Develop Reference

Android BroadcastReceiver returns zero

I make a broadcast call on my Android 10 device, but it returns zero. I tried the suggested solutions but they didn't work. How can I solve it?
manifest
<application
<receiver android:name=".ExampleReceiver" android:exported="true">
<intent-filter>
<action android:name="com.example.myapplication.Test"/>
</intent-filter>
</receiver>
</application>
ExampleReceiver.java
public class ExampleReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
String test = "Hello World";
setResultData(test);
}
}
am broadcast -a com.example.myapplication.Test
Broadcasting: Intent { act=com.example.myapplication.Test flg=0x400000 }
Broadcast completed: result=0

Documentation says
If your app targets API level 26 or higher, you cannot use the
manifest to declare a receiver for implicit broadcasts (broadcasts
that do not target your app specifically), except for a few implicit
broadcasts that are exempted from that restriction. In most cases, you
can use scheduled jobs instead.
So you need to register your receiver in code.
registerReceiver(new ExampleReceiver(), new IntentFilter("com.example.myapplication.Test"));

Android implicit BroadcastReceiver with signature permission is not called in Android O

In my first application, I define a custom permission and an implicit BroadcastReceiver in manifest file:
<permission
android:name="com.example.test.TEST"
android:protectionLevel="signature" />
<receiver
android:name=".TestBroadcastReceiver"
android:enabled="true"
android:exported="true"
android:permission="com.example.test.TEST">
<intent-filter>
<action android:name="com.example.test.TEST_RECEIVER" />
</intent-filter>
</receiver>
And this is the TestBroadcastReceiver.java:
public class TestBroadcastReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
Log.d("Test", "Hello World!");
Toast.makeText(context, "Hello World!", Toast.LENGTH_LONG).show();
}
}
In my second app, I've added the permission in manifest file:
<uses-permission android:name="com.example.test.TEST" />
And here, I send the broadcast:
getActivity().sendBroadcast(new Intent("com.example.test.TEST_RECEIVER"));
But nothing is called in first app. I know we can't use implicit broadcast in android O and above but according to here, there is an exception for broadcasts that require a signature permission:
Broadcasts that require a signature permission are exempted from this
restriction, since these broadcasts are only sent to apps that are
signed with the same certificate, not to all the apps on the device.
So how can I signal my other apps in android O?

According to CommonsWare answer, the problem is that I was missing setPackage() part. So I changed the code as below and now broadcast is received:
getActivity().sendBroadcast(new Intent("com.example.test.TEST_RECEIVER").setPackage("com.example.test"));

Android Broadcastreceiver not working?

I'm trying to use a broadcastreceiver to capture a network change but it doesn't seem to be working at all.
My broadcastreceiver:
public class btReceiver extends BroadcastReceiver {
public btReceiver() {
}
#Override
public void onReceive(Context context, Intent intent)
{
Log.d("BB","Received!");
Toast.makeText(context, "Action: " + intent.getAction(), Toast.LENGTH_LONG);
}
}
The way I call it:
IntentFilter filter = new IntentFilter();
filter.addAction(getPackageName() + "android.net.conn.CONNECTIVITY_CHANGE");
btReceiver myReceiver = new btReceiver();
registerReceiver(myReceiver, filter);
But when I try to toggle let's say wifi, nothing happens at all. I also tried declaring it in the manifest like so:
<receiver android:name=".btReceiver" android:enabled="true" >
<intent-filter>
<action android:name="android.net.conn.CONNECTIVITY_CHANGE" />
</intent-filter>
</receiver>
But that also doesn't work.
I have declared sufficient permissions in my manifest:
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
My test device is running Android 7.1.1, does anyone know why it's not firing?

Apps targeting Android N (Nougat) do not receive CONNECTIVITY_ACTION broadcasts, even if they have manifest entries to request notification of these events. Apps that are running can still listen for CONNECTIVITY_CHANGE on their main thread if they request notification with a BroadcastReceiver.
You should register it programmatically or use JobScheduler, GcmNetworkManager or android-job library

Your package name shouldn't be part of the Intent action. So try with:
filter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
Even better, there's a constant for that:
filter.addAction(ConnectivityManager.CONNECTIVITY_ACTION);

How to detect Bluetooth state change using a broadcast receiver?

I am trying to make an app that shows a toast when the device's Bluetooth turned on. I wanna do that even when my app is not running. So I should use a broadcast receiver, add some permissions, an intent-filter to android manifest and make a java class but I don't know the details.
What should I do? Which permissions should I use?

