Develop Reference

Android Bluetooth for discover devices, method Broadcast receiver is never called

i have problem with this code everything works but when i press scan button nothing happens why is that, i'm sure this code is right i follow Bluetooth Android Developer tutorial, Upon debug, I found that the onReceive method of BroadcastReceiver is never called. However, Bluetooth is enabled. What am I missing?
package com.example.bluetoothmaccounter;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import android.annotation.SuppressLint;
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.media.MediaPlayer;
import android.os.Bundle;
import android.os.Vibrator;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
Button buttonON , buttonOFF, scanBt;
ListView deviceList;
ArrayList<String> arrayList = new ArrayList<String>();
ArrayAdapter<String> arrayAdapter;
BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
int requestCodeForEnable = 1;
Intent btEnablingIntent;
Vibrator vibrator;
MediaPlayer mediaPlayer;
TextView textView2 ;
#Override
protected void onCreate (Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonOFF = findViewById(R.id.bt_off);
buttonON = findViewById(R.id.bt_on);
scanBt = findViewById(R.id.bt_scan);
deviceList = findViewById(R.id.device_list);
btEnablingIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
vibrator = (Vibrator) getSystemService(VIBRATOR_SERVICE);
mediaPlayer = MediaPlayer.create(this, R.raw.alarm);
textView2 = findViewById(R.id.textView2);
// /////////////////// Enable bluetooth ///////////////////////
buttonON.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (bluetoothAdapter == null) {
Toast.makeText(getApplicationContext(), "this device not support bluetooth", Toast.LENGTH_SHORT).show();
} else {
if (!bluetoothAdapter.isEnabled()) {
startActivityForResult(btEnablingIntent, requestCodeForEnable);
}
}
}
});
// /////////////////// disable bluetooth ///////////////////////
buttonOFF.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (bluetoothAdapter.isEnabled()) {
bluetoothAdapter.disable();
Toast.makeText(getApplicationContext(), "bluetooth disable", Toast.LENGTH_SHORT).show();
}
}
});
// /////////////////// start scan ///////////////////////
scanBt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
arrayList.clear();
if (!bluetoothAdapter.isEnabled()) {
Toast.makeText(getApplicationContext(), " bluetooth not Enabled", Toast.LENGTH_SHORT).show();
} else {
bluetoothAdapter.startDiscovery();
Toast.makeText(getApplicationContext(), "discover started", Toast.LENGTH_SHORT).show();
}
}
});
try {
IntentFilter intentFilter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
textView2.setText("befoore receiver");
registerReceiver(receiver, intentFilter);
arrayAdapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, arrayList);
deviceList.setAdapter(arrayAdapter);
} catch (Exception e) {
textView2.setText("exeption" + e.getMessage());
}
}
// Create a BroadcastReceiver for ACTION_FOUND.
private final BroadcastReceiver receiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
textView2.setText("on receive 1");
String action = intent.getAction();
if (BluetoothDevice.ACTION_FOUND.equals(action)) {
textView2.setText("found");
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
arrayList.add(device.getName() + device.getAddress());
String size = "size is " + arrayList.size();
textView2.setText(size);
arrayAdapter.notifyDataSetChanged();
if (arrayList.size() >= 1) {
Toast.makeText(getApplicationContext(), "There are :" + arrayList.size() + "person here ", Toast.LENGTH_LONG).show();
vibrator.vibrate(3 * 1000);
mediaPlayer.start();
}
//
}
}
};
#Override
protected void onDestroy () {
super.onDestroy();
// Don't forget to unregister the ACTION_FOUND receiver.
textView2.setText("destrrooooooy");
unregisterReceiver(receiver);
}
}

