Start Bluetooth Discoverable and register BroadcastReceiver for ACTION_SCAN_MODE_CHANGED

To enable Bluetooth Discoverable, we can start activity with intent of BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE. we can also provide expected discoverable duration via Extra.

To monitor the scan mode change in Bluetooth device, we can register our BroadcastReceiver for BluetoothAdapter.ACTION_SCAN_MODE_CHANGED. The BroadcastReceiver have t be unregister in onDestroy().

Here is a exercise to Start Bluetooth Discoverable.



AndroidBluetooth.java

package com.exercise.AndroidBluetooth;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

public class AndroidBluetooth extends Activity {
 
 private static final int REQUEST_ENABLE_BT = 1;
 private static final int REQUEST_Turn_On_Discoverable = 3;
 
    Spinner spnDiscoverableDuration;
 Button btnTurnOnDiscoverable;
 TextView stateBluetooth;
 BluetoothAdapter bluetoothAdapter;
 
 String[] optDiscoverableDur = {"10 sec", "60 sec", "120 sec", "240 sec", "300 sec"};
 int[] valueDiscoverableDur = {10, 60, 120, 240, 300};
 
 /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        spnDiscoverableDuration = (Spinner)findViewById(R.id.discoverableduration);
        btnTurnOnDiscoverable = (Button)findViewById(R.id.turnondiscoverable);
        
        stateBluetooth = (TextView)findViewById(R.id.bluetoothstate);
        bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        
        CheckBlueToothState();
        
        btnTurnOnDiscoverable.setOnClickListener(btnTurnOnDiscoverableOnClickListener);
        
        ArrayAdapter<String> adapterDiscoverableDur = new ArrayAdapter<String>(this,
          android.R.layout.simple_list_item_1, optDiscoverableDur);
        adapterDiscoverableDur.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spnDiscoverableDuration.setAdapter(adapterDiscoverableDur);

        registerReceiver(ScanModeChangedReceiver, 
          new IntentFilter(BluetoothAdapter.ACTION_SCAN_MODE_CHANGED));
    }
    
    @Override
 protected void onDestroy() {
  // TODO Auto-generated method stub
  super.onDestroy();
  unregisterReceiver(ScanModeChangedReceiver);
 }

 private void CheckBlueToothState(){
     if (bluetoothAdapter == null){
         stateBluetooth.setText("Bluetooth NOT support");
        }else{
         if (bluetoothAdapter.isEnabled()){
          if(bluetoothAdapter.isDiscovering()){
           stateBluetooth.setText("Bluetooth is currently in device discovery process.");
          }else{
           stateBluetooth.setText("Bluetooth is Enabled.");
           btnTurnOnDiscoverable.setEnabled(true);
          }
         }else{
          stateBluetooth.setText("Bluetooth is NOT Enabled!");
          Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
             startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
         }
        }
    }
    
    private Button.OnClickListener btnTurnOnDiscoverableOnClickListener
    = new Button.OnClickListener(){

  @Override
  public void onClick(View arg0) {
   // TODO Auto-generated method stub
   Intent discoverableIntent 
    = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
   int dur = valueDiscoverableDur[(int)spnDiscoverableDuration.getSelectedItemId()];
   discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, dur);
   startActivityForResult(discoverableIntent, REQUEST_Turn_On_Discoverable);
  }};

 @Override
 protected void onActivityResult(int requestCode, int resultCode, Intent data) {
  // TODO Auto-generated method stub
  if(requestCode == REQUEST_ENABLE_BT){
   CheckBlueToothState();
  }if (requestCode == REQUEST_Turn_On_Discoverable){
   if(resultCode == RESULT_OK){

   }else if (resultCode == RESULT_CANCELED){
    Toast.makeText(AndroidBluetooth.this, 
      "User Canceled", 
      Toast.LENGTH_LONG).show();
   }
  }
 }
    
 private final BroadcastReceiver ScanModeChangedReceiver = new BroadcastReceiver(){

  @Override
  public void onReceive(Context context, Intent intent) {
   // TODO Auto-generated method stub
   String action = intent.getAction();
   if(BluetoothAdapter.ACTION_SCAN_MODE_CHANGED.equals(action)) {
    
    int mode = intent.getIntExtra(BluetoothAdapter.EXTRA_SCAN_MODE, 
      BluetoothAdapter.ERROR);
    String strMode = "";
    
    switch(mode){
    case BluetoothAdapter.SCAN_MODE_CONNECTABLE_DISCOVERABLE:
     strMode = "mode changed: SCAN_MODE_CONNECTABLE_DISCOVERABLE";
     break;
    case BluetoothAdapter.SCAN_MODE_CONNECTABLE:
     strMode = "mode changed: SCAN_MODE_CONNECTABLE";
     break;
    case BluetoothAdapter.SCAN_MODE_NONE:
     strMode = "mode changed: SCAN_MODE_NONE";
     break;
    }
    
    Toast.makeText(AndroidBluetooth.this, 
      strMode, Toast.LENGTH_LONG).show();
         }
  }};
    
}

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
<TextView 
    android:id="@+id/bluetoothstate" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    />
<TextView
    android:id="@+id/bluetoothstate" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    />
<TextView
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="Set Discoverable Duration" 
    />
<Spinner
    android:id="@+id/discoverableduration" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    /> 
<Button
    android:id="@+id/turnondiscoverable" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    android:text="Turn on Discoverable" 
    android:enabled="false"
    /> 
</LinearLayout>

Grant permission of "android.permission.BLUETOOTH" in AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.exercise.AndroidBluetooth"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="7" />
    <uses-permission android:name="android.permission.BLUETOOTH"></uses-permission>

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".AndroidBluetooth"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

Download the files.

Related:
- Get the list of paired Bluetooth devices
- Scan Bluetooth Devices