Android BLE: “Scan failed, reason app registration failed for UUID”

Android BLE: “Scan failed, reason app registration failed for UUID”

Understanding the Error

The error “Scan failed, reason app registration failed for UUID” typically occurs when your Android app attempts to scan for Bluetooth Low Energy (BLE) devices using the `BluetoothAdapter.startLeScan()` method and fails due to an issue with the app’s registration for the specified UUIDs.

Causes of the Error

The error can stem from various reasons:

* **Incorrect UUID Format:** Make sure the UUID you’re using in your app registration is formatted correctly. The UUID must be a 128-bit value represented as a String.
* **Mismatched UUIDs:** The UUIDs used during app registration must match the UUIDs advertised by the BLE devices you want to scan.
* **App Registration Issue:** The app’s registration process might not have been completed successfully.
* **Device Permissions:** Your Android app needs the necessary permissions to scan for BLE devices, including “ACCESS_COARSE_LOCATION” and “BLUETOOTH_ADMIN”.
* **Multiple App Registrations:** Having multiple apps registered with the same UUID might lead to conflicts.

Troubleshooting and Solutions

Here’s how to troubleshoot and address the error:

1. Verify UUID Format

* Double-check the UUID you’re using in your app registration and make sure it’s a valid 128-bit UUID string.
* For example: `String uuidString = “0000180d-0000-1000-8000-00805f9b34fb”;`

2. Match UUIDs

* Ensure that the UUIDs you’re registering with the Bluetooth Manager are the same as the UUIDs advertised by the BLE devices.
* You can discover the advertised UUIDs by using a BLE scanner app.

3. Review App Registration

* **Using `BluetoothAdapter.startLeScan(UUID[])`:**
* Ensure you’re providing the correct UUIDs in the `UUID[]` array during the `startLeScan()` call.
* **Using `BluetoothLeScanner.startScan(List, ScanSettings)`:**
* When using the newer `BluetoothLeScanner`, make sure the `ScanFilter` objects correctly include the desired service and characteristic UUIDs.

4. Check Permissions

* In your AndroidManifest.xml file, add the following permissions:
“`xml



“`
* Request these permissions at runtime in your app.

5. Resolve Multiple Registrations

* If multiple apps are trying to register with the same UUID, consider using different UUIDs or coordinate registration between apps.

6. Debugging Tips

* Use the Android Debug Bridge (adb) logs to examine the BLE scan process.
* Check if your Bluetooth adapter is turned on and if you’re in a range that allows BLE communication.

Code Example

Using `BluetoothAdapter.startLeScan()`

“`java
// UUID for your desired BLE service
String uuidString = “0000180d-0000-1000-8000-00805f9b34fb”;
UUID serviceUUID = UUID.fromString(uuidString);

// Start scanning
BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
bluetoothAdapter.startLeScan(new UUID[] { serviceUUID }, new BluetoothAdapter.LeScanCallback() {
@Override
public void onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord) {
// Handle the scanned device
}
});
“`

Using `BluetoothLeScanner.startScan()`

“`java
// UUID for your desired service
String uuidString = “0000180d-0000-1000-8000-00805f9b34fb”;
UUID serviceUUID = UUID.fromString(uuidString);

// Create ScanFilter
ScanFilter filter = new ScanFilter.Builder()
.setServiceUuid(ParcelUuid.fromString(uuidString))
.build();

// Create ScanSettings
ScanSettings settings = new ScanSettings.Builder()
.setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
.build();

// Start scanning
BluetoothLeScanner scanner = bluetoothAdapter.getBluetoothLeScanner();
scanner.startScan(Collections.singletonList(filter), settings, new BluetoothAdapter.LeScanCallback() {
@Override
public void onScanResult(int callbackType, ScanResult result) {
// Handle the scanned device
}
});
“`

Conclusion

Addressing the “Scan failed, reason app registration failed for UUID” error usually involves ensuring correct UUID formatting, matching UUIDs between your app and BLE devices, reviewing app registration, confirming permissions, and handling potential conflicts with other apps. By carefully reviewing these aspects and implementing proper troubleshooting strategies, you can effectively resolve this error and successfully scan for BLE devices.