Develop Reference

ListView.setAdapter(ArrayAdapter) is crashing app

I am trying to populate a listView with paired bluetooth devices. I tried doing so with a ListView in my MainActivity and it worked perfectly. However, when I tried it with a ListView in a different activity it crashed the app. I basically want to populate a ListView in a pop-up dialog box.
Here is the code:
activity_device_list.xml (MainActivity)
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:weightSum="1">
<ListView
android:id="#+id/listDevicesMain"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
device_dialog.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="#+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="0.12"
android:gravity="center"
android:paddingBottom="10dp"
android:paddingTop="10dp"
android:text="Paired Devices"
android:textSize="25sp" />
<ListView
android:id="#+id/listDevicesDialog"
android:layout_width="match_parent"
android:layout_height="395dp"
android:layout_weight="0.38" />
</LinearLayout>
DeviceList.java
package example.btmodule;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.Set;
import static example.btmodule.R.layout.activity_device_list;
public class DeviceList extends AppCompatActivity {
ListView devicelist;
private BluetoothAdapter myBluetooth = null;
private Set<BluetoothDevice> pairedDevices;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(activity_device_list);
myBluetooth = BluetoothAdapter.getDefaultAdapter();
if(myBluetooth == null)
{
//Show a mensag. that thedevice has no bluetooth adapter
Toast.makeText(getApplicationContext(), R.string.bluetooth_unavailable, Toast.LENGTH_LONG).show();
//finish apk
finish();
}
else {
if (myBluetooth.isEnabled()) {
} else {
//Ask to the user turn the bluetooth on
Intent turnBTon = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(turnBTon, 1);
}
}
}
private void pairedDevicesList()
{
pairedDevices = myBluetooth.getBondedDevices();
ArrayList list = new ArrayList();
devicelist = (ListView)findViewById(R.id.listDevicesDialog);
if (pairedDevices.size()>0)
{
for(BluetoothDevice bt : pairedDevices)
{
list.add(bt.getName() + "\n" + bt.getAddress()); //Get the device's name and the address
}
}
else
{
Toast.makeText(getApplicationContext(), R.string.no_devices_found, Toast.LENGTH_LONG).show();
}
final ArrayAdapter adapter = new ArrayAdapter(this,android.R.layout.simple_list_item_1, list);
devicelist.setAdapter(adapter);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
// menu item selection
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle item selection
switch (item.getItemId()) {
case R.id.action_connect:
showDialog();
pairedDevicesList();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
// show the dialog for connected devices
private void showDialog(){
AlertDialog.Builder mBuilder = new AlertDialog.Builder(DeviceList.this);
View mView = getLayoutInflater().inflate(R.layout.device_dialog, null);
mBuilder.setView(mView);
AlertDialog dialog = mBuilder.create();
dialog.show();
}
}
If I change devicelist to R.id.listDevicesMain the code works perfectly fine.

you calling the wrong list view the id of the list view as you have given is
<ListView
android:id="#+id/listDevicesMain"
android:layout_width="match_parent"
android:layout_height="match_parent" />
and you are trying to call the listview with id
devicelist = (ListView)findViewById(R.id.listDevicesDialog);
hope this will solve the issue.

devicelist = (ListView)findViewById(R.id.listDevicesDialog); - here you are looking for listDevicesDialog in activity layout, so devicesList becomes null. You should add devicelist = (ListView) mView.findViewById(R.id.listDevicesDialog); to showDialog() method and bring there rest of the operations related with searching for paired devices and setting adapter.
You can also call pairedDevicesList from showDialog and pass view where listDevicesDialog is:
private void pairedDevicesList(View dialogView)
{
pairedDevices = myBluetooth.getBondedDevices();
ArrayList list = new ArrayList();
devicelist = (ListView) dialogView.findViewById(R.id.listDevicesDialog);
...
}
// show the dialog for connected devices
private void showDialog()
{
AlertDialog.Builder mBuilder = new AlertDialog.Builder(DeviceList.this);
View mView = getLayoutInflater().inflate(R.layout.device_dialog, null);
mBuilder.setView(mView);
AlertDialog dialog = mBuilder.create();
dialog.show();
pairedDevicesList(mView);
}

IllegalStateException: Could not find method in a parent or ancestor Context for android:onClick attribute defined on view class