<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"></uses-permission>
<uses-permission android:name="android.permission.BLUETOOTH"></uses-permission>
You need to add these two permissions in AndroidManifest.xml

calling startActivityForResult isn't passing intents back properly

In my code, I have a class for a recipe and then another class for each step. The recipe class holds an arraylist of the steps in that recipe.
I have 3 processes being called one after the other:
MainActivity calls AddEditRecipe using startActivityResult
within AddEditRecipe I have another startActivityResult which calls AddStep
within AddStep I am adding a new instance of step to the list in the recipe.
It successfully adds the object to the list before finish() is called, but when I check the size of the list when I have gone to the 2nd activity it has reverted back to 0, even though I've managed to create buttons with the data I collected from the AddStep functions.
Basically I don't know what to do make it so it everything correctly persists.
Also a heads up, I am still fairly new too java so there's probably lots of other things wrong, any random advice is greatly appreciated.
MainActivity
import android.content.Intent;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.ScrollView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
Button newRecipe;
Button editRecipe;
Button deleteRecipe;
LinearLayout recipeLayout;
List<NewRecipe> listOfRecipes;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listOfRecipes = new ArrayList<>();
recipeLayout = (LinearLayout) findViewById(R.id.RecipeListLayout);
newRecipe = (Button) findViewById(R.id.NewRecipeButton);
newRecipe.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent i = new Intent(MainActivity.this, AddRecipePopUp.class);
startActivityForResult(i,998);
}
});
}
protected void onActivityResult(int requestCode, int resultCode, Intent data){
if(requestCode==999 && resultCode == RESULT_OK){
NewRecipe rec = (NewRecipe)data.getParcelableExtra("curr_recipe");
Log.d("Number of Steps",Integer.toString(rec.listOfSteps.size()));
UpdateScreen(rec);
}
if(requestCode== 998 && resultCode == RESULT_OK){
NewRecipe recipe =(NewRecipe)data.getParcelableExtra("curr_recipe");
listOfRecipes.add(recipe);
Intent i = new Intent(MainActivity.this,AddEditRecipe.class);
i.putExtra("curr_recipe", recipe);
startActivityForResult(i,999);
}
}
void UpdateScreen(final NewRecipe recipe){
Button button = new Button(this);
button.setText(recipe.name);
button.setHeight(120);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
NewRecipe recipe1 = recipe;
Button thisBut = (Button)view;
String butName = thisBut.getText().toString().toLowerCase();
for(int j = 0;j<listOfRecipes.size();j++){
String curr = listOfRecipes.get(j).name.toString().toLowerCase();
Log.d("Button ",thisBut.getText().toString());
Log.d("Current List ",listOfRecipes.get(j).name.toString().toLowerCase());
Log.d("Check bool statement", Boolean.toString(butName ==curr));
}
//recipe1 = listOfRecipes.get(0);
Intent i = new Intent(MainActivity.this, AddEditRecipe.class);
i.putExtra("curr_recipe",recipe1);
startActivityForResult(i,997);
}
});
LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
recipeLayout.addView(button,lp);
}
}
AddEditRecipe
import android.app.Activity;
import android.app.Dialog;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
public class AddEditRecipe extends Activity {
Button home;
Button add;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.add_edit_recipe);
Intent i = getIntent();
final NewRecipe this_recipe = i.getParcelableExtra("curr_recipe");
Log.d("Number of Steps",Integer.toString(this_recipe.listOfSteps.size()));
LinearLayout recipeLayout = (LinearLayout) findViewById(R.id.RecipeListLayout);
LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
for(int j = 0; j<this_recipe.listOfSteps.size();j++){
Button button = new Button(this);
button.setText(this_recipe.listOfSteps.get(j).processName);
button.setHeight(120);
recipeLayout.addView(button,lp);
}
home = (Button) findViewById(R.id.HomeButton);
home.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent i = new Intent(AddEditRecipe.this, MainActivity.class);
i.putExtra("curr_recipe", this_recipe);
setResult(RESULT_OK,i);
Log.d("Number of Steps",Integer.toString(this_recipe.listOfSteps.size()));
finish();
}
});
add = (Button) findViewById(R.id.AddStepButton);
add.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent i = new Intent(AddEditRecipe.this, AddStep.class);
i.putExtra("curr_recipe", this_recipe);
startActivityForResult(i,999);
}
});
}
protected void onActivityResult(int requestCode, int resultCode, Intent data){
if(requestCode==999 && resultCode == RESULT_OK){
NewRecipe curr_rec = (NewRecipe)data.getParcelableExtra("curr_recipe");
Button button = new Button(this);
button.setText(curr_rec.listOfSteps.get(curr_rec.listOfSteps.size()-1).processName + " " + curr_rec.listOfSteps.get(curr_rec.listOfSteps.size()-1).seconds );
button.setHeight(120);
LinearLayout lay = (LinearLayout) findViewById(R.id.RecipeListLayout) ;
LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
lay.addView(button,lp);
}
}
}
AddStep
import android.app.Activity;
import android.content.Intent;
import android.graphics.Canvas;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class AddStep extends Activity{
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.add_step);
Intent i = getIntent();
final NewRecipe this_recipe = (NewRecipe) i.getParcelableExtra("curr_recipe");
Button finish = (Button) findViewById(R.id.AddStepButton);
finish.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
EditText name = (EditText) findViewById(R.id.nameEditText);
EditText hours = (EditText) findViewById(R.id.HoursEditText);
EditText minutes = (EditText) findViewById(R.id.MinutesEditText);
EditText seconds = (EditText) findViewById(R.id.SecondsEditText);
this_recipe.AddStep((ConvertToSeconds(Integer.parseInt(hours.getText().toString()),Integer.parseInt(minutes.getText().toString()),Integer.parseInt(seconds.getText().toString()))),name.getText().toString());
Intent j = new Intent(AddStep.this, AddEditRecipe.class);
j.putExtra("curr_recipe", this_recipe);
Log.d("Number of Steps",Integer.toString(this_recipe.listOfSteps.size()));
setResult(RESULT_OK,j);
finish();
}
});
}
int ConvertToSeconds(int h, int m, int s){
int ans = 0;
for(int i = 0; i<h;i++){
ans+=3600;
}
for(int i = 0; i<m;i++){
ans+=60;
}
for(int i = 0; i<s;i++){
ans++;
}
return ans;
}
}

