This question already has answers here:
How can I fix 'android.os.NetworkOnMainThreadException'?
(66 answers)
Closed 9 years ago.
I am new to android. My project is related to networking. I am getting this error
FATAL EXCEPTION: main
android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java1133)
...
...
My code is :
package com.example.simpleclientactivity;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class SimpleClientActivity extends Activity {
private Socket client;
private PrintWriter printwriter;
private EditText textField1;
private Button button;
private String messsage;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
textField1 = (EditText) findViewById(R.id.editText1); //reference to the text field
button = (Button) findViewById(R.id.button1); //reference to the send button
//Button press event listener
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Context context = getApplicationContext();
CharSequence text = "Hello toast!";
int duration = Toast.LENGTH_SHORT;
Toast toast = Toast.makeText(context, text, duration);
toast.show();
messsage = textField1.getText().toString(); //get the text message on the text field
textField1.setText(""); //Reset the text field to blank
try {
client = new Socket("10.0.2.2", 4444); //connect to server
printwriter = new PrintWriter(client.getOutputStream(),true);
printwriter.write(messsage); //write the message to output stream
printwriter.flush();
printwriter.close();
client.close(); //closing the connection
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
}
Here is main.xml code
<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: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" >
<EditText
android:id="#+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"`enter code here`
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="83dp"
android:ems="10"
android:text="Client" >
<requestFocus />
</EditText>
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/editText1"
android:layout_centerHorizontal="true"
android:layout_marginTop="53dp"
android:text="Send" />
</RelativeLayout>
It's not even displaying the toast message after clicking the button. However it's showing error in android.os.NetworkOnMainThreadException.
Try this..
This exception is thrown when an application attempts to perform a networking operation on its main thread
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Context context = getApplicationContext();
CharSequence text = "Hello toast!";
int duration = Toast.LENGTH_SHORT;
Toast toast = Toast.makeText(context, text, duration);
toast.show();
messsage = textField1.getText().toString(); //get the text message on the text field
textField1.setText(""); //Reset the text field to blank
new MyClass().execute(messsage);
}
});
MyClass.class AsyncTask
class MyClass extends AsyncTask<String, Void, String> {
private Exception exception;
protected String doInBackground(String... messsage) {
try {
client = new Socket("10.0.2.2", 4444); //connect to server
printwriter = new PrintWriter(client.getOutputStream(),true);
printwriter.write(messsage); //write the message to output stream
printwriter.flush();
printwriter.close();
client.close(); //closing the connection
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
protected void onPostExecute(String result) {
// TODO: check this.exception
// TODO: do something with the feed
}
}
You cannot perform network IO on the UI thread on Honeycomb. Technically it is possible on earlier versions of Android, but is a really bad idea as it will cause your app to stop responding, and can result in the OS killing your app for being badly behaved. You'll need to run a background process or use AsyncTask to perform your network transaction on a background thread.
There is an article about Painless Threading on the Android developer site which is a good introduction to this, and will provide you with much better depth of answer than can be realistically provided here.
You have to put your code that access the internet on a thread
new Thread(new Runnable(){
#Override
public void run(){
//your code that access internet here
}
}).start();
try this code
package com.example.simpleclientactivity;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class SimpleClientActivity extends Activity {
private Socket client;
private PrintWriter printwriter;
private EditText textField1;
private Button button;
private String messsage;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
textField1 = (EditText) findViewById(R.id.editText1); //reference to the text field
button = (Button) findViewById(R.id.button1); //reference to the send button
//Button press event listener
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Context context = getApplicationContext();
CharSequence text = "Hello toast!";
int duration = Toast.LENGTH_SHORT;
Toast toast = Toast.makeText(context, text, duration);
toast.show();
messsage = textField1.getText().toString(); //get the text message on the text field
textField1.setText(""); //Reset the text field to blank
new GetCategory().execute(message);
}
});
}
//add inner class
class GetCategory extends AsyncTask<Void, Void, ArrayList<AbstractDetail>>{
protected ArrayList<AbstractDetail> doInBackground(String... messsage) {
try {
client = new Socket("10.0.2.2", 4444); //connect to server
printwriter = new PrintWriter(client.getOutputStream(),true);
printwriter.write(messsage); //write the message to output stream
printwriter.flush();
printwriter.close();
client.close(); //closing the connection
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(ArrayList<AbstractDetail> result)
{
}
}
}
}
Problem
You can not access network over UI thread. You are accessing Network through UI thread that's why you are getting NetworkOnMainThreadException.
Solution
Create new thread and access Network over that Thread.
OR
Use AsyncTask to do network related work on doInBackgroung() and for updating UI onPostExecute().
Related
I have java code that sends strings via ip to a python script. The code works perfectly with the emulator but when I successfully install the app via usb to my phone it does not work. Here is the code:
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
public class MainActivity extends AppCompatActivity {
public String message;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Button btn_python = findViewById(R.id.python);
final Button btn_movie = findViewById(R.id.movie);
final Button btn_hw = findViewById(R.id.homework);
btn_python.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view1) {
send py = new send();
message = "python";
Log.i("Button", "Button works");
System.out.println("whatever");
py.execute();
}
});
btn_movie.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view2) {
send mov = new send();
message = "movie";
mov.execute();
}
});
btn_hw.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view2) {
send hw = new send();
message = "homework";
hw.execute();
}
});
}
class send extends AsyncTask<Void,Void,Void>{
Socket s;
PrintWriter pw;
#Override
protected Void doInBackground(Void...params) {
System.out.println("whatevernumbertwo");
try {
System.out.println("whatevernumberthree");
s = new Socket("ip address", 7800);
Log.i("Socket", "connects to socket");
pw = new PrintWriter(s.getOutputStream());
Log.i("output stream", "Output stream works");
pw.write(message);
Log.i("write", "Write works");
pw.flush();
Log.i("flush", "Flush works");
pw.close();
s.close();
} catch (UnknownHostException e) {
System.out.println("Fail");
e.printStackTrace();
} catch (IOException e) {
System.out.println("Fail");
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}
}
As I mentioned this works on the emulator but not on the actual device. The proper permissions have also been given. What am I doing wrong? Thanks in advance.
After much digging around, it turned out to be the server's firewall all along. That explains why (apparently) no exception was thrown, and why the code didn't seem to execute; it was executing, it was just getting stuck inside Socket() (during the connect).
Surely Socket() is, in fact, throwing an IOException; it probably just takes a while.
The code works on the emulator because, as it is operating on the same machine, it is behind the firewall.
I want to display a progressdialog when a client sends request to the server..the request should be done in background...but i am getting a force close when i use the AsyncTask..Please help ..Thank you
package com.example.client;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
public static ProgressDialog Dialog;
String s1;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.button1).setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// sendreq();
new SendUserTask().execute();
}
});
}
public String sendreq() {
try {
// TODO Auto-generated method stub
SocketAddress sockaddr = new InetSocketAddress("192.168.7.116",
9011);
Socket serversocket = new Socket();
serversocket.connect(sockaddr, 10000);
serversocket.setSoTimeout(10000);
DataOutputStream out = new DataOutputStream(
serversocket.getOutputStream());
out.flush();
DataInputStream in = new DataInputStream(
serversocket.getInputStream());
out.flush();
String msg = "";
msg = "hi";
out.writeBytes(msg);
out.flush();
byte[] message = new byte[100];
in.read(message);
s1 = new String(message);
Toast.makeText(getApplicationContext(), s1, Toast.LENGTH_LONG)
.show();
((TextView) findViewById(R.id.textView1)).setText(s1);
in.close();
out.close();
serversocket.close();
} catch (Exception e) {
Toast.makeText(getApplicationContext(), String.valueOf(e),
Toast.LENGTH_LONG).show();
}
return null;
}
private class SendUserTask extends AsyncTask<Void, Void, String> {
#Override
protected void onPreExecute() {
// TODO Auto-generated method stub
Dialog = ProgressDialog.show(MainActivity.this, "",
"Logging In....", true);
super.onPreExecute();
}
protected void onPostExecute(String s) {
if (Dialog.isShowing())
Dialog.dismiss();
}
#Override
protected String doInBackground(Void... params) {
// TODO Auto-generated method stub
try {
return sendreq();
} catch (Exception e) {
Toast.makeText(getApplicationContext(), String.valueOf(e),
Toast.LENGTH_SHORT).show();
}
return null;
}
}
}
this ((TextView) findViewById(R.id.textView1)).setText(s1); is executed from the background thread. you cannot access UI elements outside the UI thread.
You need to move that part to either onProgressUpdate or onPostExecute, or to run it in a runOnUiThread Runnable.
doInBackgorund() is a non-UI thread and you cannot access UI elements inside it. The code inside doInBackground() runs on a separate non-ui thread which does not have access to the UI elements defined in your layout. Also, since you are calling another Activity via intents, you should always keep in mind that an Activity runs on the UI thread and hence you should never start another Activity from inside a non-ui thread.
So, remove the code " ((TextView) findViewById(R.id.textView1)).setText(s1); " accessing the UI elements from inside of doInBackground() and instead put it inside onPostExecute(), which is a UI thread and is called after doInBackground() finishes the background processing.
Ok.... After googling a lot i finally came to understand that you cant access UI elements from main thread into a new non-UI thread....So you cant use elements like textview or even getApplicationContext mtd tht v use for toast in the dobackground mtd or even in anyother mts that the dobackground is calling....This also applies for the new Thread() using runnable..Thank you njzk2 for your help :)
i got a class i made, that makes a simple GET request and displays toast messege with the response...
if i call the function from a bottom event click it displays the messege with the data returned, just ok.
but if i call the same function from a brodcast reciver class, it just showing the massege with the data '' (null)
i belive that it showing the massege before i could get the data, and with the button it waits for the data..
how can i make it work from the brodcast reciver?
the class:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import android.app.Activity;
import android.content.Context;
import android.widget.Toast;
public class myclass{
public static void doHttpRequest(String param1, Context context){
String ret="";
try {
URL url = new URL("http://website.com/page?param="+param1);
HttpURLConnection con = (HttpURLConnection) url
.openConnection();
ret=readStream(con.getInputStream());
} catch (Exception e) {
e.printStackTrace();
}
CharSequence text = "return data- "+ret;
int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(context, text, duration);
toast.show();
}
private static String readStream(InputStream in) {
BufferedReader reader = null;
String line = "";
String alllines = "";
try {
reader = new BufferedReader(new InputStreamReader(in));
while ((line = reader.readLine()) != null) {
alllines=alllines+line;
}
return alllines;
} catch (IOException e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return alllines;
}
}
from the button it works fine:
final Button button = (Button) findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
myclass.doHttpRequest("blabla", getBaseContext());
}});
from the brodcast reciver witch in different class it won't return data, but shows the toast..
public class CustomBroadcastReceiver extends BroadcastReceiver {
private static final String TAG = "CustomBroadcastReceiver";
#Override
public void onReceive(Context context, Intent intent) {
myclass.doHttpRequest("blabla", context);
break;
} }
}
please HELP.... :) THANKS
All fixed.. it's seems to be a project settings error, or premmisions error (but i had the premissions in the manifest... must not apply in the apk while compiling)
i copied the classes to enother project made by erlier version of eclipse, and it's works there like a charm...
thanks anyway..
i tried for hours to fix it in the code.. and it was the settings....
I created a myclass.java and CustomBroadcastReceiver.java and tried your code by removing the break statement and one extra curly brace from the CustomBroadcastReceiver.java class and it worked fine for me.
