Develop Reference

Crash in Android UDP server

UPDATED:
I get crash in this Android UDP server example:
//------------------------------------------------------------
public class AsyncReceiveUdp2 extends AsyncTask<String, Void, Boolean> {
#Override
protected Boolean doInBackground(String... f_url) {
int udp=111;
String txt="";
byte[] packet = new byte[2000];
DatagramPacket dp = new DatagramPacket(packet, packet.length);
DatagramSocket ds = null;
try {
ds = new DatagramSocket(udp);
ds.setSoTimeout(10000);
printLog("Ready");
ds.receive(dp);
printLog("Received");
...
} catch (SocketException e) {
printLog("Error1");
e.printStackTrace();
} catch (IOException e) {
printLog("Error2");
e.printStackTrace();
} finally {
if (ds != null) {
ds.close();
}
}
return null;
}
}
I get my "error2" message.
The reason is "java.net.SocketTimeoutException".
It happens after 10 seconds.
But I sent UDP packet from another computer.
Hmm, I don't understand how it works....
Any ideas please!
Sorry for extra line, the site said that my post is mostly code
Sorry for extra line, the site said that my post is mostly code
Sorry for extra line, the site said that my post is mostly code

You cannot run network threads on the UI thread, Android policy forbids it. Make a new thread or use AsyncTask

android asynctask crash when trying to load an heavy page

I'm programming an app with my brother, and today unfortunately, I encountered with a problem.
When the app load a php page via my asynctask class it works fine. but I would like to program this situation: if the remote server is down, or crash, and doesnt display the right page, the application will show error message. but instead, the app crashes =[
I tried to load this page, for example:
http://alonadoni.com/sql3.php
(I want to simulate that there is a problem with the server. the regular page is sql2.php and it works fine when the server works)
When the app try to load this page (sql3.php) , the app crashes.
I did another experiment : I created a file sql3.php, and wrote "aaaaaaaa" in the page, the app doesn't crash in this situation. it downloaded the data "aaaaa". in this case, the app show jsonexecption error.
Unfortunately, I can't get logcat because my old computer can't run emulators, and my phone also can't connect to my computer on developer mode =[ When I try application I create an apk then transfer the file to my phone and install.
my code is:
in OnCreate:
String serverURL = sss() + "sql3.php?imei=" + imei;
new LongOperation().execute(serverURL);
outside OnCreate:
private class LongOperation extends AsyncTask<String, Void, Void> {
private final HttpClient Client = new DefaultHttpClient();
private String Error = null;
protected void onPreExecute() {
}
protected Void doInBackground(String... urls) {
try {
HttpGet httpget = new HttpGet(urls[0]);
ResponseHandler<String> responseHandler = new BasicResponseHandler();
data[x] = Client.execute(httpget, responseHandler);
} catch (ClientProtocolException e) {
Error = e.getMessage();
Toast.makeText(getApplicationContext(),"error2" , Toast.LENGTH_LONG).show();
cancel(true);
} catch (IOException e) {
Error = e.getMessage();
Toast.makeText(getApplicationContext(),"error34" , Toast.LENGTH_LONG).show();
cancel(true);
}
return null;
}
public void onPostExecute(Void unused) {
if (Error != null) {
} else {
try {
JSONObject json = new JSONObject(data[x]);
name = json.getString("name");
} catch (JSONException e) {
Toast.makeText(getApplicationContext(),"e" + e, Toast.LENGTH_LONG).show();
}
}
x++;
}
}

DoInBackground of asynctask needs to contain only NON UI work , hence referring to context and performing UI operations in UI thread may cause crash.
You can perform UI operations in postexecute of asynctask.
Hence Removing toast from above code which refers to UI operation will solve your issue

