemService(WifiService)).StartScan();
wifiButton.Click += (s, arg) => {
InvalidateOptionsMenu();
PopupMenu menu = new PopupMenu(this, wifiButton);
menu.Inflate(Resource.Menu.menu);
menu.Show();
};
}
public override bool OnCreateOptionsMenu(IMenu menu) {
WiFiReceiver wifiReceiver = new WiFiReceiver();
IList<ScanResult> availableWifis = wifiReceiver.GetWifiList();//This is always null
if (availableWifis != null) {
foreach (ScanResult token in availableWifis) {
menu.Add(token.Ssid);
}
}
return base.OnCreateOptionsMenu(menu);
}
}
WiFi Scanning this class:
class WiFiReceiver : BroadcastReceiver {
private IList<ScanResult> wifiList;
private string message;
public override async void OnReceive(Context context, Intent intent) {
MainActivity mainActivity = (MainActivity)context;
WifiManager wifiManager = (WifiManager)mainActivity.GetSystemService(Context.WifiService);
this.message = string.Join("\r\n", wifiManager.ScanResults
.Select(r => $"{r.Ssid} - {r.Level} dB"));
this.wifiList = wifiManager.ScanResults.ToList(); //This has connection informations
mainActivity.DisplayText(message);
await Task.Delay(TimeSpan.FromSeconds(1));
wifiManager.StartScan();
}
public IList<ScanResult> GetWifiList() {
return wifiList;
}

How to override OnLaunched() from Template10

I am trying to override the OnLaunched() function in a Template 10 Windows Application, but the problem is that it is sealed in Template 10 BootStrapper class (which inherits from the Application class).
Here's my method:
using Windows.UI.Xaml;
...
namespace Sample {
...
sealed partial class App : Template10.Common.BootStrapper {
protected override void OnLaunched(LaunchActivatedEventArgs args)
{
/*************** My stuff *****************
***********************************************/
}
...
}
I am using Template10 Blank app for this app, and the OnLaunched() method in BootStrapper class is this:
namespace Template10.Common
{
public abstract class BootStrapper : Application
{
...
protected sealed override void OnLaunched(LaunchActivatedEventArgs e);
...
}
...
}
I cannot remove the sealed modifier from OnLaunched() in BootStrapper (guess because it is "from metadata").
What's the point of including a sealed method in an abstract class?
Do we get some other method to override, like OnResume(), OnStartAsync(), etc, instead of OnLaunched()?
Update: For reference, here are all the members in BootStrapper:
public abstract class BootStrapper : Application
{
public const string DefaultTileID = "App";
protected BootStrapper();
public static BootStrapper Current { get; }
public TimeSpan CacheMaxDuration { get; set; }
public INavigationService NavigationService { get; }
public StateItems SessionState { get; set; }
public bool ShowShellBackButton { get; set; }
protected Func<SplashScreen, UserControl> SplashFactory { get; set; }
public event EventHandler<WindowCreatedEventArgs> WindowCreated;
public static AdditionalKinds DetermineStartCause(IActivatedEventArgs args);
public NavigationService NavigationServiceFactory(BackButton backButton, ExistingContent existingContent);
[AsyncStateMachine(typeof(<OnInitializeAsync>d__44))]
public virtual Task OnInitializeAsync(IActivatedEventArgs args);
public virtual void OnResuming(object s, object e);
public abstract Task OnStartAsync(StartKind startKind, IActivatedEventArgs args);
[AsyncStateMachine(typeof(<OnSuspendingAsync>d__45))]
public virtual Task OnSuspendingAsync(object s, SuspendingEventArgs e);
public Dictionary<T, Type> PageKeys<T>() where T : struct, IConvertible;
public virtual T Resolve<T>(Type type);
public virtual INavigable ResolveForPage(Type page, NavigationService navigationService);
public void UpdateShellBackButton();
[AsyncStateMachine(typeof(<OnActivated>d__26))]
protected sealed override void OnActivated(IActivatedEventArgs e);
[AsyncStateMachine(typeof(<OnCachedFileUpdaterActivated>d__27))]
protected sealed override void OnCachedFileUpdaterActivated(CachedFileUpdaterActivatedEventArgs args);
[AsyncStateMachine(typeof(<OnFileActivated>d__28))]
protected sealed override void OnFileActivated(FileActivatedEventArgs args);
[AsyncStateMachine(typeof(<OnFileOpenPickerActivated>d__29))]
protected sealed override void OnFileOpenPickerActivated(FileOpenPickerActivatedEventArgs args);
[AsyncStateMachine(typeof(<OnFileSavePickerActivated>d__30))]
protected sealed override void OnFileSavePickerActivated(FileSavePickerActivatedEventArgs args);
protected sealed override void OnLaunched(LaunchActivatedEventArgs e);
[AsyncStateMachine(typeof(<OnSearchActivated>d__31))]
protected sealed override void OnSearchActivated(SearchActivatedEventArgs args);
[AsyncStateMachine(typeof(<OnShareTargetActivated>d__32))]
protected sealed override void OnShareTargetActivated(ShareTargetActivatedEventArgs args);
protected sealed override void OnWindowCreated(WindowCreatedEventArgs args);
public enum AdditionalKinds
{
Primary,
Toast,
SecondaryTile,
Other
}
public enum BackButton
{
Attach,
Ignore
}
public enum ExistingContent
{
Include,
Exclude
}
public enum StartKind
{
Launch,
Activate
}
}
Please help :}

Template 10 does not allow us to override OnLaunched() method. Instead we can override the OnInitializeAsync() and OnStartAsync() methods for this purpose.
The reason is that Template 10 recommends us to use something called the Single Page Model, which is nothing but using a single instance of the Page class to put in the empty Frame provided by the Framework. How is that benefit to us? Well, if we need to put a menu, say a Hamburger menu, in our app, then we need to copy the code for the menu in each and every page we create in our app. This would lead to things like redundancy, inconsistency, WET code, etc. etc.
Therefore, template 10, initially, creates a Page, which they call the Shell, and then contents of each page is loaded into this Shell page, instead of creating new Pages.
We can override these methods in the following way:
sealed partial class App : BootStrapper
{
public App()
{
this.InitializeComponent();
}
public override Task OnInitializeAsync(IActivatedEventArgs args)
{
var nav = NavigationServiceFactory(BackButton.Attach, ExistingContent.Include);
Window.Current.Content = new Views.Shell(nav);
return Task.FromResult<object>(null);
}
public override Task OnStartAsync(BootStrapper.StartKind startKind, IActivatedEventArgs args)
{
NavigationService.Navigate(typeof(Views.MainPage));
return Task.FromResult<object>(null);
}
}
Here's where I figured the answer:
https://github.com/Windows-XAML/Template10/wiki/Docs-%7C-HamburgerMenu
So, long story short, override OnInitializeAsync() or OnStartAsync(), instead of OnLaunched().

You're trying to override OnLaunched in MyPage.xaml.cs and I'm pretty safe to assume that your MyPage class does not inherit from Application. So it does not have OnLaunched() method (at least not with that signature). What you need to do is override it in App.xaml.cs, as it's Application.OnLaunched(). App class, which is in App.xaml.cs, inherits from Application.
By the way, this is the example from the blank app template, which you've mentioned: