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Send a string through WiFi-Direct between two android devices

It is now over a month that I'm trying to send a string using WiFi-Direct between two android devices, but I'm still struggling hard to understand what I'm doing wrong.
I've looked around forums but they often don't give much detail on how to achieve what I want.
I also went through those two guides from the android developer's website:
Create P2P connections with Wi-Fi Direct
Wi-Fi Direct (peer-to-peer or P2P) overview
I'm using one activity - ActivityConnection - where I toggle the visibility of views depending on whether the user previously chose to send or to receive the string.
Immediatly, on the client side, discoverPeers() looks for any device with WiFi-Direct turned on and displays them on a ListView. Once the user chooses a device and presses the send button, the connection makes itself and the string is sent.
On the server side, the server is immediatly launched using my AsyncServerTask class. There, it waits for a client to connect and to retrieve its sent string.
My main problem is that, after choosing the device and tapping on the send button, the server side isn't receiving anything.
My second problem is that, sometimes, devices aren't being discovered and the listview stays empty.
Am I missing something? Or maybe doing something wrong?
Here's my current code.
I took the liberty to get rid of any line I thought to be out of context to make it easier to read.
ActivityConnection
public class ActivityConnection extends AppCompatActivity implements NewPeersListener {
public static final String CONNECTION_ACTOR = "actor";
public static final String SEND_INFO = "send";
public static final String RECEIVE_INFO = "receive";
ListView listViewDevices;
private IntentFilter intentFilter;
private WifiP2pManager manager;
private WifiP2pManager.Channel channel;
private WiFiDirectBroadcastReceiver receiver;
public List <WifiP2pDevice> listDevices;
private WifiP2pDevice selectedDevice;
#Override
public void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
confirm.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
connectToSelectedDevice();
}
});
Intent intent = this.getIntent();
String actor = intent.getStringExtra(CONNECTION_ACTOR);
this.intentFilter = new IntentFilter();
this.intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);
this.intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);
this.intentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);
this.intentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);
this.manager = (WifiP2pManager) this.getSystemService(Context.WIFI_P2P_SERVICE);
this.channel = this.manager.initialize(this, this.getMainLooper(), null);
this.receiver = new WiFiDirectBroadcastReceiver(this.manager, this.channel, this);
this.listDevices = new ArrayList <> ();
if (actor.equals(SEND_INFO)) {
DeviceAdapter adapter = new DeviceAdapter(ActivityConnection.this, R.layout.device_item, this.listDevices);
this.listViewDevices.setAdapter(adapter);
this.listViewDevices.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
selectedDevice = listDevices.get(position);
}
});
this.discoverPeers();
}
else if (actor.equals(RECEIVE_INFO)) {
new ServerAsyncTask(this).execute();
}
}
#Override
protected void onResume() {
super.onResume();
this.receiver = new WiFiDirectBroadcastReceiver(this.manager, this.channel, this);