The following code in Activity class demonstrates registering, uninteresting receiver and a Handler for a sample/test broadcast.
CustomBroadcastReceiver customBroadcastReceiver;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
customBroadcastReceiver = new CustomBroadcastReceiver();
registerReceiver(cusoBroadcastReceiver, new IntentFilter("com.example.app.testbroadcast"));
// For test broadcast only.
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
sendBroadcast(new Intent("com.example.app.testbroadcast"));
}
}, 2000);
}
#Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
unregisterReceiver(customBroadcastReceiver);
}
Hope this helps.
In my application i want to do bluetooth chat. I'm facing a problem in threading. In my application my android phone will work as server which has a blocking statement
socket=mServerSocket.accept();
for this purpose i've created a child thread so that it will run separately. But before finishing this child thread main thread goes down giving Force Close and if i use the .join() method it hangs up my UI.
What is the solution to run both threads parallel?
this is my code
main Activity
package com.my.bluechat_2_1;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class BlueChat extends Activity {
/** Called when the activity is first created. */
private BlueHandler btHandler=null;
private BluetoothAdapter btAdapter = null;
private Context context=this;
TextView chatWindow=null;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
chatWindow=(TextView)findViewById(R.id.textView1);
doStart();
}
private void doStart(){
Button btnStart=(Button)findViewById(R.id.button1);
btnStart.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View arg0) {
// Get local Bluetooth adapter
btAdapter = BluetoothAdapter.getDefaultAdapter();
// If the adapter is null, then Bluetooth is not supported
if(btAdapter == null)
{
Toast.makeText(context, "Device does not support Bluetooth", Toast.LENGTH_LONG).show();
}
if (!btAdapter.isEnabled()) {
Intent discoverableIntent = new
Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300);
startActivity(discoverableIntent);
}
chatWindow.append("Waiting for connection...\n");
btHandler=new BlueHandler(context,chatWindow,btAdapter);
Thread acceptThread=new Thread(btHandler);
acceptThread.start();
}
});
}
}
BlueHandler
package com.my.bluechat_2_1;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.UUID;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothServerSocket;
import android.bluetooth.BluetoothSocket;
import android.content.Context;
import android.widget.TextView;
import android.widget.Toast;
public class BlueHandler implements Runnable{
// Name for the SDP record when creating server socket
private static final String SMARTCAM_BT_SERVICE_NAME = "SmartCam";
// Unique UUID for this application
private static final UUID SMARTCAM_BT_SERVICE_UUID = UUID.fromString("95b82690-4c94-11e1-b86c-0800200c9a66");
private BluetoothAdapter btAdapter = null;
private BluetoothServerSocket btServerSocket = null;
private BluetoothSocket btSocket = null;
private InputStream btInputStream=null;
private Context contextObj=null;
private TextView textView;
public BlueHandler(Context contextObj,TextView textView,BluetoothAdapter btAdapter){
this.contextObj=contextObj;
this.btAdapter=btAdapter;
this.textView=textView;
try {
btServerSocket=this.btAdapter.listenUsingRfcommWithServiceRecord(SMARTCAM_BT_SERVICE_NAME, SMARTCAM_BT_SERVICE_UUID);
} catch (IOException e) {
// TODO Auto-generated catch block
Toast.makeText(this.contextObj, "Service not created", Toast.LENGTH_LONG);
}
}
#Override
public void run() {
// TODO Auto-generated method stub
textView.append("Inside child thread.\n");
textView.append(btServerSocket+"\n");
while (true) {
try {
btSocket = btServerSocket.accept();
} catch (IOException e) {
break;
}
// If a connection was accepted
if (btSocket != null) {
// Do work to manage the connection (in a separate thread)
try {
btServerSocket.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
break;
}
}
textView.append("Connected.\n");
try {
btInputStream=btSocket.getInputStream();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
byte[] buffer = new byte[1024]; // buffer store for the stream
String s;
int bytes; // bytes returned from read()
// Keep listening to the InputStream until an exception occurs
while (true) {
try {
// Read from the InputStream
bytes=btInputStream.read(buffer);
s= new String(buffer);
// Send the obtained bytes to the UI Activity
textView.append("received ::" +s+"\n");
} catch (IOException e) {
break;
}
}
}
}
You're probably getting a crash because you're accessing a textView on the worker thread. You'll need to use TextView.post(Runnable) to make that not happen.
