Develop Reference

Always retain a single instance of my MainActivity (launcher app)

I'm currently working on an app that is supposed to replace the devices whole UI. Therefore I'm using <category android:name="android.intent.category.HOME"/> in order to call it whenever I press the home button, replacing the devices launcher.
This app should always have just one instance of its MainActivity running and when the home button is pressed, it shouldn't start a new Activity but resume to the existing one.
I've played with the different launchModes a bit and it looks like singleInstance is by best bet. But for some reason the home button gets rendered useless and I'm unabled to return the launcher. Sporadically sometimes it works and when it works, it works just like I've intended it to be.
standard launchmode starts a new instance of the launcher whenever I press the home button, which leads to several issues, since the launcher is supposed to do some things, like opening other apps and resuming to the launcher, whenever the MainActivity is created. This leads to a loop: launcher starts apps -> resumes to launcher by creating a new Activity -> launcher starts apps...
That behaviour could be fixed somehow, but still it doesn't solve the root of its cause
singleTop does the same.
singleTask does the same.
singleInstance retains the Activity and whenever I press the home button, the launcher just resumes with its last state. BUT for some reason, the home button sometimes doesn't work. Meaning that the App won't come to the foreground. Even closing all apps doesn't return me to the launcher -> the device kind of gets bricked since you can't do anything
Edit:
Couldn't really find a solution. I'm pretty sure it's a bug on googles side. I couldn't find the cause, but I've settled with a workaround.
I've created a new activitiy called "LoadingActivity" which literally only loads the activity:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_loading);
}
#Override
protected void onResume() {
super.onResume();
startActivity(new Intent(LoadingActivity.this,MainActivity.class));
}
The LoadingActivitys launchMode is "standard" while the "MainActivity" remains "singleInstance". This fixes everything for now. If I find a better solution in the future, I can simply delete the Activity and make the MainActivity the main activity again.
Edit2, per request, here's the manifest prior to the workaround:
<?xml version="1.0" encoding="utf-8"?>
<manifest
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
package="[package]">
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.REQUEST_DELETE_PACKAGES" />
<uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.REQUEST_INSTALL_PACKAGES"/>
<uses-permission android:name="android.permission.READ_LOGS" tools:ignore="ProtectedPermissions" />
<uses-permission android:name="android.permission.PACKAGE_USAGE_STATS" tools:ignore="ProtectedPermissions" />
<application
android:allowBackup="true"
android:icon="#drawable/logo"
android:label="#string/app_name"
android:roundIcon="#drawable/logo"
android:supportsRtl="false"
android:requestLegacyExternalStorage="true"
android:theme="#style/AppTheme">
<activity
android:name="[package].MainActivity"
android:launchMode="singleInstance"
android:excludeFromRecents="true"
android:alwaysRetainTaskState="true"
android:configChanges="uiMode|fontScale">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
<category android:name="android.intent.category.HOME" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<service android:name=".MediaServiceBrowser">
<intent-filter>
<action android:name="android.intent.action.MEDIA_BUTTON" />
<action android:name="android.media.AUDIO_BECOMING_NOISY" />
<action android:name="android.media.browse.MediaBrowserService" />
</intent-filter>
</service>
<service android:name=".LocationService" />
<service
android:name=".NotificationListener"
android:enabled="true"
android:exported="true" android:permission="android.permission.BIND_NOTIFICATION_LISTENER_SERVICE">
<intent-filter>
<action android:name="android.service.notification.NotificationListenerService" />
</intent-filter>
</service>
<provider
android:name="androidx.core.content.FileProvider"
android:authorities="${applicationId}.provider"
android:exported="false"
android:grantUriPermissions="true">
<meta-data android:name="android.support.FILE_PROVIDER_PATHS"
android:resource="#xml/provider_paths" />
</provider>
</application>
</manifest>

"Default activity not found"

I keep getting the "Default activity is not found" error whenever I want to try and run my app. I have tried 'clean project', 'invalidate caches/restart' and restarted my computer.
UPDATE: I tried running different projects, but they all give the same error too. This makes me think there must be something wrong with settings.
It works perfectly for my friend, but I get the error that the "Default activity is not found". If I try to launch a specific activity it also says the activity is not found. This is the code in the androidmanifest.xml file:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
package="ek97.fhict.theapp">
<!-- To auto-complete the email text field in the login form with the user's emails -->
<uses-permission android:name="android.permission.GET_ACCOUNTS" />
<uses-permission android:name="android.permission.READ_PROFILE" />
<uses-permission android:name="android.permission.READ_CONTACTS" />
<!--
The ACCESS_COARSE/FINE_LOCATION permissions are not required to use
Google Maps Android API v2, but you must specify either coarse or fine
location permissions for the 'MyLocation' functionality.
-->
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission. ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="#drawable/loqate_logo"
android:label="#string/app_name"
android:roundIcon="#drawable/loqate_logo"
android:supportsRtl="true"
android:theme="#style/AppTheme"
tools:ignore="GoogleAppIndexingWarning">
<activity
android:name=".bottomnavigationfinal"
android:label="#string/title_activity_bottomnavigationfinal"/>
<activity android:name="Settings" />
<activity
android:name=".Login"
android:label="#string/title_activity_login" />
<activity
android:name=".Registration"
android:exported="true"
android:label="#string/title_activity_registration" />
<activity android:name=".Navigation" />
<activity android:name=".SplashScreen">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!--
The API key for Google Maps-based APIs is defined as a string resource.
(See the file "res/values/google_maps_api.xml").
Note that the API key is linked to the encryption key used to sign the APK.
You need a different API key for each encryption key, including the release key that is used to
sign the APK for publishing.
You can define the keys for the debug and release targets in src/debug/ and src/release/.
-->
<activity
android:name=".GoogleMaps"
android:label="#string/title_activity_google_maps" >
<meta-data
android:name="com.google.android.geo.API_KEY"
android:value="#string/google_maps_key" />
</activity>
<activity android:name=".Profile" />
</application>
</manifest>