this.registerReceiver(this.receiver, this.intentFilter);
}
#Override
protected void onPause() {
super.onPause();
this.unregisterReceiver(this.receiver);
}
public void resultReceived (String result) {
Toast.makeText(ActivityConnection.this, "Received! :)", Toast.LENGTH_SHORT).show();
}
private void discoverPeers () {
manager.discoverPeers(channel, new WifiP2pManager.ActionListener() {
#Override
public void onSuccess() {
// The discovery process succeeded
}
#Override
public void onFailure(int reason) {
// The discovery process DID NOT succeed
Toast.makeText(ActivityConnection.this, "Discovery process DID NOT succeed. Please verify that WiFi-Direct is active.", Toast.LENGTH_LONG).show();
}
});
}
private void connectToSelectedDevice () {
WifiP2pConfig config = new WifiP2pConfig();
config.deviceAddress = this.selectedDevice.deviceAddress;
this.manager.connect(this.channel, config, new WifiP2pManager.ActionListener() {
#Override
public void onSuccess() {
// Send string
Intent serviceIntent = new Intent(ActivityConnection.this, TransferService.class);
serviceIntent.setAction(TransferService.ACTION_SEND_STRING);
serviceIntent.putExtra(TransferService.EXTRAS_GROUP_OWNER_ADDRESS, getMacAddress());
serviceIntent.putExtra(TransferService.EXTRAS_GROUP_OWNER_PORT, 8090);
startService(serviceIntent);
onBackPressed();
}
#Override
public void onFailure(int reason) {
Toast.makeText(ActivityConnection.this, "Connection failed. Try again.", Toast.LENGTH_SHORT).show();
}
});
}
#NonNull
private String getMacAddress () {
try {
List <NetworkInterface> all = Collections.list(NetworkInterface.getNetworkInterfaces());
for (NetworkInterface nif : all) {
if (!nif.getName().equalsIgnoreCase("wlan0")) continue;
byte[] macBytes = nif.getHardwareAddress();
if (macBytes == null) {
return "";
}
StringBuilder result = new StringBuilder();
for (byte b : macBytes) {
result.append(String.format("%02X:",b));
}
if (result.length() > 0) {
result.deleteCharAt(result.length() - 1);
}
return result.toString();
}
} catch (Exception e) {
}
return "02:00:00:00:00:00";
}
#Override
public void newPeers (WifiP2pDeviceList wifiP2pDeviceList) {
this.listDevices = new ArrayList <> (wifiP2pDeviceList.getDeviceList());
DeviceAdapter adapter = new DeviceAdapter(ActivityConnection.this, R.layout.device_item, this.listDevices);
this.listViewDevices.setAdapter(adapter);
}
}
WiFiDirectBroadcastReceiver
public class WiFiDirectBroadcastReceiver extends BroadcastReceiver {
private WifiP2pManager manager;
private WifiP2pManager.Channel channel;
private ActivityConnection activity;
private List <NewPeersListener> listeners;
public WiFiDirectBroadcastReceiver(WifiP2pManager manager, WifiP2pManager.Channel channel, ActivityConnection activity) {
super();
this.manager = manager;
this.channel = channel;
this.activity = activity;
this.listeners = new ArrayList <> ();
this.listeners.add(activity);
}
#Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) {
int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1);
if (state == WifiP2pManager.WIFI_P2P_STATE_ENABLED) {
// Wi-Fi P2P is enabled
} else {
// Wi-Fi P2P is not enabled
Toast.makeText(this.activity, "Please turn on WiFi-Direct (or WiFi-P2P).", Toast.LENGTH_SHORT).show();
}
} else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {
// Request available peers from the wifi p2p manager.
if (this.manager != null) {
this.manager.requestPeers(this.channel, new WifiP2pManager.PeerListListener() {
#Override
