MainActivity.java

package com.example.ble_imu_data_viewer;

import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContracts;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

import android.Manifest;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothGatt;
import android.bluetooth.BluetoothManager;
import android.bluetooth.le.BluetoothLeScanner;
import android.bluetooth.le.ScanCallback;
import android.bluetooth.le.ScanResult;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "important_info";
    private static final int REQUEST_ENABLE_BT = 13;
    private static final int REQUEST_ENABLE_BTSCAN = 14;
    private static final int REQUEST_ENABLE_BTCONNECT = 15;
    private boolean scanning;
    private Blocker blocker = new Blocker();
    private Handler handler = new Handler();
    private static final long SCAN_PERIOD = 10000;  // Stops scanning after 10 seconds.
    private BluetoothManager bluetoothManager;
    private BluetoothAdapter bluetoothAdapter;
    private BluetoothLeScanner bluetoothLeScanner;

    Set<BluetoothDevice> pairedDevices;
    ArrayList<BluetoothDevice> foundDevices;

    LinearLayout containerView;
    private BluetoothGatt bluetoothGatt;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Log.i(TAG, "In main activity.");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.i(TAG, "Called super method.");

        containerView = findViewById(R.id.container_view);

        bluetoothManager = getSystemService(BluetoothManager.class);
        bluetoothAdapter = bluetoothManager.getAdapter();
        if (bluetoothAdapter == null) {
            Log.e(TAG, "This device does not support Bluetooth.");
        }

        if (!bluetoothAdapter.isEnabled()) {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
                Log.i(TAG, "Bluetooth connect permission denied. Requesting...");
                ActivityCompat.requestPermissions(this, new String[]{"BLUETOOTH_CONNECT"}, REQUEST_ENABLE_BTCONNECT);
                return;
            }
            Log.i(TAG, "Bluetooth is disabled. Enabling...");
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
        }

        bluetoothLeScanner = bluetoothAdapter.getBluetoothLeScanner();

        scanLeDevice();
    }

    void connectBLEDevice(BluetoothDevice device) {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
            Log.i(TAG, "Bluetooth connect permission denied. Requesting...");
            ActivityCompat.requestPermissions(this, new String[]{"BLUETOOTH_CONNECT"}, REQUEST_ENABLE_BTCONNECT);
            return;
        }

        Log.i(TAG, "Connecting to " + device.getName() + "...");
        Log.i(TAG, "Going to DeviceControlActivity...");
        Intent goToConnectActivityIntent = new Intent(MainActivity.this, DeviceControlActivity.class);
        goToConnectActivityIntent.putExtra("DEVICE_ADDRESS", device.getAddress());
        startActivity(goToConnectActivityIntent);
    }

    private class LeDeviceListAdapter {

        public void addDevice(BluetoothDevice device) {
            foundDevices.add(device);

            Button buttonTemp = new Button(containerView.getContext());
            if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
                Log.i(TAG, "Bluetooth connect permission denied. Requesting...");
                ActivityCompat.requestPermissions(MainActivity.this, new String[]{"BLUETOOTH_CONNECT"}, REQUEST_ENABLE_BTCONNECT);
                return;
            }
            buttonTemp.setText(device.getName());
            buttonTemp.setId(foundDevices.size());
            buttonTemp.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    connectBLEDevice(foundDevices.get(buttonTemp.getId()));
                }
            });
            containerView.addView(buttonTemp);
        }

        public void notifyDataSetChanged() {
        }
    }

    private LeDeviceListAdapter leDeviceListAdapter = new LeDeviceListAdapter();
    // Device scan callback.
    private ScanCallback leScanCallback =
            new ScanCallback() {
                @Override
                public void onScanResult(int callbackType, ScanResult result) {
                    super.onScanResult(callbackType, result);
                    leDeviceListAdapter.addDevice(result.getDevice());
                    leDeviceListAdapter.notifyDataSetChanged();
                }
            };

    private void scanLeDevice() {
        if (!scanning) {
            // Stops scanning after a predefined scan period.
            handler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    scanning = false;
                    if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.BLUETOOTH_SCAN) != PackageManager.PERMISSION_GRANTED) {
                        Log.i(TAG, "Bluetooth scan permission denied. Requesting...");
                        requestPermissionLauncher.launch(Manifest.permission.BLUETOOTH_SCAN);
                        Log.i(TAG, "Permission requested. Awaiting user response");
                        return;
                    }
                    bluetoothLeScanner.stopScan(leScanCallback);
                }
            }, SCAN_PERIOD);

            scanning = true;
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_SCAN) != PackageManager.PERMISSION_GRANTED) {
                Log.i(TAG, "Bluetooth scan permission denied. Requesting...");
                requestPermissionLauncher.launch(Manifest.permission.BLUETOOTH_SCAN);
                Log.i(TAG, "Permission requested. Awaiting user response");
                return;
            }
            bluetoothLeScanner.startScan(leScanCallback);
            Log.i(TAG, "Scanning of BLE devices started.");
        } else {
            scanning = false;
            bluetoothLeScanner.stopScan(leScanCallback);
        }
    }

    // Register the permissions callback
    private ActivityResultLauncher<String> requestPermissionLauncher =
            registerForActivityResult(new ActivityResultContracts.RequestPermission(), isGranted -> {
                if (isGranted) {
                    Log.i(TAG, "Requested permission granted!");
                    scanLeDevice();
                } else {
                    Log.e(TAG, "Requested permission denied!");
                    Toast.makeText(this, "Permission denied! Sorry, we can't continue.", Toast.LENGTH_LONG);
                }
            });

    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        switch (requestCode) {
            case REQUEST_ENABLE_BT:
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    Log.i(TAG, "Bluetooth enabling permission successfully enabled!");
                    //TODO: Return to onCreate().
                } else {
                    Log.e(TAG, "Bluetooth enabling permission was NOT successfully enabled!");
                }
                break;

            case REQUEST_ENABLE_BTSCAN:
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    Log.i(TAG, "Bluetooth scan permission successfully enabled!");
                } else {
                    Log.e(TAG, "Bluetooth scan permission was NOT successfully enabled!");
                }
                break;

        }
    }

    private class Blocker{
        final void block() {
            inBlock = true;
            while(inBlock){

            }
        }

        final void endBlock(){
            inBlock = false;
        }

        private boolean inBlock = false;
    }
}