Bluetooth LE Scan fails in the background - permissions
The problem was not the scan filter, but background permissions.
Android 10-11:
In order to detect BLE devices in the background, you must have several permissions in the manifest. Place the following in your AndroidManifest.xml:
<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.ACCESS_BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.ACCESS_BACKGROUND_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
Then add code like follows to your Activity to dynamically request these permissions from the user:
private static final int PERMISSION_REQUEST_FINE_LOCATION = 1;
private static final int PERMISSION_REQUEST_BACKGROUND_LOCATION = 2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (this.checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
if (this.checkSelfPermission(Manifest.permission.ACCESS_BACKGROUND_LOCATION)
!= PackageManager.PERMISSION_GRANTED) {
if (this.shouldShowRequestPermissionRationale(Manifest.permission.ACCESS_BACKGROUND_LOCATION)) {
final AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("This app needs background location access");
builder.setMessage("Please grant location access so this app can detect beacons in the background.");
builder.setPositiveButton(android.R.string.ok, null);
builder.setOnDismissListener(new DialogInterface.OnDismissListener() {
@TargetApi(23)
@Override
public void onDismiss(DialogInterface dialog) {
requestPermissions(new String[]{Manifest.permission.ACCESS_BACKGROUND_LOCATION},
PERMISSION_REQUEST_BACKGROUND_LOCATION);
}
});
builder.show();
}
else {
final AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Functionality limited");
builder.setMessage("Since background location access has not been granted, this app will not be able to discover beacons in the background. Please go to Settings -> Applications -> Permissions and grant background location access to this app.");
builder.setPositiveButton(android.R.string.ok, null);
builder.setOnDismissListener(new DialogInterface.OnDismissListener() {
@Override
public void onDismiss(DialogInterface dialog) {
}
});
builder.show();
}
}
} else {
if (!this.shouldShowRequestPermissionRationale(Manifest.permission.ACCESS_FINE_LOCATION)) {
requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION,
Manifest.permission.ACCESS_BACKGROUND_LOCATION},
PERMISSION_REQUEST_FINE_LOCATION);
}
else {
final AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Functionality limited");
builder.setMessage("Since location access has not been granted, this app will not be able to discover beacons. Please go to Settings -> Applications -> Permissions and grant location access to this app.");
builder.setPositiveButton(android.R.string.ok, null);
builder.setOnDismissListener(new DialogInterface.OnDismissListener() {
@Override
public void onDismiss(DialogInterface dialog) {
}
});
builder.show();
}
}
}
}
When you prompt the user for location permission, the OS dialog will give them the option to downgrade that permission request to "Allow Only While Using the App" vs. "Allow All the Time". If the user chooses the first option, you will not get detections in the background, even if everything else above is set up.
On Android 11, things get more complex still, as the OS offers yet another option of "Only this time" for the permission request. If your app targets SDK 30 (Android 11), it won't even offer the user the option for "Allow All the Time", and the user will have to go to Settings as a separate step to turn on all the time access. See here for more details on the way this works on Android 11.
For a broader discussion of the evolution of permissions prompting, see my blog post here.
Before Android 10:
Starting with Android M, Bluetooth LE scanning in the background is blocked unless the app has one of the following two permissions:
android.permission.ACCESS_COARSE_LOCATION
android.permission.ACCESS_FINE_LOCATION
The app I was testing did not request either of these permissions, so it did not work in the background (the only time the scan filter was active) on Android M. Adding the first one solved the problem.
I realized this was the problem because I saw the following line in Logcat:
09-22 22:35:20.152 5158 5254 E BluetoothUtils: Permission denial: Need ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION permission to get scan results
See here for details: https://code.google.com/p/android-developer-preview/issues/detail?id=2964
I had a similar problem with an app connecting to bluetooth. Not LE ScanFilter, but it was a permissions issue just like the OP had.
Root cause is that starting with SDK 23, you need to prompt the user for permissions at runtime using Activity's requestPermissions() method.
Here's what worked for me:
Add one of the following two lines to
AndroidManifest.xml, inside the root node:<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />In your Activity, before attempting to connect to bluetooth, call
Activity'srequestPermissions()method, which opens a system dialog to prompt the user for the permission. The permissions dialog opens in a different thread, so be sure to wait for the result before trying to connect to bluetooth.Override
Activity'sonRequestPermissionsResult()to handle the result. This method will really only need to do something if the user refused to grant the permission, to tell the user that the app can't do the bluetooth activity.
This blog post has some example code that uses AlertDialogs to tell the user what's going on. It is a good starting point but has some shortcomings:
- It doesn't handle waiting for the
requestPermissions()thread to finish - The AlertDialog wrapping the call to
requestPermissions()seems extraneous to me. A bare call torequestPermissions()is sufficient.