When i click on a button with ID "btnDiscoverable_on_off" and "lvNewDevices" i get this error :
java.lang.IllegalStateException: Could not find method btnDiscover(View) in a parent or ancestor Context for android:onClick attribute defined on view class android.support.v7.widget.AppCompatButton with id 'btnFindUnpairedDevices'
This is the code :
import android.Manifest;
import android.app.Fragment;
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.Build;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.ListView;
import java.util.ArrayList;
public class PrimoFragment extends Fragment implements
AdapterView.OnItemClickListener {
View myView;
private static final String TAG = "MainActivity";
BluetoothAdapter mBluetoothAdapter;
Button btnEnableDisable_Discoverable;
public ArrayList<BluetoothDevice> mBTDevices = new ArrayList<>();
public DeviceListAdapter mDeviceListAdapter;
ListView lvNewDevices;
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, Bundle savedInstanceState) {
myView = inflater.inflate(R.layout.primo_layout, container, false);
Button btnONOFF = (Button) myView.findViewById(R.id.btnONOFF);
btnEnableDisable_Discoverable = (Button) myView.findViewById(R.id.btnDiscoverable_on_off);
lvNewDevices = (ListView) myView.findViewById(R.id.lvNewDevices);
mBTDevices = new ArrayList<>();
//Broadcasts when bond state changes (ie:pairing)
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_BOND_STATE_CHANGED);
getActivity().registerReceiver(mBroadcastReceiver4, filter);
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
lvNewDevices.setOnItemClickListener(PrimoFragment.this);
btnONOFF.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Log.d(TAG, "onClick: enabling/disabling bluetooth.");
enableDisableBT();
}
});
return myView;
}
public void enableDisableBT(){
if(mBluetoothAdapter == null){
Log.d(TAG, "enableDisableBT: Does not have BT capabilities.");
}
if(!mBluetoothAdapter.isEnabled()){
Log.d(TAG, "enableDisableBT: enabling BT.");
Intent enableBTIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivity(enableBTIntent);
IntentFilter BTIntent = new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED);
getActivity().registerReceiver(mBroadcastReceiver1, BTIntent);
}
if(mBluetoothAdapter.isEnabled()){
Log.d(TAG, "enableDisableBT: disabling BT.");
mBluetoothAdapter.disable();
IntentFilter BTIntent = new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED);
getActivity().registerReceiver(mBroadcastReceiver1, BTIntent);
}
}
public void btnEnableDisable_Discoverable(View view) {
Log.d(TAG, "btnEnableDisable_Discoverable: Making device discoverable for 300 seconds.");
Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300);
startActivity(discoverableIntent);
IntentFilter intentFilter = new IntentFilter(mBluetoothAdapter.ACTION_SCAN_MODE_CHANGED);
getActivity().registerReceiver(mBroadcastReceiver2,intentFilter);
}
public void btnDiscover(View view) {
Log.d(TAG, "btnDiscover: Looking for unpaired devices.");
if(mBluetoothAdapter.isDiscovering()){
mBluetoothAdapter.cancelDiscovery();
Log.d(TAG, "btnDiscover: Canceling discovery.");
//check BT permissions in manifest
checkBTPermissions();
mBluetoothAdapter.startDiscovery();
IntentFilter discoverDevicesIntent = new IntentFilter(BluetoothDevice.ACTION_FOUND);
getActivity().registerReceiver(mBroadcastReceiver3, discoverDevicesIntent);
}
if(!mBluetoothAdapter.isDiscovering()){
//check BT permissions in manifest
checkBTPermissions();
mBluetoothAdapter.startDiscovery();
IntentFilter discoverDevicesIntent = new IntentFilter(BluetoothDevice.ACTION_FOUND);
getActivity().registerReceiver(mBroadcastReceiver3, discoverDevicesIntent);
}
}
/**
* This method is required for all devices running API23+
* Android must programmatically check the permissions for bluetooth. Putting the proper permissions
* in the manifest is not enough.
*
* NOTE: This will only execute on versions > LOLLIPOP because it is not needed otherwise.
*/
private void checkBTPermissions() {
if(Build.VERSION.SDK_INT > Build.VERSION_CODES.LOLLIPOP){
int permissionCheck = this.getActivity().checkSelfPermission("Manifest.permission.ACCESS_FINE_LOCATION");
permissionCheck += this.getActivity().checkSelfPermission("Manifest.permission.ACCESS_COARSE_LOCATION");
if (permissionCheck != 0) {
this.getActivity().requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION}, 1001); //Any number
}
}else{
Log.d(TAG, "checkBTPermissions: No need to check permissions. SDK version < LOLLIPOP.");
}
}
#Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
//first cancel discovery because its very memory intensive.
mBluetoothAdapter.cancelDiscovery();
Log.d(TAG, "onItemClick: You Clicked on a device.");
String deviceName = mBTDevices.get(i).getName();
String deviceAddress = mBTDevices.get(i).getAddress();
Log.d(TAG, "onItemClick: deviceName = " + deviceName);
Log.d(TAG, "onItemClick: deviceAddress = " + deviceAddress);
//create the bond.
//NOTE: Requires API 17+? I think this is JellyBean
if(Build.VERSION.SDK_INT > Build.VERSION_CODES.JELLY_BEAN_MR2){
Log.d(TAG, "Trying to pair with " + deviceName);
mBTDevices.get(i).createBond();
}
}
}
XML code primo_fragment:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent" android:layout_height="match_parent">
<Button
android:text="ON/OFF"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/btnONOFF"
android:layout_alignParentEnd="true" />
<Button
android:text="Enable Discoverable"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/btnDiscoverable_on_off"
android:onClick="btnEnableDisable_Discoverable"
android:layout_centerHorizontal="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/btnFindUnpairedDevices"
android:text="Discover"
android:onClick="btnDiscover" />
<ListView
android:layout_width="wrap_content"
android:layout_height="150dp"
android:id="#+id/lvNewDevices"
android:layout_marginTop="62dp"
android:layout_alignParentStart="true" />
</RelativeLayout>
device_adapter_view
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/tvDeviceName"
android:textSize="15sp"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/tvDeviceAddress"
android:textSize="15sp"/>
</LinearLayout>
What is wrong with these two button ? I can't find the problem