Code doesn't work

I'm trying to make an APK that saves passwords with the site using two different ArrayLists. This way, I can get the right indexnumber of the site and get the password based on this indexnumber. In the beginning of MainActivity, I add two random Strings to the ArrayLists, so that I don't have to work with empty ArrayLists, but this is utterly useless I think.
The problem is I can only view the last site-password I have put in. Previous combinations are "lost."
code:
MainActivity.java
package com.example.prive.passwordsafe;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
public ArrayList<String> passwordList = new ArrayList<>();
public ArrayList<String> siteList = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
passwordList.add("ejifjejfijeifjeijfiejifjeijfiejfijefie");
siteList.add("iejfijeifjiejfiejidvjijijeijivjiejvijeivjejv");
Button addButton = (Button) findViewById(R.id.addButton);
Button showButton = (Button) findViewById(R.id.showButton);
addButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
firstIntent();
}
});
showButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
secondIntent();
}
});
}
#Override
public void onResume(){
super.onResume();
add();
}
private void firstIntent() {
Intent intent = new Intent(MainActivity.this, addActivity.class);
intent.putStringArrayListExtra("passwordList", passwordList);
intent.putStringArrayListExtra("siteList", siteList);
startActivity(intent);
}
private void secondIntent() {
Intent intent = new Intent(MainActivity.this, showActivity.class);
intent.putStringArrayListExtra("passwordList", passwordList);
intent.putStringArrayListExtra("siteList", siteList);
startActivity(intent);
}
public void add(){
Bundle pickupData = getIntent().getExtras();
if(pickupData == null){
return;
}
String receivedPassword = pickupData.getString("Password");
String receivedSite;
receivedSite = pickupData.getString("Site");
passwordList.add(receivedPassword);
siteList.add(receivedSite);
}
}
addActivity.java
package com.example.prive.passwordsafe;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class addActivity extends AppCompatActivity {
public EditText siteInsert, passwordInsert;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_toevoeg);
siteInsert = (EditText) findViewById(R.id.siteInsert);
passwordInsert = (EditText) findViewById(R.id.passwordInsert);
siteInsert.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Toast msg = Toast.makeText(getBaseContext(), "site", Toast.LENGTH_LONG);
msg.show();
}
});
passwordInsert.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Toast msg = Toast.makeText(getBaseContext(), "password", Toast.LENGTH_LONG);
msg.show();
}
});
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
String password = passwordInsert.getText().toString();
String site = siteInsert.getText().toString();
Intent intent = new Intent(addActivity.this, MainActivity.class);
intent.putExtra("Password", password);
intent.putExtra("Site", site);
startActivity(intent);
}
});
}
}
showActivity.java
package com.example.prive.passwordsafe;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
public class showActivity extends AppCompatActivity {
public EditText editText;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_toon);
Button showButton = (Button) findViewById(R.id.showButton);
Button backButton = (Button) findViewById(R.id.backButton);
editText = (EditText) findViewById(R.id.editText);
final TextView textView = (TextView) findViewById(R.id.textView);
Bundle pickupData = getIntent().getExtras();
final ArrayList<String> passwordList = pickupData.getStringArrayList("passwordList");
final ArrayList<String> siteList = pickupData.getStringArrayList("siteList");
editText.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Toast msg = Toast.makeText(getBaseContext(), "site", Toast.LENGTH_LONG);
msg.show();
}
});
if (passwordenList != null && siteList != null) {
showButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
int numberOfPasswords = passwordenList.size();
for (int i = 0; i <= numberOfPasswords; i++) {
String password;
String temporary = editText.getText().toString();
if (temporary.equals(siteList.get(i))) {
password = passwordList.get(i);
textView.setText(password);
}else{
password = "wrong input";
textView.setText(password);
}
}
}
});
}else{
return;
}
backButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
finish();
}
});
}
}

