Question

I am trying to create a tablet application with fragments. The left part of the screen will have four buttons and the right part of the screen will change depending on what button was clicked.
I have created main activity and four fragments. Each fragment has its own layout with several TextView fields. When applications starts it loads all fragments to RAM – this way it can keep the fragments status so that when user switch from one fragment to another all the text fields keep their text values until he clicks the final submit button. The app is based on SDK 4.1. The app is a little bit slow especially when it starts. I was wondering if it has been designed properly and if there are some way to improve it?

Below is the main activity class:

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {

    private Button buttonOne;
    private Button buttonTwo;
    private Button buttonThree;
    private Button buttonFour;

    private Fragment fragmentOne;
    private Fragment fragmentTwo;
    private Fragment fragmentThree;
    private Fragment fragmentFour;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        buttonOne = (Button) findViewById(R.id.button_one);
        buttonTwo = (Button) findViewById(R.id.button_two);
        buttonThree = (Button) findViewById(R.id.button_three);
        buttonFour = (Button) findViewById(R.id.button_four);

        fragmentOne = new FragmentOne();
        fragmentTwo = new FragmentTwo();
        fragmentThree = new FragmentThree();
        fragmentFour = new FragmentFour();

        FragmentTransaction fragmentTransaction = getFragmentManager()
                .beginTransaction();

        fragmentTransaction.add(R.id.frameLayout_one, fragmentOne);
        fragmentTransaction.add(R.id.frameLayout_one, fragmentTwo);
        fragmentTransaction.add(R.id.frameLayout_one, fragmentThree);
        fragmentTransaction.add(R.id.frameLayout_one, fragmentFour);

        fragmentTransaction.commit();

        buttonOne.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {

                FragmentTransaction fragmentTransaction = getFragmentManager()
                        .beginTransaction();
                fragmentTransaction.show(fragmentOne);
                fragmentTransaction.hide(fragmentTwo);
                fragmentTransaction.hide(fragmentThree);
                fragmentTransaction.hide(fragmentFour);

                fragmentTransaction.commit();

            }
        });

        buttonTwo.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {

                FragmentTransaction fragmentTransaction = getFragmentManager()
                        .beginTransaction();
                fragmentTransaction.hide(fragmentOne);
                fragmentTransaction.show(fragmentTwo);
                fragmentTransaction.hide(fragmentThree);
                fragmentTransaction.hide(fragmentFour);

                fragmentTransaction.commit();

            }
        });
        buttonThree.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {

                FragmentTransaction fragmentTransaction = getFragmentManager()
                        .beginTransaction();
                fragmentTransaction.hide(fragmentOne);
                fragmentTransaction.hide(fragmentTwo);
                fragmentTransaction.show(fragmentThree);
                fragmentTransaction.hide(fragmentFour);

                fragmentTransaction.commit();

            }
        });
        buttonFour.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {

                FragmentTransaction fragmentTransaction = getFragmentManager()
                        .beginTransaction();
                fragmentTransaction.hide(fragmentOne);
                fragmentTransaction.hide(fragmentTwo);
                fragmentTransaction.hide(fragmentThree);
                fragmentTransaction.show(fragmentFour);

                fragmentTransaction.commit();

            }
        });

    }

Answer 1

Consider using a FragmentStateViewPager.

In an ideal world, if you have several Fragments you are switching between like in your case, you’ll probably not want to keep them around in RAM. 2 or 3 fragments is probably okay, 4 or more is starting to push it.

The FragmentStateViewPager will automatically detach and save the state of your Fragments as they move “off screen”

You will have to implement onSaveInstanceState in each one of your fragments to save any state of any non-UI member variables (UI Views save their state automagically). Then restore them in onCreate or onCreateView.

*Of course, if your Fragments’ onCreate/onCreateViews are slow, then this won’t help much. First make sure your Fragments’ creations are fast… Start by looking for code that can be moved from onCreate/onCreate view to onResume.