In reality you should be using a bindable Service to do this kind of work. You can post back to the UI via broadcast intents or callback methods, That way you don't have to worry about rotation bugs.
Are you performing a long operation in the constructor of your children thread? Each long operation must be done in the run() method.
Most of the network socket examples I found for Android were one directional only. I needed a solution for a bi-directional data stream. I eventually learned of the AsyncTask. This example shows how to get data from a socket and send data back to it. Due to the blocking nature of a socket that is receiving data, that blocking needs to run in a thread other than the UI thread.
For the sake of example, this code connects to a webserver. Pressing the "Start AsyncTask" button will open the socket. Once the socket is open, the web server waits for a request. Pressing the "Send Message" button will send a request to the server. Any response from the server will be displayed in the TextView. In the case of http, a web server will disconnect from the client once all the data has been sent. For other TCP data streams, the connection will stay up until one side disconnects.
Screenshot:
AndroidManifest.xml:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.exampleasynctask"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" />
<uses-permission android:name="android.permission.INTERNET" />
<application android:icon="#drawable/icon" android:label="#string/app_name">
<activity android:name=".MainActivity"
android:label="#string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
res\layout\main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button android:id="#+id/btnStart" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Start AsyncTask"></Button>
<Button android:id="#+id/btnSend" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Send Message"></Button>
<TextView android:id="#+id/textStatus" android:textSize="24sp" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Status Goes Here" />
</LinearLayout>
src\com.exampleasynctask\MainActivity.java:
package com.exampleasynctask;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
Button btnStart, btnSend;
TextView textStatus;
NetworkTask networktask;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
btnStart = (Button)findViewById(R.id.btnStart);
btnSend = (Button)findViewById(R.id.btnSend);
textStatus = (TextView)findViewById(R.id.textStatus);
btnStart.setOnClickListener(btnStartListener);
btnSend.setOnClickListener(btnSendListener);
networktask = new NetworkTask(); //Create initial instance so SendDataToNetwork doesn't throw an error.
}
private OnClickListener btnStartListener = new OnClickListener() {
public void onClick(View v){
btnStart.setVisibility(View.INVISIBLE);
networktask = new NetworkTask(); //New instance of NetworkTask
networktask.execute();
}
};
private OnClickListener btnSendListener = new OnClickListener() {
public void onClick(View v){
textStatus.setText("Sending Message to AsyncTask.");
networktask.SendDataToNetwork("GET / HTTP/1.1\r\n\r\n");
}
};
public class NetworkTask extends AsyncTask<Void, byte[], Boolean> {
Socket nsocket; //Network Socket
InputStream nis; //Network Input Stream
OutputStream nos; //Network Output Stream
#Override
protected void onPreExecute() {
Log.i("AsyncTask", "onPreExecute");
}
#Override
protected Boolean doInBackground(Void... params) { //This runs on a different thread
boolean result = false;
try {
Log.i("AsyncTask", "doInBackground: Creating socket");
SocketAddress sockaddr = new InetSocketAddress("192.168.1.1", 80);
nsocket = new Socket();
nsocket.connect(sockaddr, 5000); //10 second connection timeout
if (nsocket.isConnected()) {
nis = nsocket.getInputStream();
nos = nsocket.getOutputStream();
Log.i("AsyncTask", "doInBackground: Socket created, streams assigned");
Log.i("AsyncTask", "doInBackground: Waiting for inital data...");
byte[] buffer = new byte[4096];
int read = nis.read(buffer, 0, 4096); //This is blocking
while(read != -1){
byte[] tempdata = new byte[read];
System.arraycopy(buffer, 0, tempdata, 0, read);
publishProgress(tempdata);
Log.i("AsyncTask", "doInBackground: Got some data");
read = nis.read(buffer, 0, 4096); //This is blocking
}
}
} catch (IOException e) {
e.printStackTrace();
Log.i("AsyncTask", "doInBackground: IOException");
result = true;
} catch (Exception e) {
e.printStackTrace();
Log.i("AsyncTask", "doInBackground: Exception");
result = true;
} finally {
try {
nis.close();
nos.close();
nsocket.close();
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
Log.i("AsyncTask", "doInBackground: Finished");
}
return result;
}
public void SendDataToNetwork(String cmd) { //You run this from the main thread.