AsyncTask hangs on at beginning

AsyncTask works fine in Android 4.x, but not for Android 2.3.6. I've step-by-step debugged Android 2.3.6 with a physical mobile device.
It hangs on here:
myTask = new GetDataFromServer();
GetDataFromServer is the class of AsyncTask.
What's going on?
Here under is my code, I only used 1 AsyncTask in my code and received messages from server.
that's all.
class GetDataFromServer extends AsyncTask<String, String, String>
{
protected void onPreExecute ()
{
progressDialog1=ProgressDialog.show(MainActivity.this, "Loading data", "Please wait...",true);
}
protected String doInBackground(String... params)
{
String resulttxt="";
try {
serverIp = InetAddress.getByName("192.168.1.123");
int serverPort=31000;
Socket clientSocket=new Socket(serverIp,serverPort);
BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
bw.write(params[0]);
bw.flush();
BufferedReader br=new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
resulttxt=br.readLine();
if(resulttxt.contains("OK"))
{
publishProgress(resulttxt);
}
else
{
publishProgress(resulttxt);
clientSocket.close();
bw.close();
br.close();
return null;
}
resulttxt="";
resulttxt=br.readLine();
resulttxt=resulttxt.trim();
clientSocket.close();
} catch (IOException e) {
if(Status_txt!=null)
Status_txt.append( "Server is done.");
}
catch (NetworkOnMainThreadException e){
if(Status_txt!=null)
Status_txt.append( "NetworkOnMainThreadException");
}
return resulttxt;
}
protected void onProgressUpdate(String...inStr){
String[] strData=inStr[0].split("_");
String szTemp="Last Purchase Date: ";
szTemp+=strData[1];
szTemp+=" ,Valid days: ";
szTemp+=strData[2];
//Status_txt.setText(szTemp);
if(Status_txt!=null)
Status_txt.setText("You Are The Super User");
}
protected void onPostExecute(String data) {
tl_prediction2.removeAllViews();
if (data == null)
{
}
else {
if((data.contains("#")==true) || (data.contains("*")==true)
||data.contains("&")==true)
{
String[] arrayTmp=data.split("#");
for(Integer i=0;i<arrayTmp.length;i++)
{
String[] SubArrayTmp=arrayTmp[i].split("_");
tl_prediction2.addView(generateRow(4,SubArrayTmp));
}
}
}
progressDialog1.dismiss();
}
};

Since you haven't posted any code, I could only give you some random probable solutions:
May be your AsyncTask is taking a lot of time to download. Trying increasing its priority using android.os.Process.setThreadPriority(9) inside doInBackground()
Check if you have other previous running long AsyncTask in your code. AsyncTask by default operates on a single background thread. That means your AsyncTask task wouldn't be executed unless your previous AsyncTask are done. To allow parallel execution use executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, params). You can read more here
Check for Internet and other permissions in Manifest. This is mostly where people make mistake.

AsyncTask works with ThreadPool. If there too many synctasks are executing, the later AsyncTask will be blocked by others. I think you can use the thread tool in DDMS to check the How many ayncTasks are executing.

Http Response inside a service in Android

Hi I have a service in Android that handles the HTTP method POST as specified below. Now, I need to call an Intent in
replaceResourceSegment()
method. It has a handler that takes nearly 90 seconds to complete the task. Within that time, control exits the handler block. But I want my program to continue within handler for POST. In short, I want my service to pause for sometime inside the POST handler, till my Intent (with handler) completes its execution and I need to delay sending the response of HTTP Post. Can some one guide me how to do this implementation?
if(method.equals("POST"))
{
conn.receiveRequestEntity((HttpEntityEnclosingRequest)request);
HttpEntity entity = ((HttpEntityEnclosingRequest)request).getEntity();
String content_type = ""+entity.getContentType();
JSONReceived = EntityUtils.toString(entity);
if(content_type.contains("json"))
{
Log.d(TAG,"Content received is: "+JSONReceived);
bufferedWriter = new BufferedWriter(new FileWriter(new File(getFilesDir()+File.separator+constants.UPDATED_SCRIPT_FILE)));
bufferedWriter.write(JSONReceived);
bufferedWriter.close();
try {
parseJSON(JSONReceived);
replaceResourceSegment(); //Call to an intent with startActivityForResult()
continueExecution(); //Continue the execution from here
} catch (IOException e) {
e.printStackTrace();
Log.d(TAG,"IOException line 157");
}
Code for sending response back:
HttpResponse postResponse = new BasicHttpResponse(HttpVersion.HTTP_1_1, 200, "OK");
postResponse.setEntity(new StringEntity("Got it"));
conn.sendResponseHeader(postResponse);
conn.sendResponseEntity(postResponse);