AS far as permissions go, to detect the state change of bluetooth you need to add this to your AndroidManifest.xml.
<uses-permission android:name="android.permission.BLUETOOTH" />
An example receiver would look like this, you add this code to where you want to handle the broadcast, for example an activity:
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
public void onReceive (Context context, Intent intent) {
String action = intent.getAction();
if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
if(intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, -1)
== BluetoothAdapter.STATE_OFF)
// Bluetooth is disconnected, do handling here
}
}
};
To use the receiver, you need to register it. Which you can do as follows. I register the receiver in my main activity.
registerReceiver(this, new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED));
You could also decide to add all of it to your AndroidManifest.xml. This way you can make a special class for the receiver and handle it there. No need to register the receiver, just make the class and add the below code to the AndroidManifest
<receiver
android:name=".packagename.NameOfBroadcastReceiverClass"
android:enabled="true">
<intent-filter>
<action android:name="android.bluetooth.adapter.action.STATE_CHANGED"/>
</intent-filter>
</receiver>

You have to take following permission.
<uses-permission android:name="android.permission.BLUETOOTH" />
and you have to write this as your intent filter in receiver tag.
<action android:name="android.bluetooth.adapter.action.STATE_CHANGED" />

Unfortunately, for apps targeting api 26 or higher, manifest declared broadcast receivers don't work anymore (reference here: https://developer.android.com/guide/components/broadcast-exceptions), with some exceptions.
android.bluetooth.adapter.action.STATE_CHANGED is not in that list.
For bluetooth, you can only listen for changes on:
ACTION_CONNECTION_STATE_CHANGED, ACTION_ACL_CONNECTED, ACTION_ACL_DISCONNECTED

How to set permissions in broadcast sender and receiver in android

How do we specify in broadcast sending application that which application can receive this broadcast, and in receiving application that which particular application has the permission to send broadcast to its broadcast receiver...
I am new to android..I read the documentation etc on internet but couldn't find the syntax to specify these permissions.

To control who is able to receive the broadcast message, you can use the method sendBroadcast:
public abstract void sendBroadcast (Intent intent, String receiverPermission)
where you precise the name of the required permission. If the receiver does not declare this permission, it will not be able to get the message. For example, the broadcast sender can do:
Intent broadcast = new Intent(this, MyBroadcastReceiver.class);
sendBroadcast(broadcast, "andro.jf.mypermission");
In the manifest of the broadcast sender, a new permission should be declared:
<!-- Declaring the special permission -->
<permission android:name="andro.jf.mypermission"
android:label="my_permission"
android:protectionLevel="dangerous"></permission>
Then, in the application that is supposed to receive this broadcast, you have to declare this permission and say that you use it. In the manifest you can add:
<!-- I use the permission ! -->
<uses-permission android:name="andro.jf.mypermission"/>
and of course, you have to declare your broadcast receiver:
<receiver android:name="MyBroadcastReceiver" android:exported="true" />
You can have a look at this post for a complete example of a custom permission and also the android developer page about this. Be carefull with the order of installation of your apps because the one that defines the permission should be installed first.

If you want to restrict who only can send intents to your broadcast receiver, do it this way:
The broadcast receiver:
<manifest ...>
<!-- Permission declaration -->
<permission android:name="my.app.PERMISSION" />
<receiver
android:name="my.app.BroadcastReceiver"
android:permission="my.app.PERMISSION"> <!-- Permission enforcement for delivering intents to this receiver -->
<intent-filter>
<action android:name="my.app.Action" />
</intent-filter>
</receiver>
...
</manifest>
The broadcast sender:
<manifest ...>
<!-- We declare we own the permission to send broadcast to the above receiver -->
<uses-permission android:name="my.app.PERMISSION" />
...
</manifest>
Sending broadcast from the sender Activity to the receiver:
Intent intent = new Intent();
intent.setAction("my.app.Action");
activity.sendBroadcast(intent);
If you declare the permission like this:
<permission android:protectionLevel="signature" android:name="my.app.PERMISSION" />
Then the sender will be able to use this permission and send broadcasts to receiver only when both the sender and the receiver apps are signed by the same developer certificate.

Declare permission
First you need declare your permission in your AndroidManifest.xml
<permission android:name="YOUR_PERMISSION_STRING" android:protectionLevel="signature"/>
<uses-permission android:name="com.codylab.photogallery.PRIVATE"/>
the android:name value is used as permission value and will used later.
Usage
There are two kinds of permission usages related to broadcast receiver:
(1) Control which application can receive your broadcast:
String PERMISSION_STRING_PRIVATE_RECEIVER = "YOU_NEED_THIS_TO_RECEIVE_THIS_BROADCAST"
sendBroadcast(intent, PERMISSION_STRING_PRIVATE_RECEIVER);
With this usage, you can control only authorized application can handle the broadcast you sent.
(2) Only handle the broadcasts have the specified permission
String PERMISSION_STRING_PRIVATE_BROADCASTER = "ONLY HANDLE BROADCASTS WITH THIS PERMISSION"
IntentFilter filter = new IntentFilter(ACTION_SAMPLE);
registerReceiver(mReceiver, filter, PERMISSION_STRING_PRIVATE_BROADCASTER, null);
With this usage, you can make sure that the broadcaster is authorized.

use an intent filter in receiver tag in manifest
<receiver
android:name="Your receiver"
android:enabled="true"
android:exported="false" >
<intent-filter>
<action android:name="action"/>
<category android:name="category" />
</intent-filter>
</receiver>
To send broadcast to app
Intent intent = new Intent();
intent.setAction("use same action in receiver");
intent.addcategory("use same category in receiver");
context.sendBroadcast(intent);

After half day search and test, based on #JFL's answer, I find the sender app must add both <permission> tag and <uses-permission> tag, then the receiver can receive the broadcast with permission. Otherwise, the receiver app won't receive the broadcast.