try {
if (nsocket.isConnected()) {
Log.i("AsyncTask", "SendDataToNetwork: Writing received message to socket");
nos.write(cmd.getBytes());
} else {
Log.i("AsyncTask", "SendDataToNetwork: Cannot send message. Socket is closed");
}
} catch (Exception e) {
Log.i("AsyncTask", "SendDataToNetwork: Message send failed. Caught an exception");
}
}
#Override
protected void onProgressUpdate(byte[]... values) {
if (values.length > 0) {
Log.i("AsyncTask", "onProgressUpdate: " + values[0].length + " bytes received.");
textStatus.setText(new String(values[0]));
}
}
#Override
protected void onCancelled() {
Log.i("AsyncTask", "Cancelled.");
btnStart.setVisibility(View.VISIBLE);
}
#Override
protected void onPostExecute(Boolean result) {
if (result) {
Log.i("AsyncTask", "onPostExecute: Completed with an Error.");
textStatus.setText("There was a connection error.");
} else {
Log.i("AsyncTask", "onPostExecute: Completed.");
}
btnStart.setVisibility(View.VISIBLE);
}
}
#Override
protected void onDestroy() {
super.onDestroy();
networktask.cancel(true); //In case the task is currently running
}
}
The SendDataToNetwork task runs in the main ui thread, meaning it will crash a Honeycomb or higher app due to NetworkOnMainThreadException Fatal exception. Here's what my SendDataToNetwork looks like to avoid this issue:
public boolean sendDataToNetwork(final byte[] cmd) {
if (_nsocket.isConnected()) {
Log.i(TAG, "SendDataToNetwork: Writing received message to socket");
new Thread(new Runnable() {
public void run() {
try {
_nos.write(cmd);
} catch (Exception e) {
e.printStackTrace();
Log.i(TAG, "SendDataToNetwork: Message send failed. Caught an exception");
}
}
}).start();
return true;
}
Log.i(TAG, "SendDataToNetwork: Cannot send message. Socket is closed");
return false;
}
Your SendDataToNetwork does not run on the same thread as doInBackground(). There is a possibility that SendDataToNetwork would start sending data before socket is ready.
To avoid all this just use SendDataToNetwork to save data and signal to background thread that data is ready to be sent.
Since there is possibility that user can press button multiple times, while the old data is still being sent, you should have synchronized Queue inside NetworkTask. Then:
Background thread sets up the socket connection and then goes to sleep (via wait()).
On button press, SendDataToNetwork adds data to queue and wakes up the background thread (via notify()).
When background thread wakes up, it first checks the finish flag. If set, it closes connections and exits. If not it reads data from Queue, sends it to network and goes back to sleep.
You should have finish() method which sets a finish flag (atomic variable, like boolean) and wakes the background thread. This is a way to gracefully exit the background thread.
Take a look at how thread synchronization is done: http://www.jchq.net/tutorial/07_03Tut.htm
More interactive example
Similar to the OP's, but you can control host, port and message + there is a popup error notification if the connection failed.