public void onPeersAvailable(WifiP2pDeviceList peers) {
for (NewPeersListener listener : listeners) {
listener.newPeers(peers);
}
}
});
}
} else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {
// Respond to new connection or disconnections
} else if (WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)) {
// Respond to this device's wifi state changing
}
}
}
ServerAsyncTask (server)
public class ServerAsyncTask extends AsyncTask<Void, Void, String> {
private ServerSocket serverSocket;
private Socket clientSocket;
private DataInputStream stream;
private WeakReference <Context> contextWeakReference;
ServerAsyncTask (Context context) {
this.contextWeakReference = new WeakReference <> (context);
}
#Override
protected String doInBackground (Void... params) {
try {
this.serverSocket = new ServerSocket(8090);
this.clientSocket = this.serverSocket.accept();
this.stream = new DataInputStream(this.clientSocket.getInputStream());
String received = this.stream.readUTF();
this.serverSocket.close();
return received;
} catch (IOException e) {
Log.e(TransferService.TAG, Objects.requireNonNull(e.getMessage()));
return null;
} finally {
if (this.stream != null) {
try {
this.stream.close();
} catch (IOException e) {
Log.e(TransferService.TAG, Objects.requireNonNull(e.getMessage()));
}
}
if (this.clientSocket != null) {
try {
this.clientSocket.close();
} catch (IOException e) {
Log.e(TransferService.TAG, Objects.requireNonNull(e.getMessage()));
}
}
if (this.serverSocket != null) {
try {
this.serverSocket.close();
} catch (IOException e) {
Log.e(TransferService.TAG, Objects.requireNonNull(e.getMessage()));
}
}
}
}
/*
* (non-Javadoc)
* #see android.os.AsyncTask#onPostExecute(java.lang.Object)
*/
#Override
protected void onPostExecute (String result) {
super.onPostExecute(result);
((ActivityConnection) this.contextWeakReference.get()).resultReceived(result);
}
}
TransferService (client)
public class TransferService extends IntentService {
public static final String TAG = "WIFI_DIRECT";
private static final int SOCKET_TIMEOUT = 5000;
public static final String ACTION_SEND_STRING = "sendString";
public static final String EXTRAS_GROUP_OWNER_ADDRESS = "go_host";
public static final String EXTRAS_GROUP_OWNER_PORT = "go_port";
public TransferService (String name) {
super(name);
}
public TransferService () {
super("TransferService");
}
#Override
protected void onHandleIntent (Intent intent) {
Context context = getApplicationContext();
if (intent.getAction().equals(ACTION_SEND_STRING)) {
String toSend = "string to send";
String host = intent.getExtras().getString(EXTRAS_GROUP_OWNER_ADDRESS);
int port = intent.getExtras().getInt(EXTRAS_GROUP_OWNER_PORT);
Socket socket = null;
DataOutputStream stream = null;
try {
// Create a client socket with the host, port, and timeout information.
socket = new Socket();
socket.bind(null);
socket.connect((new InetSocketAddress(host, port)), SOCKET_TIMEOUT);
Log.d(TAG, "Client connected socket - " + socket.isConnected());
// Send string
stream = new DataOutputStream(socket.getOutputStream());
stream.writeUTF(toSend);
stream.close();
Toast.makeText(context, "Sent! :)", Toast.LENGTH_SHORT).show();
} catch (IOException e) {
Log.e(TAG, Objects.requireNonNull(e.getMessage()));
} finally {
if (stream != null) {
try {
stream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (socket != null) {
if (socket.isConnected()) {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
}
}

