Question

in my android application I have a socket, but when I rotate the screen, I have to keep the socket connected, to send messages to a server. So I decided to do this:

package pfg.nao.naoControler;

import java.io.IOException;

import java.net.Socket;

import java.net.UnknownHostException;

import android.app.Application;

public class clientSocket extends Application{

public Socket clientSocket;

@Override
public void onCreate() 
{
    super.onCreate();
}

public void setSocket(Socket socket) throws UnknownHostException, IOException{

    clientSocket = socket;
}

public Socket getSocket() throws UnknownHostException, IOException{

    return clientSocket;
}

}

A global socket to use it in my activities and threads. Because I have to be able to open and close the connection in some cases.

For example, I try to access to clientSocket like this:

Socket c = new Socket(IP, puerto);
((clientSocket)this.getApplication()).setSocket(c);

But I have this error:

06-24 22:25:18.217: E/AndroidRuntime(25267): FATAL EXCEPTION: main
06-24 22:25:18.217: E/AndroidRuntime(25267): java.lang.ClassCastException: android.app.Application
06-24 22:25:18.217: E/AndroidRuntime(25267):    at pfg.nao.naoControler.NaoControlerActivity.onOptionsItemSelected(NaoControlerActivity.java:160)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at android.app.Activity.onMenuItemSelected(Activity.java:2312)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at com.android.internal.policy.impl.PhoneWindow.onMenuItemSelected(PhoneWindow.java:769)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:143)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:855)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at com.android.internal.view.menu.IconMenuView.invokeItem(IconMenuView.java:532)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at com.android.internal.view.menu.IconMenuItemView.performClick(IconMenuItemView.java:122)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at android.view.View$PerformClick.run(View.java:9262)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at android.os.Handler.handleCallback(Handler.java:587)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at android.os.Handler.dispatchMessage(Handler.java:92)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at android.os.Looper.loop(Looper.java:130)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at android.app.ActivityThread.main(ActivityThread.java:3744)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at java.lang.reflect.Method.invokeNative(Native Method)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at java.lang.reflect.Method.invoke(Method.java:507)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at  com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
06-24 22:25:18.217: E/AndroidRuntime(25267):    at dalvik.system.NativeStart.main(Native Method)

Here it is my android manyfest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="pfg.nao.naoControler"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk
    android:minSdkVersion="7"
    android:targetSdkVersion="8" />

<uses-permission android:name="android.permission.INTERNET" >
</uses-permission>

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name" >
    <activity
        android:name=".NaoControlerActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name=".SettingsActivity"
        android:label="@string/settings" >
    </activity>
</application>
<application
    android:name=".clientSocket"
    android:label="@string/cliente" >
</application>

</manifest>

Thanks!

Answer 1

What I’d probably do (just based on the info you’ve given) is make the Socket accessible via static method. This way you don’t have to worry about whether or not the Application is initialized, or if you’re calling the right Application object.

Something like this (renamed a couple things to avoid confusion…):

public class clientSocket extends Application {
    private static Socket localSocket;

    @Override
    public void onCreate() {
        super.onCreate();
    }

    public static void setSocket(Socket socket) throws UnknownHostException, IOException {
        localSocket = socket;
    }

    public static Socket getSocket() throws UnknownHostException, IOException {
        // Check here if it's null; if it is, then initialize it, or throw some exception, or something.
        return localSocket;
    }
}

Then, you can initialize it like this:

Socket c = new Socket(IP, puerto);
clientSocket.setSocket(c);

And you can call it like this:

Socket c = clientSocket.getSocket();

Keep in mind: this method will only work if you have just one Socket that you are sharing between classes. If you have multiple, you would have to array them, have multiple classes (with their own Sockets), or multiple static Socket objects in your class.