How to run a timer in the background ?

Problem :- When you switch fragment and come back to Timer Fragment, the onCreate lifecycle callback will be called and that gone reset your timer in

customHandler.postDelayed(updateTimerThread, 0);

Solution :- Move timer logic to Activity class but activity will be recreate in orientation change so move timer logic into Application class :-

Drop this class in you project package

import java.text.SimpleDateFormat;
import java.util.Date;

import android.app.Application;
import android.os.Handler;
import android.widget.Toast;

public class App extends Application {

    public static App appInstance;
    private SimpleDateFormat dateFormat;

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

        appInstance = this;

        dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
    }

    public void afficher() {
        Toast.makeText(getBaseContext(), dateFormat.format(new Date()), 300).show();
        handler.postDelayed(runnable,1000);
    }

    public void startTimer() {
        runnable.run();
    }

    public void stopTimer() {
        handler.removeCallbacks(runnable);
    }

    Handler handler = new Handler();
    Runnable runnable = new Runnable() {
        public void run() {
            afficher();
        }
    };

}

Set your Application name to App class like this below (android name property of application) :-

   <application
        android:name="com.masterdetail_webview.App"
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.masterdetail_webview.TimertestActivity"
            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>

Now you can start and stop timer simply like this from anywhere

findViewById(R.id.button1).setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            App.appInstance.startTimer();

        }
    });

    findViewById(R.id.button2).setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            App.appInstance.stopTimer();

        }
    });

Adding AppController