In the ActivityConnetion class, I was giving a MAC address instead of an IP address. I don't know why I didn't see this, nor why I did it in the first place. So I looked around this forum and found out how to get the IP address of the WiFi-Direct's group owner: Wifi Direct Group Owner Address .
To get the code running, I went into the ActivityConnetion class, delete the getMacAddress() method and replaced this line:
serviceIntent.putExtra(TransferService.EXTRAS_GROUP_OWNER_ADDRESS, getMacAddress());
with this line:
serviceIntent.putExtra(TransferService.EXTRAS_GROUP_OWNER_ADDRESS, "192.168.49.1");
As the group owner's IP is always the same, one can write it down directly. As doing so can stop working if the IP changes, I would recommend looking for the group owner's IP instead. The link above show's how to do it.

Two ACR122U NFC readers on Raspberry Pi3 Android

I'm trying to work with two NFC ACR122u readers connected to my Raspberry Pi3 under Android IoT.
I'm utilizing native acssmc-1.1.3.jar library provided by ASC.
Everything is working fine with one reader connected, I'm able to get tagId, turn on/off buzzer/light, but I'm unable to communicate with second reader when both are connected.
So, I'm able to power on both of them, initialize BroadcastReceiver, but when it comes to reader state change listener onCreate method from Reader class in debugger log I see that one reader was closed with message D/UsbDeviceConnectionJNI: close.
The code below initialize and power on both readers. But can't get reader state for both readers, only for one of them 'cause one will be closed right after initialization.
I thought that I have to initialize Reader class for each reader individually, but have no luck with this try as well.
I'm lost at this part. Any help would be really appreciated!
public class MainActivity extends AppCompatActivity {
private static final String ACTION_USB_PERMISSION = "com.android.reader.USB_PERMISSION";
private List<UsbDevice> active_devices = new ArrayList<>(2);
private PendingIntent mPermissionIntent;
private Reader mReader;
private UsbManager mManager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mManager = (UsbManager) getSystemService(Context.USB_SERVICE);
Map<String, UsbDevice> connectedDevices = mManager.getDeviceList();
mReader = new Reader(mManager);
int i = 0;
for (UsbDevice device : connectedDevices.values()) {
if (mReader.isSupported(device)) {
active_devices.add(device);
Reader[] Reader = new Reader[2];
Reader[i] = new Reader(mManager);
Reader[i].setOnStateChangeListener(new Reader.OnStateChangeListener() {
#Override
public void onStateChange(int slotNum, int prevState, int currState) {
Log.i("STATE CHANGE", String.valueOf(currState));
if (currState < com.acs.smartcard.Reader.CARD_UNKNOWN || currState > com.acs.smartcard.Reader.CARD_SPECIFIC) {
currState = 0;
}
if (currState == com.acs.smartcard.Reader.CARD_PRESENT) {
Log.i("CARD PRESENT", String.valueOf(slotNum));
}
}
});
i++;
}
}
this.mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
IntentFilter filter = new IntentFilter();
filter.addAction(ACTION_USB_PERMISSION);
filter.addAction("android.hardware.usb.action.USB_DEVICE_DETACHED");
registerReceiver(mReceiver, filter);
powerUp();
}
public void powerUp(UsbManager manager) {
for (UsbDevice device: active_devices) {
manager.requestPermission(device, this.mPermissionIntent);
}
}
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (MainActivity.ACTION_USB_PERMISSION.equals(action)) {
synchronized (this) {
UsbDevice device = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
if (!intent.getBooleanExtra("permission", false)) {
Log.i("Permission denied ", device.getDeviceName());
} else if (device != null) {
Log.i("Opening reader:", device.getDeviceName());
new OpenTask().execute(device);
}
}
} else if ("android.hardware.usb.action.USB_DEVICE_DETACHED".equals(action)) {
synchronized (this) {
UsbDevice device = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
if (device != null && device.equals(mReader.getDevice())) {
Log.i("Closing...", "Closing...");
new CloseTask().execute();
}
}
}
}
};
private class CloseTask extends AsyncTask<Void, Void, Void> {
private CloseTask() {
}
protected Void doInBackground(Void... params) {
mReader.close();
return null;
}
protected void onPostExecute(Void result) {
}
}
private class OpenTask extends AsyncTask<UsbDevice, Void, Exception> {
private OpenTask() {
}
protected Exception doInBackground(UsbDevice... params) {
try {
mReader.open(params[0]);
return null;
} catch (Exception e) {
return e;
}
}
protected void onPostExecute(Exception result) {
if (result != null) {
Log.i("Post Execute Result: ", result.toString());
} else {
try{
Log.i("Reader name: ", mReader.getReaderName());
} catch (Exception e){
Log.w("Error", e.getMessage());
}
int numSlots = mReader.getNumSlots();
Log.i("Number of slots: ", String.valueOf(numSlots));
}
}
}
}