Please follow this structure to use xml onClick attribute for Fragment. Hope your problem will be resolved.

in this program passing ArrayList from one activity to another not working

first activity:
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
private Button bt1;
private Button bt2;
private EditText ed1;
private EditText ed2;
private TextView tv3;
static ArrayList<String> s = new ArrayList<>();
static ArrayList<Integer> i = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bt1 = (Button)findViewById(R.id.button);
ed1 = (EditText) findViewById(R.id.editText);
ed2 = (EditText)findViewById(R.id.editText2);
bt2 = (Button)findViewById(R.id.button2);
tv3 = (TextView)findViewById(R.id.textView3);
bt2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
s.add(ed1.getText().toString());
i.add(Integer.parseInt(ed2.getText().toString()));
}
});
bt1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
try {
Intent intent = new Intent(MainActivity.this, second.class);
intent.putExtra("key", s);
startActivity(intent);
}
catch(Exception e) {
tv3.setText(e.getMessage());
}
}
});
}
}
Second activity:
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.MotionEvent;
import android.widget.TextView;
import java.util.ArrayList;
public class second extends AppCompatActivity {
private TextView tv1;
private TextView tv2;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.second);
tv1 = (TextView)findViewById(R.id.textView);
tv2 = (TextView)findViewById(R.id.textView2);
ArrayList<String> s = (ArrayList<String>)getIntent().getSerializableExtra("key");
for(int j=0;j<=s.size();j++) {
tv1.setText(s.get(j));
}
}
}
I don't understand the problem in this code. when I click on bt2 to pass the ArrayList from on activity to another then the app just shutdown. I am not able to understand the problem in this code.
Please help me,
I have also updated the manifest.xml for second class.

Are you sure
i.add(Integer.parseInt(ed2.getText().toString()));
in the onClick() call doesnt throw an Exception?
Use a try-catch block around your code in Listener.onClick().
Btw., you can easily use Lambda Exrpessions for ActionListeners.
https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html

Please use following construct:-
While Sending:
intent.putStringArrayListExtra("key", s)
While Receiving:
ArrayList<String> s = getIntent().getStringArrayListExtra("key");

Replace your for loop with below, use j< s.size and not j<=s.size
for(int j=0;j<s.size();j++)
{
tv1.setText(s.get(j));
}

You can do like this :
Bundle info= new Bundle();
ArrayList<Product> mas = new ArrayList<Product>();
info.putSerializable("product", mas);
intent.putExtras(info);
And get the values with this:
ArrayList<Product> prod = getIntent().getSerializableExtra(key);
Product class like a serializable object
private class Product implements Serializable {
}
Here it is just how you can pass arraylist between activities.Hope you wil get an idea to solve your issues.

intent.putExtra("key", s);-- this is wrong, you are sending a string but not your arrayList
Try sending with-- intent.putStringArrayListExtra("key", s);
and receiving -- ArrayList<String> stringArray = getIntent().getStringArrayListExtra("key");
hope this will solve your problem...

