mainActivity

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import android.bluetooth.BluetoothAdapter; 
import android.bluetooth.BluetoothDevice; 
import android.content.BroadcastReceiver; 
import android.content.Context; 
import android.content.Intent; 
import android.content.IntentFilter; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.ArrayAdapter; 
import android.widget.Button; 
import android.widget.ListView; 
import android.widget.TextView; 
import android.widget.Toast; 
import java.util.Set; 
public class MainActivity extends AppCompatActivity 
{ 
private BluetoothAdapter bluetoothAdapter; 
Button scanButton; 
private static final int REQUEST_ENABLE_BT = 1; 
private ArrayAdapter<String> mNewDevicesArrayAdapter; 
@Override 
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) 
{ 
super.onActivityResult(requestCode, resultCode, data); 
if(resultCode == RESULT_CANCELED) Toast.makeText(this,"Please provide permission to turn on bluetooth",Toast.LENGTH_SHORT).show(); 
} 
@Override 
protected void onCreate(Bundle savedInstanceState) 
{ 
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); 
bluetoothAdapter = BluetoothAdapter.getDefaultAdapter(); 
if (bluetoothAdapter == null) 
{ 
Toast.makeText(this, "Device does not support bluetooth", Toast.LENGTH_SHORT).show(); 
finish();
} 
else if (!bluetoothAdapter.isEnabled())
{
Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}
scanButton = (Button) findViewById(R.id.button_scan);
scanButton.setOnClickListener(new View.OnClickListener() 
{ 
public void onClick(View v) 
{ 
doDiscovery(); 
v.setVisibility(View.GONE); 
} 
}); 
// Initialize array adapters. One for already paired devices and 
// one for newly discovered devices 
ArrayAdapter<String> pairedDevicesArrayAdapter = new ArrayAdapter<String>(this, R.layout.device_name); 
mNewDevicesArrayAdapter = new ArrayAdapter<String>(this, R.layout.device_name); 
// Find and set up the ListView for paired devices 
ListView pairedListView = (ListView) findViewById(R.id.paired_devices); 
pairedListView.setAdapter(pairedDevicesArrayAdapter); 
pairedListView.setOnItemClickListener(mDeviceClickListener); 
// Find and set up the ListView for newly discovered devices 
ListView newDevicesListView = (ListView) findViewById(R.id.new_devices);
newDevicesListView.setAdapter(mNewDevicesArrayAdapter); 
newDevicesListView.setOnItemClickListener(mDeviceClickListener); 
// Register for broadcasts when a device is discovered 
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND); 
this.registerReceiver(mReceiver, filter); 
// Register for broadcasts when discovery has finished 
filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED); 
this.registerReceiver(mReceiver, filter); 
// Get a set of currently paired devices 
Set<BluetoothDevice> pairedDevices = bluetoothAdapter.getBondedDevices(); 
// If there are paired devices, add each one to the ArrayAdapter 
if (pairedDevices.size() > 0) 
{ 
findViewById(R.id.title_paired_devices).setVisibility(View.VISIBLE); 
for (BluetoothDevice device : pairedDevices) 
{ 
pairedDevicesArrayAdapter.add(device.getName() + "\n" + device.getAddress());
}
}
else { 
String noDevices = "No paired devices found"; 
pairedDevicesArrayAdapter.add(noDevices);
} 
} 
@Override
protected void onDestroy() { super.onDestroy(); 
// Make sure we're not doing discovery anymore 
if (bluetoothAdapter != null) { bluetoothAdapter.cancelDiscovery(); 
} 
// Unregister broadcast listeners 
this.unregisterReceiver(mReceiver); 
}
private void doDiscovery() 
{ 
Log.d("TAG", "doDiscovery()");
// Indicate scanning in the title 
setProgressBarIndeterminateVisibility(true); 
setTitle("discovering new devices");
// Turn on sub-title for new devices 
findViewById(R.id.title_new_devices).setVisibility(View.VISIBLE); 
// If we're already discovering, stop it 
if (bluetoothAdapter.isDiscovering()) 
{ bluetoothAdapter.cancelDiscovery(); 
} 
// Request discover from BluetoothAdapter 
bluetoothAdapter.startDiscovery(); 
} 
private AdapterView.OnItemClickListener mDeviceClickListener = new AdapterView.OnItemClickListener() 
{ 
public void onItemClick(AdapterView<?> av, View v, int arg2, long arg3) 
{ 
// Cancel discovery because it's costly and we're about to connect 
bluetoothAdapter.cancelDiscovery();
Toast.makeText(getApplicationContext(),"Stopping discovery",Toast.LENGTH_SHORT).show();
// Get the device MAC address, which is the last 17 chars in the View String 
info = ((TextView) v).getText().toString();
String address = info.substring(info.length() - 17); 
// Create the result Intent and include the MAC address 
Intent intent = new Intent(MainActivity.this,LedControl.class); 
intent.putExtra("DEVICE_ADDRESS", address); 
// Set result and finish this Activity 
startActivity(intent);
}
}
; /** * The BroadcastReceiver that listens for discovered devices and changes the title when * discovery is finished */ 
private final BroadcastReceiver mReceiver = new BroadcastReceiver() { 
@Override 
public void onReceive(Context context, Intent intent) 
{ 
String action = intent.getAction();
// When discovery finds a device 
if (BluetoothDevice.ACTION_FOUND.equals(action)) 
{ 
// Get the BluetoothDevice object from the Intent 
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE); 
// If it's already paired, skip it, because it's been listed already 
if (device.getBondState() != BluetoothDevice.BOND_BONDED)
{ 
mNewDevicesArrayAdapter.add(device.getName() + "\n" + device.getAddress()); 
} 
// When discovery is finished, change the Activity title
} 
else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) 
{ 
setProgressBarIndeterminateVisibility(false); 
setTitle("Select a device to connect"); 
if (mNewDevicesArrayAdapter.getCount() == 0)
{ 
String noDevices = "No devices";
mNewDevicesArrayAdapter.add(noDevices); 
} 
}
}
};
}