Usage 1:
get Android and a Linux desktop on a LAN
find the IP of the desktop with ifconfig
run netcat -l 12345 on a terminal
on Android, fill in the IP of the desktop
click contact server
on the terminal, type the reply, and hit Ctrl + D
it appears on the output: section
Usage 2:
hostname google.com
port 80
Message: "GET / HTTP/1.1\r\nHost: google.com\r\n\r\n"
Note that some HTTP servers won't close after the reply expecting further requests, and the application will hang until they timeout. Such servers expect you to parse the Content-Width header and close yourself.
If the connection fails, an alert message is shown to the user on a dialog.
Code
Add to AndroidManifest.xml:
<uses-permission android:name="android.permission.INTERNET" />
And the main activity is:
import android.app.Activity;
import android.app.AlertDialog;
import android.app.IntentService;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.ScrollView;
import android.widget.TextView;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;
public class Main extends Activity {
final static String TAG = "AndroidCheatSocket";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final LinearLayout linearLayout = new LinearLayout(this);
linearLayout.setOrientation(LinearLayout.VERTICAL);
TextView textView;
final String defaultHostname = "192.168.0.";
textView = new TextView(this);
textView.setText("hostname / IP:");
linearLayout.addView(textView);
final EditText hostnameEditText = new EditText(this);
hostnameEditText.setText(defaultHostname);
hostnameEditText.setSingleLine(true);
linearLayout.addView(hostnameEditText);
textView = new TextView(this);
textView.setText("port:");
linearLayout.addView(textView);
final EditText portEditText = new EditText(this);
portEditText.setText("12345");
portEditText.setSingleLine(true);
linearLayout.addView(portEditText);
textView = new TextView(this);
textView.setText("data to send:");
linearLayout.addView(textView);
final EditText dataEditText = new EditText(this);
dataEditText.setText(String.format("GET / HTTP/1.1\r\nHost: %s\r\n\r\n", defaultHostname));
linearLayout.addView(dataEditText);
final TextView replyTextView = new TextView(this);
final ScrollView replyTextScrollView = new ScrollView(this);
replyTextScrollView.addView(replyTextView);
final Button button = new Button(this);
button.setText("contact server");
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
button.setEnabled(false);
new MyAsyncTask(Main.this, replyTextView, button).execute(
hostnameEditText.getText().toString(),
portEditText.getText().toString(),
dataEditText.getText().toString());
}
});
linearLayout.addView(button);
textView = new TextView(this);
textView.setText("output:");
linearLayout.addView(textView);
linearLayout.addView(replyTextScrollView);
this.setContentView(linearLayout);
}
private class MyAsyncTask extends AsyncTask<String, Void, String> {
Activity activity;
Button button;
TextView textView;
IOException ioException;
MyAsyncTask(Activity activity, TextView textView, Button button) {
super();
this.activity = activity;
this.textView = textView;
this.button = button;
this.ioException = null;
}
#Override
protected String doInBackground(String... params) {
StringBuilder sb = new StringBuilder();
try {
Socket socket = new Socket(
params[0],
Integer.parseInt(params[1]));
OutputStream out = socket.getOutputStream();
out.write(params[2].getBytes());
InputStream in = socket.getInputStream();
byte buf[] = new byte[1024];
int nbytes;
while ((nbytes = in.read(buf)) != -1) {
sb.append(new String(buf, 0, nbytes));
}
socket.close();
} catch(IOException e) {
this.ioException = e;
return "error";
}
return sb.toString();
}
#Override
protected void onPostExecute(String result) {
if (this.ioException != null) {
new AlertDialog.Builder(this.activity)
.setTitle("An error occurrsed")
.setMessage(this.ioException.toString())
.setIcon(android.R.drawable.ic_dialog_alert)
.show();
} else {
this.textView.setText(result);
}
this.button.setEnabled(true);
}
}
}
On GitHub with build boilerplate.
I've also posted an Android server example at: https://stackoverflow.com/a/35745834/895245
Tested on Android 5.1.1, Sony Xperia 3 D6643.