The idea is to start a chat. So I have this properties in my class:
private MulticastSocket so;
private EditText messageBoard;
private InetAddress serverAddress;
private int port;
Then I have this code in the onCreate() method:
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.second);
// connect to server
connect();
// Associate a variable with the Button on the interface
final Button sendButton = (Button) findViewById(R.id.button2);
sendButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// when the button is clicked the next screen is loaded
sendMessage();
}
});
} // end of onCreate
Here is my connect() method:
private void connect() {
port = 4456;
// convert the host name to InetAddress
try {
serverAddress = InetAddress.getByName("my server address is here");
} catch (Exception e) {}
// create socket and start communicating
try {
so = new MulticastSocket(port);
so.joinGroup(serverAddress);
} catch (IOException e) {}
// start listening for incoming messages
new Receiver(so, messageBoard);
}
Everything looks right to me but this is what it says:
01-24 23:33:16.277: W/dalvikvm(569): threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
01-24 23:33:16.357: E/AndroidRuntime(569): FATAL EXCEPTION: main
01-24 23:33:16.357: E/AndroidRuntime(569): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.regeduser00x.proj1/com.regeduser00x.proj1.Second}: android.os.NetworkOnMainThreadException
01-24 23:33:16.357: E/AndroidRuntime(569): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
01-24 23:33:16.357: E/AndroidRuntime(569): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
01-24 23:33:16.357: E/AndroidRuntime(569): at android.app.ActivityThread.access$600(ActivityThread.java:123)
01-24 23:33:16.357: E/AndroidRuntime(569): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
01-24 23:33:16.357: E/AndroidRuntime(569): at android.os.Handler.dispatchMessage(Handler.java:99)
01-24 23:33:16.357: E/AndroidRuntime(569): at android.os.Looper.loop(Looper.java:137)
01-24 23:33:16.357: E/AndroidRuntime(569): at android.app.ActivityThread.main(ActivityThread.java:4424)
01-24 23:33:16.357: E/AndroidRuntime(569): at java.lang.reflect.Method.invokeNative(Native Method)
01-24 23:33:16.357: E/AndroidRuntime(569): at java.lang.reflect.Method.invoke(Method.java:511)
01-24 23:33:16.357: E/AndroidRuntime(569): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-24 23:33:16.357: E/AndroidRuntime(569): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-24 23:33:16.357: E/AndroidRuntime(569): at dalvik.system.NativeStart.main(Native Method)
01-24 23:33:16.357: E/AndroidRuntime(569): Caused by: android.os.NetworkOnMainThreadException
01-24 23:33:16.357: E/AndroidRuntime(569): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099)
01-24 23:33:16.357: E/AndroidRuntime(569): at java.net.InetAddress.lookupHostByName(InetAddress.java:391)
01-24 23:33:16.357: E/AndroidRuntime(569): at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)
01-24 23:33:16.357: E/AndroidRuntime(569): at java.net.InetAddress.getByName(InetAddress.java:295)
01-24 23:33:16.357: E/AndroidRuntime(569): at com.regeduser00x.proj1.Second.connect(Second.java:99)
01-24 23:33:16.357: E/AndroidRuntime(569): at com.regeduser00x.proj1.Second.onCreate(Second.java:38)
01-24 23:33:16.357: E/AndroidRuntime(569): at android.app.Activity.performCreate(Activity.java:4465)
01-24 23:33:16.357: E/AndroidRuntime(569): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-24 23:33:16.357: E/AndroidRuntime(569): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
01-24 23:33:16.357: E/AndroidRuntime(569): ... 11 more
That Second.java:99 happens to be serverAddress = InetAddress.getByName("my server address is here"); and line 38 happens to be connect(); What's the matter with it? I have tested the line with the InetAddress in a small test program and it works perfectly but here something happens.
this line:
Caused by: android.os.NetworkOnMainThreadException
Tells you what is going on.
You are attempting to access a network function on the Main(UI) thread. starting with Honeycomb the system raises an Exception when you do this.
To fix you just need to move any thing that is touching the network to its own thread.
This is done to make sure you do not block the UI thread from handling any input events from the user.By blocking the UI thread your application cannot perform any event handling routines.
Normally most UI systems have a watchdog timer,which keeps watching for any long operation on the UI thread and if the UI thread is blocked for more than a threshold(probably 10-20 seconds in android devices varying by manufacturer/OS version) the watchdog interrupts and causes a 'Application Not responding'(a.k.a ANR) to pop-up.
If you just want an easy work-around this, specify a minimum SDK version of Froyo or Gingerbread and omit the targetSdkVersion:
android:minSdkVersion="8"
来源：https://stackoverflow.com/questions/8995364/strange-networkonmainthreadexception-in-android-app