In your second activity onCreate, add the following code:
#Override public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.second);
// Add view
// Must add check extras if null.
Bundle extras = getIntent().getExtras();
ArrayList<String> s = extras.getStringArrayListExtra("key");
// do something
}
In your first activity, send intent with:
Intent intent = new Intent(MainActivity.this, second.class);
intent.putStringArrayListExtra("key", s);
startActivity(intent);

I've tried an sample app with your code. Hope this will help you.
Kindly check my codes.
First Activity
package com.arindam.testapp;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.util.ArrayList;
public class FirstActivity extends AppCompatActivity {
Button bt1;
EditText ed1;
EditText ed2;
TextView tv3;
ArrayList<String> s = new ArrayList<>();
ArrayList<String> i = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_first);
bt1 = (Button)findViewById(R.id.button);
ed1 = (EditText) findViewById(R.id.editText);
ed2 = (EditText)findViewById(R.id.editText2);
tv3 = (TextView)findViewById(R.id.textView);
bt1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
try {
s.add(ed1.getText().toString());
i.add(ed2.getText().toString());
Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
intent.putExtra("key", s);
intent.putExtra("value", i);
startActivity(intent);
}
catch(Exception e)
{
tv3.setText(e.getMessage());
}
}
});
}
}
First Activity Layout
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:background="#679667"
android:orientation="vertical"
tools:context="com.arindam.testapp.FirstActivity">
<EditText
android:id="#+id/editText"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<EditText
android:id="#+id/editText2"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Add"/>
<TextView
android:id="#+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dp" />
</LinearLayout>
Second Activity
package com.arindam.testapp;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.TextView;
import java.util.ArrayList;
public class SecondActivity extends AppCompatActivity {
private TextView tv1;
private TextView tv2;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
tv1 = (TextView)findViewById(R.id.textView);
tv2 = (TextView)findViewById(R.id.textView2);
ArrayList<String> s = getIntent().getStringArrayListExtra("key");
for(int j=0;j<s.size();j++)
{
tv1.setText(s.get(j));
}
ArrayList<String> i = getIntent().getStringArrayListExtra("value");
for(int k=0;k<i.size();k++)
{
tv2.setText(i.get(k));
}
}
}
Second Activity Layout
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:background="#229597"
android:orientation="vertical"
tools:context="com.arindam.testapp.SecondActivity">
<TextView
android:id="#+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp" />
<TextView
android:id="#+id/textView2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"/>
</LinearLayout>
If you want to work with key value pairs, go for hashMap.

Android dynamic listview

I want to make a ListView that gets its elements(strings) from user input. I have a button that directs the user to another activity and while in it, the user enters a name and presses another button to come back to the original activity. The same button gets and adds a string to the ArrayAdapter that the ListView uses and displays it as an element in the ListView. It doesn't seem to work and I know it's a stupid mistake, but I'm fresh to android development and this in particular I haven't done before.
Here's all the code:
the MainActivity
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import java.util.ArrayList;
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ArrayList<String> simpleArray =new ArrayList<String>();
ListAdapter simpleAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,
simpleArray);
ListView lv = (ListView) findViewById(R.id.lv);
lv.setAdapter(simpleAdapter);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void enterActivity(View view) {
Intent toEnterSecond = new Intent(this, SecondActivity.class);
startActivity(toEnterSecond);
}
}
The second acitivity
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import java.util.ArrayList;
public class SecondActivity extends Activity{
private EditText projectName;
ArrayList simpleArray;
ArrayAdapter simpleAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.second);
projectName = (EditText) findViewById(R.id.eTxt);
}
public void getBack(View view) {
String projectCalling = String.valueOf(projectName.getText());
simpleArray.add(projectCalling);
simpleAdapter.notifyDataSetChanged();
Intent comeBack = new Intent(this, MainActivity.class);
startActivity(comeBack);
}
}
And the layouts
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<Button
android:layout_width="match_parent"
android:layout_height="80dp"
android:id="#+id/simpleButton"
android:text="click me plox"
android:onClick="enterActivity"/>
<ListView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/simpleButton"
android:id="#+id/lv">
</ListView>
</RelativeLayout>
//
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="20dp"
android:text="Enter the name of your project:"
android:id="#+id/txt"/>
<EditText
android:layout_width="200dp"
android:layout_height="40dp"
android:layout_below="#+id/txt"
android:id="#+id/eTxt"/>
<Button
android:layout_width="100dp"
android:layout_height="60dp"
android:layout_below="#+id/eTxt"
android:text="click"
android:onClick="getBack"/>
</RelativeLayout>