When you exit an Activity, all the data on it is lost. You have to persist your ArrayList in SQLite or use SharedPreferences instead.
SharedPreferences: https://developer.android.com/reference/android/content/SharedPreferences.html
SQLite: https://developer.android.com/training/basics/data-storage/databases.html

java.lang.RuntimeException: Performing stop of activity that is not resumed:

I am getting a runtime exception when I am calling NavDrawerActivity from LoginScreen activity.
Error
java.lang.RuntimeException: Performing stop of activity that is not
resumed:
{com.example.owner.loginapp/com.example.owner.loginapp.NavDrawerActivity}
How to fix this error?
Here is my loginScreen code
package com.example.owner.loginapp;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;
import android.content.SharedPreferences;
public class LoginScreen extends AppCompatActivity {
ImageView image;
ImageView user_img;
ImageView pass_img;
Button log_in;
Button reg;
EditText editText_Username;
EditText editText_Pass;
UserSessionManager session;
private SharedPreferences sharedPreferences;
private static final String PREFER_NAME = "Reg";
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
session = new UserSessionManager(getApplicationContext());
image = (ImageView) findViewById(R.id.imageView);
image.setImageResource(R.drawable.smile);
user_img = (ImageView) findViewById(R.id.user_img);
user_img.setImageResource(R.drawable.user_img);
pass_img = (ImageView) findViewById(R.id.pass_img);
pass_img.setImageResource(R.drawable.img_pass);
log_in = (Button) findViewById(R.id.btn_Login);
reg = (Button) findViewById(R.id.btn_Reg);
editText_Username = (EditText) findViewById(R.id.editText_UserName);
editText_Pass = (EditText) findViewById(R.id.editText_Password);
Bitmap icon = BitmapFactory.decodeResource(getResources(),
image.setImageBitmap(icon);
Toast.makeText(getApplicationContext(),
"User Login Status: " + session.isUserLoggedIn(),
Toast.LENGTH_LONG).show();
sharedPreferences = getSharedPreferences(PREFER_NAME, Context.MODE_PRIVATE);
log_in.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String username = editText_Username.getText().toString();
String password = editText_Pass.getText().toString();
if (username.trim().length() > 0 && password.trim().length() > 0) {
String uName = null;
String uPassword = null;
if (sharedPreferences.contains("Name")) {
uName = sharedPreferences.getString("Name", "");
}
if (sharedPreferences.contains("Password")) {
uPassword = sharedPreferences.getString("Password", "");
}
if (username.equals(uName) && password.equals(uPassword)) {
session.createUserLoginSession(uName, uPassword);
Intent i = new Intent(getApplicationContext(), NavDrawerActivity.class);
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(i);
} else {
Toast.makeText(getApplicationContext(),
"Username/Password is incorrect",
Toast.LENGTH_LONG).show();
}
} else {
Toast.makeText(getApplicationContext(),
"Please enter username and password",
Toast.LENGTH_LONG).show();
}
}
});
reg.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
setContentView(R.layout.register);
Intent i = new Intent(getApplicationContext(), Reg.class);
startActivity(i);
}
});
}
}