Download pictures using a service

I'm trying to download pictures in the background of an app using Service (not IntentSevice)
Somehow, my code doesn't work.
I set permissions for Internet and Storage in the Manifest.
I'm thankful for any comments or answers (:
Here's my code:
For the Service and then for the MainActivity
i have already tried different links or httpURLConnection instead of the normal URL connection but that doesnt't work either.
when I run the app, it always shows my "error" toast. it doesn't even get to the Input Stream.
public class Download extends Service {
public static final String URL = "url";
public static final String FILENAME = "name";
public static final String FILEPATH = "path";
public static final String RESULT = "result";
public static final String NOTIFICATION = "notification";
public ImageView imageView1 ;
#Override
public IBinder onBind(Intent arg0){
// TODO Auto-generated method stub
return null;
}
public void onCreate(){
super.onCreate();
Toast.makeText(this,"Service is created",Toast.LENGTH_LONG).show();
}
#Override
public int onStartCommand(Intent intent, int flags, int startId){
String urlPath = intent.getStringExtra(FILEPATH);
String fileName = intent.getStringExtra(FILENAME);
int result = Activity.RESULT_CANCELED;
try {
Toast.makeText(this, "Service started", Toast.LENGTH_LONG).show();
final URL fileUrl = new URL(urlPath);
HttpURLConnection urlConnection = (HttpURLConnection) fileUrl.openConnection();
final InputStream inputStream = new BufferedInputStream(urlConnection.getInputStream());
Toast.makeText(this, "connected", Toast.LENGTH_LONG).show();
//Toast.makeText(this, "connected", Toast.LENGTH_LONG).show();
File downloadordner = new File(Environment.getExternalStorageDirectory() + "/Pictures");
if (!downloadordner.exists()) {
downloadordner.mkdirs();
}
File downloadedfile = new File(downloadordner, "Bild1" + System.currentTimeMillis() + ".png");
OutputStream outputStream = new FileOutputStream(downloadedfile);
try {
byte[] buffer = new byte[1024];
int read;
while ((read = inputStream.read(buffer)) != -1) {
outputStream.write(buffer, 0, read);
}
result = Activity.RESULT_OK;
}finally{
outputStream.flush();
outputStream.close();
inputStream.close();
}
} catch (Exception e){
e.printStackTrace();
Toast.makeText(this,"Fehler",Toast.LENGTH_LONG).show();
}
publishResults(result);
return START_STICKY;
}
private void publishResults(int result){
Intent intent = new Intent(NOTIFICATION);
intent.putExtra(RESULT,result);
sendBroadcast(intent);
}
#Override
public void onDestroy(){
super.onDestroy();
Toast.makeText(this,"Service Stopped", Toast.LENGTH_LONG).show();
System.exit(0);
}
}
public class MainActivity extends AppCompatActivity {
Button btn1;
Button btn2;
ProgressBar progbar1;
public ImageView imageView1;
private TextView downloadStatus; //neu
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
downloadStatus = (TextView) findViewById(R.id.download_status);
progbar1 = (ProgressBar) findViewById(R.id.progbar1);
btn1 = (Button) findViewById(R.id.go);
btn2 = (Button) findViewById(R.id.kill);
imageView1 = (ImageView) findViewById(R.id.bild1);
btn1.setOnClickListener(onDownloadListener());
btn2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
stopService(new Intent(getBaseContext(), Download.class));
System.exit(0);
}
});
}
private View.OnClickListener onDownloadListener(){
return new View.OnClickListener() {
#SuppressLint("SetTextI18n")
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Download.class);
intent.putExtra(Download.FILENAME,"logo.png");
intent.putExtra(Download.FILEPATH,"https://de.wikipedia.org/wiki/Kleiner_Eisvogel#/media/File:Limenitis_camilla3.jpg");
startService(intent);
downloadStatus.setText("Downloading....");
Toast.makeText(MainActivity.this, "downloading", Toast.LENGTH_LONG).show();
}
};
}
private BroadcastReceiver receiver = new BroadcastReceiver() {
#SuppressLint("SetTextI18n")
#Override
public void onReceive(Context context, Intent intent) {
Bundle bundle = intent.getExtras();
if(bundle != null){
int resultCode = bundle.getInt(Download.RESULT);
if (resultCode == RESULT_OK){
Toast.makeText(MainActivity.this,"File downloaded",Toast.LENGTH_LONG).show();
downloadStatus.setText("Download completed");
}else{
Toast.makeText(MainActivity.this,"Error",Toast.LENGTH_LONG).show();
downloadStatus.setText("Download failed");
}
}
}
};
}

Service runs on the main thread so there is a network exception NO networking is allowed on the main thread.