Explanation:
You can start SecondActivity with startActivityForResult() instead of startActivity as answered here and in onResultActivity method you can call simpleAdapter.notifyDataSetChanged();. Don't call simpleAdapter.notifyDataSetChanged(); in SecondActivity.
To learn how to use startActivityForResult check this.
Also use finish() instead of
Intent comeBack = new Intent(this, MainActivity.class);
startActivity(comeBack);
in SecondActivity to go back to MainActivity.
Solution:
Change MainActivity enterActivity method to this:
...
public void enterActivity(View view) {
Intent toEnterSecond = new Intent(this, SecondActivity.class);
startActivityForResult(toEnterSecond,1);
}
Add this to end of SecondActivity getBack method:
MainActivity.simpleArray.add(projectCalling);
Intent returnIntent = new Intent();
setResult(RESULT_OK,returnIntent);
finish();
Finally add this new method to MainActivity:
protected void onActivityResult(int requestCode, int resultCode, Intent data{
if (requestCode == 1) {
if(resultCode == RESULT_OK){
((ArrayAdapter) simpleAdapter).notifyDataSetChanged();
}
}
}
To be able to access simpleAdapter, you need to define it outside of onCreate:
public class MainActivity extends ActionBarActivity {
private ListAdapter simpleAdapter;
public static ArrayList<String> simpleArray;
#Override
protected void onCreate(Bundle savedInstanceState) {
...
simpleArray =new ArrayList<String>();
simpleAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,
simpleArray);
...
}

Why is my Bluetooth application Crashing

I am working on a bluetooth application but my application crash .Here is my MainActivity.java
package com.race_gurram.bluetoothadapter;
import java.util.ArrayList;
import java.util.Set;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;
public class MainActivity extends Activity {
private Button on, off, get, bring;
private BluetoothAdapter BA;
private Set<BluetoothDevice> pairedDevices;
private ListView lv;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
on = (Button) findViewById(R.id.on);
off = (Button) findViewById(R.id.off);
get = (Button) findViewById(R.id.get);
bring = (Button) findViewById(R.id.list);
lv = (ListView) findViewById(R.id.listView1);
BA = BluetoothAdapter.getDefaultAdapter();
}
public void on(View view)
{
if(!BA.isEnabled())
{
Intent turnOn = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(turnOn,0);
Toast.makeText(getApplicationContext(), "Turned On", Toast.LENGTH_SHORT).show();
}
else
{
Toast.makeText(getApplicationContext(), "Already on", Toast.LENGTH_SHORT).show();
}
}
public void list(View view)
{
pairedDevices = BA.getBondedDevices();
ArrayList list = new ArrayList();
for(BluetoothDevice bt : pairedDevices)
list.add(BA.getName());
Toast.makeText(getApplicationContext(), "Searching for devices", Toast.LENGTH_SHORT).show();
final ArrayAdapter adapter = new ArrayAdapter(this,android.R.layout.simple_list_item_1,list);
lv.setAdapter(adapter);
}
public void get()
{
Intent getVisible = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
startActivityForResult(getVisible,0);
}
public void off()
{
BA.disable();
Toast.makeText(getApplicationContext(), "Turned off", Toast.LENGTH_SHORT).show();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
and this is my activity.xml file
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<ScrollView
android:id="#+id/scrollView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<Button
android:id="#+id/on"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="on"
android:text="#string/on" />
<Button
android:id="#+id/get"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="get"
android:text="#string/get" />
<Button
android:id="#+id/list"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="list"
android:text="#string/bring" />
<Button
android:id="#+id/off"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="off"
android:text="#string/off" />
<ListView
android:id="#+id/listView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:visibility="visible" >
</ListView>
</LinearLayout>
</ScrollView>
</RelativeLayout>
Whenever I onclick on a button the application crashes... Please help me out with this .. thank in advance.

On get and off method, there should be a View parameter, right?
public void get(View v) {
Intent getVisible = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
startActivityForResult(getVisible,0);
} public void off(View v) {
BA.disable();
Toast.makeText(getApplicationContext(), "Turned off", Toast.LENGTH_SHORT).show(); }

Perhaps it is when you click the list button. Assuming that the phone has 0 bonded devices,
paired.getBondedDevices() will probably return null and the program crashes due to a NullPointerException.
pairedDevices = BA.getBondedDevices();
ArrayList list = new ArrayList();
if(pairedDevices != null) {
for(BluetoothDevice bt : pairedDevices)
list.add(BA.getName());
}