I copied your code and tried to instantiate a Reg Activity class that I designed and everything worked fine. It is possible that you are doing something wrong in the 1onResumeoronCreate` of Reg class.
Post that class too for more information.

bluetooth pairing with selected device

Here is my problem/question, probably a nooby one....
I have an activity where the app checks if the bluetooth is switched on, if not it displays a pop-up window with a button to activate it.
when activated there is a button which will search for bluetooth devices.
now my question is how can i pair to the selected device which will be protected with an password, if it is already paired just connect to it (witouth entering the password again)
after connecting to the device it should go to the next page.
Here is my Code
package com.example.silcamanager96x32;
import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog;
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.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.Toast;
import android.view.View.OnClickListener;
import android.widget.AdapterView.OnItemClickListener;
public class Bluetooth_check extends Activity {
//global variables
private final static int REQUEST_ENABLE_BT = 1;
private ArrayAdapter<String> btArrayAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bluetooth_check);
btn_go();
btn_scan();
}
//tijdelijke button volgende pagina
public void btn_go(){
Button btn_go=(Button)findViewById(R.id.Button01);
btn_go.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
Log.i("clicks","You Clicked B1");
Intent i=new Intent(
Bluetooth_check.this,
home.class);
startActivity(i);
}
});
}
//button scannen naar bluetooth apparaten en in ene lijst plaatsen
public void btn_scan(){
final Button scanb = (Button)findViewById(R.id.button);
final ListView Deviceslist = (ListView)findViewById(R.id.listView1);
btArrayAdapter = new ArrayAdapter<String>(Bluetooth_check.this, android.R.layout.simple_list_item_1);
Deviceslist.setAdapter(btArrayAdapter);
//vraagt of app bluetooth mag inschakelen
final BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
if (mBluetoothAdapter == null) {
// Device does not support Bluetooth
Toast.makeText(Bluetooth_check.this, "Your device doesnot support Bluetooth", Toast.LENGTH_LONG).show();
}
if (!mBluetoothAdapter.isEnabled()) {
Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}
//onclick scan button
scanb.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
btArrayAdapter.clear();
mBluetoothAdapter.startDiscovery();
Toast.makeText(Bluetooth_check.this, "Scanning Devices", Toast.LENGTH_LONG).show();
}
});
Deviceslist.setOnItemClickListener( new OnItemClickListener() {
public void onItemClick(AdapterView<?> arg0, View v, int position,
long id) {
// onclick item gevonden apparaten
AlertDialog.Builder adb = new AlertDialog.Builder(
Bluetooth_check.this);
adb.setTitle("ListView OnClick");
adb.setMessage("Selected Item is = "
+ Deviceslist.getItemAtPosition(position));
adb.setPositiveButton("Ok", null);
adb.show();
}
});
registerReceiver(FoundReceiver, new IntentFilter(BluetoothDevice.ACTION_FOUND));
}
#Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
unregisterReceiver(FoundReceiver);
}
private final BroadcastReceiver FoundReceiver = new BroadcastReceiver(){
#Override
public void onReceive(Context context, Intent intent) {
// TODO Auto-generated method stub
String action = intent.getAction();
if(BluetoothDevice.ACTION_FOUND.equals(action)) {
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
btArrayAdapter.add(device.getName() + "\n" + device.getAddress());
btArrayAdapter.notifyDataSetChanged();
}
}};
}

try this link here is whole code ...Android + Pair devices via bluetooth programmatically and add permission to manifest
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.BLUETOOTH" />