Custom Listener

I am working on a chat application. Currently i did like that when i open the ChatActvity, all sockets are registered and the chatting works... Now i want to change the coding structure.. I want to open the sockets in a class, not in Activity class and i need to add a listener to that class. How i implement this..?
private class Chatroom {
private static void initialise() {
// Initialising the sockets and registering listeners to each socket
}
}
I want to notify in my activity class when the socket listeners in the Chatroom class get called..

here is probably what you need :
public class RequestSender extends AsyncTask<String, Void, String> {
private final static String serverIP = "192.168.1.1";
private final static Integer serverPort = 1234;
private ServerResponseListener listener = null;
public void setServerResponseListener(ServerResponseListener listener){
this.listener=listener;
}
public interface ServerResponseListener {
public void onResponseReceive(String response);
}
#Override
protected String doInBackground(String... params) {
Socket socket = null;
try {
socket = new Socket(serverIP, serverPort);
} catch (IOException e) {
// return "server is unreachable" message or something
}
PrintWriter requestWriter = new PrintWriter(socket.getOutputStream());
BufferedReader resultReader = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
String request = params[0] //for example
requestWriter.println(request);
requestWriter.flush();
String result = null;
while ((result = resultReader.readLine()) != null) {}
return result;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
listener.onResponseReceive(result);
}
}
here is example how to execute AsynchTask from Activity :
public class MainActivity extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RequestSender requestSender = new RequestSender();
requestSender.setServerResponseListener(new RequestSender.ServerResponseListener(){
#override
public void onResponseReceive(String response){
//
}
});
requestSender.execute("message");
}
}
read this : http://developer.android.com/reference/android/os/AsyncTask.html

In Android: How can i send the result of from OnPostExecute() to other activity?

I got the result of OnPostExecute() to main activity but I want to use this result in second activity. I read and applied something with using Bundle but it doesn't run. I got error NullPointerException cause of not receiving the value in the second activity. Here is my MainActivity (It has an interface AsyncResponse ):
public class MainActivity extends Activity implements AsyncResponse
{
public String t;
public Bundle bnd;
public Intent intent;
public String sending;
private static final String TAG = "MyActivity";
ProductConnect asyncTask =new ProductConnect();
public void processFinish(String output){
sending=output;
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
asyncTask.delegate = this;
setContentView(R.layout.activity_main);
Button b = (Button) findViewById(R.id.button1);
bnd=new Bundle();
intent=new Intent(MainActivity.this, second.class);
b.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
asyncTask.execute(true);
bnd.putString("veri", sending);
intent.putExtras(bnd);
startActivity(intent);
}
});
}
// START DATABASE CONNECTION
class ProductConnect extends AsyncTask<Boolean, String, String> {
public AsyncResponse delegate=null;
private Activity activity;
public void MyAsyncTask(Activity activity) {
this.activity = activity;
}
#Override
protected String doInBackground(Boolean... params) {
String result = null;
StringBuilder sb = new StringBuilder();
try {
// http post
HttpClient httpclient = new DefaultHttpClient();
HttpGet httppost = new HttpGet(
"http://192.168.2.245/getProducts.php");
HttpResponse response = httpclient.execute(httppost);
if (response.getStatusLine().getStatusCode() != 200) {
Log.d("MyApp", "Server encountered an error");
}
BufferedReader reader = new BufferedReader(
new InputStreamReader(
response.getEntity().getContent(), "UTF8"));
sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
result = sb.toString();
Log.d("test", result);
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
return result;
}
#Override
protected void onPostExecute(String result) {
try {
JSONArray jArray = new JSONArray(result);
JSONObject json_data;
for (int i = 0; i < jArray.length(); i++) {
json_data = jArray.getJSONObject(i);
t = json_data.getString("name");
delegate.processFinish(t);
}
} catch (JSONException e1) {
e1.printStackTrace();
} catch (ParseException e1) {
e1.printStackTrace();
}
super.onPostExecute(result);
}
protected void onPreExecute() {
super.onPreExecute();
ProgressDialog pd = new ProgressDialog(MainActivity.this);
pd.setTitle("Please wait");
pd.setMessage("Authenticating..");
pd.show();
}
}
Here is My Second Activity:
public class second extends ActionBarActivity {
public CharSequence mTitle;
private static final String TAG = "MyActivity";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.second);
Bundle receive=getIntent().getExtras();
String get=receive.getString("veri");
Log.v(TAG, get);
}
What should i do?

