Bluetooth Low Energy Startscan on Android 6.0 Does Not Find Devices

BluetoothLeScanner.startScan with Android 6.0 does not discover devices

if permissions granted, have a try: turn ON the GPS.

Android BLE Scan never finds devices

The Problem

The problem is that you are only overriding the onBatchScanResults method and not onScanResult method. onBatchScanResults will only get triggered if:

1. You have set the ScanSettings mode to ScanSettings.SCAN_MODE_LOW_POWER (this is the default) using the ScanSettings.Builder.
2. You have set the report delay time to some value >0 using setReportDelay(long reportDelayMillis) in your ScanSettings.Builder.

reportDelayMillis - Delay of report in milliseconds. Set to 0 to be notified of results immediately. Values > 0 causes the scan results to be queued up and delivered after the requested delay or when the internal buffers fill up.

For example:

public void startScan(BluetoothLeScanner scanner) {
    ScanFilter filter = new ScanFilter.Builder().setDeviceName(null).build();

    ArrayList<ScanFilter> filters = new ArrayList<ScanFilter>();
                    filters.add(filter);

    ScanSettings settings = new ScanSettings.Builder()
                                .setScanMode(ScanSettings.SCAN_MODE_LOW_POWER)
                                .setReportDelay(1l)
                                .build();

    Log.i(TAG,"The setting are "+settings.getReportDelayMillis());
    scanner.startScan(filters,settings,BLEScan);
}

The Solution

However, you probably just want to get the results once at a time and not a batch of results. To accomplish that, you don't have to modify the ScanSettings, you just need to override the onScanResult method in your ScanCallback and that will do the trick.

private ScanCallback mScanCallback =
        new ScanCallback() {

    public void onScanResult(int callbackType, ScanResult result) {
        System.out.println(result.getDevice().getName())
        // Do whatever you want
    };

    ...
};

The Alternative - RxAndroidBle

Anyway, I highly recommend using the library RxAndroidBle. It is very well maintained and it solves many of the BLE issues out of the box (scanning is maybe the less complicated part in BLE).

Using that library, the scanning can be done like this:

Disposable scanSubscription = rxBleClient.scanBleDevices(

    new ScanSettings.Builder()
            // .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY) // change if needed
            // .setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES) // change if needed
            .build()
        // add filters if needed
)
    .subscribe(
        scanResult -> {
            // Process scan result here.
        },
        throwable -> {
            // Handle an error here.
        }
    );

// When done, just dispose.
scanSubscription.dispose();

Location needs to be enabled for Bluetooth Low Energy Scanning on Android 6.0

No, this is not a bug.

This issue was brought up to Google where they responded saying that this was the intended behavior and they won't fix it. They directed developers to this site where it points out that location permission is now needed for hardware identifier access. It is now the developer's responsibility to make their users aware of the requirement.

In the issue, however, it doesn't address why Location services (GPS, etc.) are required and it doesn't seem like they are going to revisit the issue to explain this since it has been marked as the intended behavior.

To answer the second part of the question: Yes, it is possible to scan without enabling Location services. You can do a Bluetooth classic scan using BluetoothAdapter.getDefaultAdapter().startDiscovery() and that will work with Location services off. This will discover all Bluetooth devices, BLE and otherwise. However, BLE devices won't have a scan record that they would have had if they were seen as a result of startScan().

Android 12: BLE Scan does not find any devices

I found the solution. Contrary to the statements in the official documentation you still need the android.permission.ACCESS_FINE_LOCATION and android.permission.ACCESS_COARSE_LOCATION permissions to be set in the Manifest and request them from the mobile user. Now everything works fine again.

Devices are not detected by Bluetooth LE scan

If device has BLE it does not mean that it will be visible (broadcast) any data by default. In order to achieve communication between two smart phones you need to have (install or write your own) application that uses BLE to create proper BLE service that will be exposed to other devices.

Some BLE capable devices such is iPhone for example broadcasts BAS (Battery Service) or similar, but I don't think that Android does.

So, don't expect to find any device on scan that you have described, and if you still need

to communicate two smartphones with Android 5.x through BLE

try to read Bluetooth Low Energy documentation and be ready to understand UUID, GATT, Characteristic...

BluetoothLescan() not finding any devices

Your code should work fine if you are scanning for BLE devices like a heart rate monitor or a proximity sensor. The problem could be that with this code your app is the GATT client and is searching for a GATT server.

So if you want to connect to another phone you could write a GATT server app and run it on the other phone (as indicated in the last paragraph here)

Bluetooth LE can't find any device on android 6.0

Yes you have to ask and be granted those permissions or else nothing will show up under runtime. But what i can see is that you are missing some dependencies on AppCompat

Add this to your build.gradle file

implementation  com.android.support:appcompat-v7:28.0.0

And also don't use implicit version number this will/can cause unpredicted errors because it can upgrade whenever without you knowing and introducing a nasty bug.
Set it always with a explicit number
'com.android.support:support-v4:28.0'

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