i am pretty new to android and java programming. I am programming a server client connection. My PC shall be the server and my android smartphone shall be the client. The server works great. I can send a message from the client to the server, but I can’t send a message from the server to the client. When i am doing this the client crushes and closes itself. I really hope that anybody can help me with my big issue.
Here is my Activity:
package com.example.sercerclient2zweidreidrei;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MyActivity extends Activity {
Button btn;
EditText textOut;
TextView textIn;
TextView problems;
Button send;
private TCPClient myTcpClient;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
final EditText editText = (EditText) findViewById(R.id.editText);
final TextView textIn = (TextView) findViewById(R.id.textin);
Button send = (Button)findViewById(R.id.send_button);
// connect to the server
new connectTask().execute("");
send.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String message = editText.getText().toString();
//sends the message to the server
if (myTcpClient != null) {
myTcpClient.sendMessage(message);
}
}
});
}
public class connectTask extends AsyncTask<String,String,TCPClient> {
@Override
protected TCPClient doInBackground(String... message) {
//we create a TCPClient object and
myTcpClient = new TCPClient(new TCPClient.OnMessageReceived() {
@Override
//here the messageReceived method is implemented
public void messageReceived(String message) {
//this method calls the onProgressUpdate
publishProgress(message);
}
});
myTcpClient.run();
return null;
}
@Override
protected void onProgressUpdate(String... values) {
super.onProgressUpdate(values);
//in the arrayList we don't add the message received from server
//here i try to write the incomming message into a textVie
textIn.setText(values[0]);
}
}
}
and here is my TCPClient class:
package com.example.sercerclient2zweidreidrei;
import android.util.Log;
import java.io.*;
import java.net.InetAddress;
import java.net.Socket;
public class TCPClient {
private String serverMessage;
public static final String SERVERIP = "192.168.2.107"; //your computer IP address
public static final int SERVERPORT = 4444;
private OnMessageReceived mMessageListener = null;
private boolean mRun = false;
PrintWriter out;
BufferedReader in;
/**
* constructor of the class. OnMessageReceived listens for the messages
* received from server
*/
public TCPClient(OnMessageReceived listener) {
mMessageListener = listener;
}
/**
* Sends the message entered by client to the server
* @param message text entered by client
*/
public void sendMessage(String message){
if (out != null && !out.checkError()) {
out.println(message);
out.flush();
}
}
public void stopClient() {
mRun = false;
}
public void run() {
mRun = true;
try {
// here you must put your computer's IP address.
InetAddress serverAddr = InetAddress.getByName(SERVERIP);
Log.e("TCP Client", "C: Connecting...");
//create a socket to make the connection with the server
Socket socket = new Socket(serverAddr, SERVERPORT);
try {
//send the message to the server
out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())), true);
Log.e("TCP Client", "C: Sent.");
Log.e("TCP Client", "C:Done.");
//receive the message which the server sends back
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
//in this while the client listens for the messages send by the server
while (mRun) {
serverMessage = in.readLine();
if (serverMessage != null && mMessageListener != null) {
//call the method messageReceived from MyActivity class
mMessageListener.messageReceived(serverMessage);
}
serverMessage = null;
}
Log.e("RESPONSE FROM SERVER", "S: Received Message: '" + serverMessage + "'");
} catch (Exception e) {
Log.e("TCP", "S: Error", e);
} finally {
//the socket must be closed. It is not possible to reconnect to this socket
//after it is closed, which means a new socket instance has to be created.
socket.close();
}
} catch (Exception e) {
Log.e("TCP", "C:Error", e);
}
}
/*
* Declare the interface. The method messageReceived(String message must be
* implemented in the MyActivity class at on asynckTask doInBackground
*/
public interface OnMessageReceived {
public void messageReceived(String message);
}
}
Finally here you can see my main.xml
<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=".MyActivity" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:text="@string/Textausgabe" />
<EditText
android:id="@+id/editText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/textView1"
android:layout_marginTop="34dp"
android:ems="10" >
<requestFocus />
</EditText>
<Button
android:id="@+id/send_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignRight="@+id/textView1"
android:layout_below="@+id/editText"
android:layout_marginTop="26dp"
android:text="@string/Senden" />
<TextView
android:id="@+id/textin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:text="@string/EinkommenderText"
android:textAppearance="?android:attr/textAppearanceLarge" />
</RelativeLayout>
Here is my LogCat:
12-30 16:36:37.340: I/dalvikvm(548): threadid=3: reacting to signal 3
12-30 16:36:37.560: I/dalvikvm(548): Wrote stack traces to ‘/data/anr/traces.txt’
12-30 16:36:37.740: I/dalvikvm(548): threadid=3: reacting to signal 3
12-30 16:36:37.790: I/dalvikvm(548): Wrote stack traces to ‘/data/anr/traces.txt’
12-30 16:36:38.350: D/gralloc_goldfish(548): Emulator without GPU emulation detected.
12-30 16:36:38.630: I/dalvikvm(548): threadid=3: reacting to signal 3
12-30 16:36:38.650: I/dalvikvm(548): Wrote stack traces to ‘/data/anr/traces.txt’
12-30 16:36:39.721: E/TCP Client(548): C: Connecting…
12-30 16:36:39.981: E/TCP Client(548): C: Sent.
12-30 16:36:39.990: E/TCP Client(548): C:Done.
12-30 16:38:59.034: D/AndroidRuntime(548): Shutting down VM
12-30 16:38:59.034: W/dalvikvm(548): threadid=1: thread exiting with uncaught exception
(group=0x409c01f8)12-30 16:38:59.051: E/AndroidRuntime(548): FATAL EXCEPTION: main
12-30 16:38:59.051: E/AndroidRuntime(548): java.lang.NullPointerException
12-30 16:38:59.051: E/AndroidRuntime(548): at
com.example.sercerclient2zweidreidrei.MyActivity$connectTask.onProgressUpdate(MyActivity.java:72)12-30 16:38:59.051: E/AndroidRuntime(548): at
com.example.sercerclient2zweidreidrei.MyActivity$connectTask.onProgressUpdate(MyActivity.java:1)12-30 16:38:59.051: E/AndroidRuntime(548): at
android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:618)12-30 16:38:59.051: E/AndroidRuntime(548): at
android.os.Handler.dispatchMessage(Handler.java:99)12-30 16:38:59.051: E/AndroidRuntime(548): at android.os.Looper.loop(Looper.java:137)
12-30 16:38:59.051: E/AndroidRuntime(548): at
android.app.ActivityThread.main(ActivityThread.java:4424)12-30 16:38:59.051: E/AndroidRuntime(548): at
java.lang.reflect.Method.invokeNative(Native Method)12-30 16:38:59.051: E/AndroidRuntime(548): at
java.lang.reflect.Method.invoke(Method.java:511)12-30 16:38:59.051: E/AndroidRuntime(548): at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)12-30 16:38:59.051: E/AndroidRuntime(548): at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)12-30 16:38:59.051: E/AndroidRuntime(548): at dalvik.system.NativeStart.main(Native
Method)12-30 16:38:59.752: I/dalvikvm(548): threadid=3: reacting to signal 3
12-30 16:38:59.900: I/dalvikvm(548): Wrote stack traces to ‘/data/anr/traces.txt’
I hope you can find my mistake.
You use an AsyncTask task in an Activity to establish a TCP connection. So as soon as the connection is established the message is sent and your AsyncTask task finishes and you close the TCP connection.
You should use a stand-alone service instead of an Activity to keep the connection open.