I managed to solve the problem by using a boolean variable with default value false. It will be checked periodically and keeps the control inside the POST method's handler.
android.os.SystemClock.sleep(30000); //Sleeps for 30 seconds and invoke busy waiting in a thread
Thread syncThread = new Thread(new LoopCheck());
syncThread.start();
synchronized(syncThread)
{
Log.d(TAG,"Inside synchronized blockk");
try
{
syncThread.wait();
}catch(InterruptedException ie){
ie.printStackTrace();
}
}
The thread class is defined as below:
class LoopCheck extends Thread{
public LoopCheck(){
}
public void run(){
while(true)
{
try {
Thread.sleep(10000);
if(write)
{
write = false;
synchronized(syncThread)
{
syncThread.notify();
}
break;
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

Android NullPointerException being thrown in Synchronized Method

I have an android app written in java.
The app basically connects to a device which sends the app messages. The app waits for the messages to come in and then reports them, before processing each message.
I have a Connection class and a Listener class.
The Connection class is started via the constructor, which sets up the Listener class to listen for messages coming in from the device.
When a message comes in, the Listener sends the message to a method in the Connection class, reportMessage(). This is where the message is processed.
The Listener class is on a separate thread.
The code is shown below.
public class Connection
{
private String response;
private String newResponse;
private DataInputStream reader;
private DataOutputStream writer;
private Socket socket;
private boolean keepListening;
private Listener listener;
public Connection (String _ipAddress, int portNumber)
{
try
{
socket = new Socket(_ipAddress, _port); //Connect to the server and its socket
writer = new DataOutputStream(socket.getOutputStream()); //Connect to the server to receive and send messages
reader = new DataInputStream(socket.getInputStream());
listener = new Listener(reader, this); //Create a new listener for the client
new Thread(listener).start(); //Set the listener off running
}
catch (Exception e)
{
...
}
}
public synchronized void reportMessage(String message)
{
try
{
if("".equals(newResponse))
{
newResponse = new String();
}
newResponse = newResponse + message;
System.out.println("Message Received: " + newResponse);
processMessage(); //Process the message
}
catch (Exception e)
{
response = e.getCause().toString();
}
}
}
public class Listener implements Runnable
{
private DataInputStream reader = null;
private boolean keepListening;
private String serverMessage;
private Connection connection;
public Listener (DataInputStream inFromServer, Connection connection)
{
reader = inFromServer;
//Get the client connection's message transfer
keepListening = true;
this.connection = connection;
}
public void run()
{
while (keepListening)
{
try
{
if (reader.available() > 0)
{
byte[] readInData = new byte[reader.available()]; //Initialise the array
reader.read (readInData); //Read in the data
serverMessage = Utils.byteToString(readInData);
connection.reportMessage(serverMessage); //Report the message
}
}
catch (IOException e)
{
System.out.println("Error reading." + e.getLocalizedMessage().toString());
keepListening = false;
}
keepListening = connection.getKeepListening();
}
}
}
This works well for a time, then sometimes I receive an error which crashes the program.
When running in debug mode, I get a NullPointerException thrown on whatever is the first line of reportMessage() in the Connection class.
The program is suspended on whatever line is the first line, whether it is a System.out.println or a line of actual code.
And the error doesn't get caught by the try and catch. It crashes the program and there is no handling of the error even though it occurs in the try and catch.
This leads me to believe the error is not being thrown by anything in the reportMessage() method. If this is the case, then perhaps the error is being thrown in the Listener class .run().
However, I cannot see where any NullPointerException can be thrown from, as I have tried to make all the checks and when it is thrown, it is thrown when there are messages being sent.
The debugger says "An exception stack trace is not available".
The LogCat says:
08-21 10:35:57.894: E/AndroidRuntime(1118): FATAL EXCEPTION: Thread-12
08-21 10:35:57.894: E/AndroidRuntime(1118): java.lang.NullPointerException
08-21 10:35:57.894: E/AndroidRuntime(1118):atCom.que.wifiaudio.Connection.reportMessage(Connection.java:339)
08-21 10:35:57.894: E/AndroidRuntime(1118): at com.que.wifiaudio.Listener.reportIncomingMessage(Listener.java:93)
08-21 10:35:57.894: E/AndroidRuntime(1118): at com.que.wifiaudio.Listener.run(Listener.java:67)
08-21 10:35:57.894: E/AndroidRuntime(1118): at java.lang.Thread.run(Thread.java:1102)
Can anyone help me?
I need to know what is throwing the NullPointerException and how to stop it!

Turns out it was the
catch (Exception e)
{
response = e.getCause().toString();
}
The processData() method was throwing an exception which was being caught, but the Exception's cause was Null, which was throwing the error.