Android: Is it better to create a new fragment eve

Question

I am implementing the standard navigation drawer pattern for android, with about 10 fragments the user can navigate to from the drawer. Currently, I am creating a new Fragment every time a different navigation drawer item is clicked like so:

// When a new navigation item at index is clicked 
FragmentTransaction ft = fragmentManager.beginTransaction();
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
Fragment newFragment = null;
if (index == 0)
    fragment = new Fragment0();
...
ft.replace(R.id.container, newFragment);
ft.commit();

I have been wondering if it would be more efficient to do something like the following:

// Somewhere in onCreate
Fragment[] fragments = new Fragment[n];
fragments[0] = new Fragment0();
fragments[1] = new Fragment1();
...

// When a new navigation item (at index) is clicked 
FragmentTransaction ft = fragmentManager.beginTransaction();
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.replace(R.id.container, fragments[index]);
ft.commit();

My main worry is that some of the fragments hold a significant amount of data (fairly large lists and lots of views). Would there be any issue holding all these fragments in memory and would it provide any advantage over instantiating new fragments every time (apart from faster switches between fragments)? Is there a generally accepted 'better' solution?

Answer 1

I had a similar issue. I took an approach similar to yours, and to save load on processor I made the following tweak to every call to create an instance for a Fragment object: (in context to my use in selectItem method)

switch (position) {
    case 0:
        if (fragmentOne == null)
            fragmentOne = new FragmentOne();
        getSupportFragmentManager().beginTransaction().......
        break;
    case 1:
        if (fragmentTwo == null)
            fragmentTwo = new FragmentTwo();
        getSupportFragmentManager()......

FragmentOne and FragmentTwo are the two different Fragment classes and fragmentOne and fragmentTwo are their objects declared as fields in MainActivity

Edit:

I would like to add how you could follow a similar approach with the array holding the fragments. Instead of creating new fragments in onCreate, do that when an item is clicked. In onCreate, send a call to the drawer to select the fragment which you want selected by default on launch.

//somewhere in onCreate
if (savedInstanceState == null) {
    selectItem(defaultFragment);
}
else
    selectItem(selectedFragment);
//selectItem is method called by DrawerItemClickListener as well


//in selectItem: when navigation item at index is clicked, the listener calls this
switch (index) {
    case 0:
        if (fragments == null) {
            fragments = new Fragment[n];
            fragment[0] = new Fragment0();
        }
        else if (fragments[0] == null) {
            fragments[0] = new Fragment0();
        }
        break;
    ....
}
FragmentTransaction ft = fragmentManager.beginTransaction();
...
ft.replace(R.id.container, fragments[index]);
ft.commit();

No need to instantiate the fragments on onCreate since that makes the startup slow. Create them as and when needed and afterwards use the same one if it exists. The new fragments are created only if they are being loaded for the first time.