AsyncTask.execute() is a non-blocking call. You can't set the result to the Bundle and start an Intent immediatly after execute(). That's why you are getting a NPE in your second Activity because sending isn't initialized, so it's null.
Move the code to start a new Activity with the desired data in your callback:
public void processFinish(String output){
bnd.putString("veri", output);
intent.putExtras(bnd);
startActivity(intent);
}
And make sure you call delegate.processFinished(String) if your data processing is finished. So move it out of the for loop. BTW t will only get the last "name"-String in the JSONArray. If you wanna get them all make t a String array and fill it.

As your variable t is globally declared in your activity so can directly use the value of t which you are assigning in your onPostExecute() method. Just you need to check for its null value only in your button click event as below :
b.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
asyncTask.execute(true);
if(t != null || t != "")
{
bnd.putString("veri", t);
intent.putExtras(bnd);
startActivity(intent);
}
}
});

// try this
public class MainActivity extends Activity
{
public String t;
public Bundle bnd;
public Intent intent;
private static final String TAG = "MyActivity";
ProductConnect asyncTask;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button b = (Button) findViewById(R.id.button1);
bnd=new Bundle();
intent=new Intent(MainActivity.this, second.class);
asyncTask = new ProductConnect(new ResultListener() {
#Override
public void onResultGet(String value) {
bnd.putString("veri", value);
intent.putExtras(bnd);
startActivity(intent);
}
});
b.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View arg0) {
asyncTask.execute(true);
}
});
}
class ProductConnect extends AsyncTask<Boolean, String, String> {
private ResultListener target;
public ProductConnect(ResultListener target) {
this.target = target;
}
#Override
protected String doInBackground(Boolean... params) {
String result = null;
StringBuilder sb = new StringBuilder();
try {
// http post
HttpClient httpclient = new DefaultHttpClient();
HttpGet httppost = new HttpGet(
"http://192.168.2.245/getProducts.php");
HttpResponse response = httpclient.execute(httppost);
if (response.getStatusLine().getStatusCode() != 200) {
Log.d("MyApp", "Server encountered an error");
}
BufferedReader reader = new BufferedReader(
new InputStreamReader(
response.getEntity().getContent(), "UTF8"));
sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
result = sb.toString();
Log.d("test", result);
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
return result;
}
#Override
protected void onPostExecute(String result) {
try {
JSONArray jArray = new JSONArray(result);
JSONObject json_data;
for (int i = 0; i < jArray.length(); i++) {
json_data = jArray.getJSONObject(i);
t = json_data.getString("name");
target.onResultGet(t);
}
} catch (JSONException e1) {
e1.printStackTrace();
} catch (ParseException e1) {
e1.printStackTrace();
}
super.onPostExecute(result);
}
protected void onPreExecute() {
super.onPreExecute();
ProgressDialog pd = new ProgressDialog(MainActivity.this);
pd.setTitle("Please wait");
pd.setMessage("Authenticating..");
pd.show();
}
}
interface ResultListener {
public void onResultGet(String value);
}
}

Shortly before someone posted a solution and it works without any errors but it was deleted. This solution is by this way:
public void onClick(View arg0) {
asyncTask.execute(true);
}
});
}
Then OnPostExecute changed like this:
protected void onPostExecute(String result) {
Intent passValue=new Intent(MainActivity.this, second.class);
try {
JSONArray jArray = new JSONArray(result);
JSONObject json_data;
for (int i = 0; i < jArray.length(); i++) {
json_data = jArray.getJSONObject(i);
t = json_data.getString("name");
delegate.processFinish(t);
}
passValue.putExtra("veri", t);
startActivity(passValue);
} catch (JSONException e1) {
e1.printStackTrace();
} catch (ParseException e1) {
e1.printStackTrace();
}
super.onPostExecute(result);
}
Lastly in my second activity receive the string by this way:
String receivedVal= getIntent().getExtras().getString("veri");
Log.v(TAG, receivedVal);
Thank you someone who posted this solution shortly before :)