If it works for your friend and it is the same code it could be that all you need to do is to refresh the cache of your IDE:
File -> Invalidate Caches / Restart

Try this::
Your manifest is missing default activity
Add to any activity as you consider a default activity
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>

I finally solved it by making sure all implementation versions were the same, there were some in a 28.0.0 version and others in a 26.1.0. version. Now the app works fine on the emulator. Thanks for your suggestions though

Android App Won't Remember USB Permission

I am trying to stop the app I am working on from asking for USB permissions each time the USB device is disconnected. I have followed: USB device access pop-up suppression? without much luck.
The app does remember the USB device until the device is unplugged.
If it matters I am trying to connect the app to an Arduino Teensy.
This is what my manifest activity looks like
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<intent-filter> <!-- For receiving data from another application -->
<action android:name="android.intent.action.SEND" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="text/plain" />
</intent-filter>
<intent-filter>
<action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"/>
</intent-filter>
<meta-data android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" android:resource="#xml/usb_device_filter" />
</activity>
</application>
And here is my usb_device_filter file:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<usb-device vendor-id="--hidden--" product-id="--hidden--" />
</resources>
Any help is welcome.
EDIT: I also look over at the Android Developer page and they say when using an intent filter for USB connections: If users accept, your application automatically has permission to access the device until the device is disconnected.
I would also like to point out that the suggested duplicate does not have the same issue as I am trying to solve. Their problem is having two activities while my problem deals with just one.
https://developer.android.com/guide/topics/connectivity/usb/host

We ended up opening the app automatically when the USB is inserted into the phone, because our project deals with the app being open all day.
The app only asks for permission to use the USB once for the phone and remembers it now, as long as the user connects the USB before opening the app and the phone is unlocked. The phone even remembers the permission after the phone is restarted.
This is kind of a work around, but it works for our needs. Hopefully this will help some others with the same problem.

As the asker here says, For your perpose (if I understood correctly) the following should be enough. That's right that he had a different problem but he started hes question saying that for your case it's working.
<activity android:name=".FirstActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
<action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
</intent-filter>
<meta-data
android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"
android:resource="#xml/usb_device_filter" />
</activity>

Broadcast Receiver not working when app is not running

My broadcast receiver does not work when the application is not running in the background.
Tried with different intent filters
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:supportsRtl="true"
android:theme="#style/AppTheme.NoActionBar" >
<receiver android:name=".network.NetworkChangeReceiver"
android:enabled="true">
<intent-filter>
<action android:name="android.net.conn.CONNECTIVITY_CHANGE" />
</intent-filter>
</receiver>
<activity
android:name=".view.activity.MainActivity"
android:label="#string/app_name">
</activity>
<activity android:name=".view.activity.BarLoginActivity"
android:label="#string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
My receiver works fine when the app is running in the background but as soon as I remove my recent apps it does not work.
Running on API 19

Finally it worked in other android phones.
as broadcast receivers and services are by default not allowed in Xiaomi phones

I would try putting a android:process=":remote" in the Manifest definition of the receiver so that it will run on a separate task.

Haven't seen your entire AndroidManifest but my first suspect is that you're lacking the proper permission.
In order to listen to network changes you must declare that you are using this permission in the manifest like this
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
the next suspect is the name you gave, maybe try giving the full path to the reciever name

Creating a new Activity, makes a whole new application?

Im new to android, and when i read "Create New Activity" i was under the impression it creates a new "Window/Layout/Screen".
When i start making my own application i see
Main.java
is one application and
SecondActivity.java
is another app in my Emulators menu?
Why is that and how can i go about making one app with multiple windows as apposed to multiple applications essentially?
Manifest
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.ryan.bidorbuyapp" >
<application
android:allowBackup="true"
android:icon="#mipmap/bidorbuy_logo"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".FullscreenActivity"
android:configChanges="orientation|keyboardHidden|screenSize"
android:label="#string/app_name"
android:theme="#style/FullscreenTheme" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".SearchResults"
android:configChanges="orientation|keyboardHidden|screenSize"
android:label="#string/title_activity_search_results"
android:parentActivityName=".FullscreenActivity"
android:theme="#style/FullscreenTheme" >
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.ryan.bidorbuyapp.FullscreenActivity" />
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
thanks

Look at your AndroidManifest.xml there is the problem. Your activities have Launcher between it's tags. Only one activity must have LAUNCHER tag
Only one activity must have
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>

You should understand what is an Activity before starting to developing an android application. You can think an activity as a page in web. There can be one or more and every activity includes their own contents.
When you create a new activity in your project, you should navigate by doing some operations in another activity. Intent helps you at this point to navigate one activity to the another.
Your problem is that, you should check your AndroidManifest.xml file. Please check the declaration of intent here. I think you will solve it after making a search about Intent.