FragNav

Android library for managing multiple stacks of fragments (e.g., Bottom Navigation , Navigation Drawer). This library does NOT include the UI for bottom tab bar layout. For that, I recommend either BottomBar (which is the library shown in the demo) or AHBottomNavigation. This library helps maintain order after pushing onto and popping from multiple stacks(tabs). It also helps with switching between desired tabs and clearing the stacks.

<img src="https://raw.githubusercontent.com/ncapdevi/FragNav/master/FragNavDemo.gif" width="30%" />

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Restrictions

Fragments are maintained in a stack per Android's guideline https://developer.android.com/guide/navigation/navigation-principles#navigation_state_is_represented_as_a_stack_of_destinations . A lot of questions get asked about how to maintain only one instance of a fragment, or to pull out a fragment in the middle of the stack. That is outside Android navigation guidelines, and also this library. You may want to rethink your UX.

Sample

With Material Design Bottom Navigation pattern, and other tabbed navigation, managing multiple stacks of fragments can be a real headache. The example file shows best practice for navigating deep within a tab stack.

Gradle

implementation 'com.ncapdevi:frag-nav:3.2.0'   //or or `compile` if on older gradle version

How do I implement it?

Initialize using a builder and one of two methods

    private val fragNavController: FragNavController = FragNavController(supportFragmentManager, R.id.container)

1.

Create a list of fragments and pass them in

 val fragments = listOf(
                RecentsFragment.newInstance(0),
                FavoritesFragment.newInstance(0),
                NearbyFragment.newInstance(0),
                FriendsFragment.newInstance(0),
                FoodFragment.newInstance(0),
                RecentsFragment.newInstance(0),
                FavoritesFragment.newInstance(0),
                NearbyFragment.newInstance(0),
                FriendsFragment.newInstance(0),
                FoodFragment.newInstance(0),
                RecentsFragment.newInstance(0),
                FavoritesFragment.newInstance(0))

fragNavController.rootFragments = fragments

2.

Allow for dynamically creating the base class by implementing the NavListener in your class and overriding the getRootFragment method

public class YourActivity extends AppCompatActivity implements FragNavController.RootFragmentListener {

fragNavController.rootFragmentListener = this

    override val numberOfRootFragments: Int = 5

    override fun getRootFragment(index: Int): Fragment {
        when (index) {
            INDEX_RECENTS -> return RecentsFragment.newInstance(0)
            INDEX_FAVORITES -> return FavoritesFragment.newInstance(0)
            INDEX_NEARBY -> return NearbyFragment.newInstance(0)
            INDEX_FRIENDS -> return FriendsFragment.newInstance(0)
            INDEX_FOOD -> return FoodFragment.newInstance(0)
        }
        throw IllegalStateException("Need to send an index that we know")
    }

3.

        fragNavController.initialize(FragNavController.TAB3, savedInstanceState)

SaveInstanceState

Send in the supportFragment Manager, a list of base fragments, the container that you'll be using to display fragments. After that, you have four main functions that you can use In your activity, you'll also want to override your onSaveInstanceState like so

    override fun onSaveInstanceState(outState: Bundle?) {
        super.onSaveInstanceState(outState)
        fragNavController.onSaveInstanceState(outState!!)

    }

Switch tabs

Tab switching is indexed to try to prevent you from sending in wrong indices. It also will throw an error if you try to switch to a tab you haven't defined a base fragment for.

fragNavController.switchTab(NavController.TAB1);

Push a fragment

You can only push onto the currently selected index

        fragNavController.pushFragment(FoodFragment.newInstance())

Pop a fragment

You can only pop from the currently selected index. This can throw an UnsupportedOperationException if trying to pop the root fragment

        fragNavController.popFragment();

Pop multiple fragments

You can pop multiple fragments at once, with the same rules as above applying. If the pop depth is deeper than possible, it will stop when it gets to the root fragment

       fragNavController.popFragments(3);

Replacing a fragment

You can only replace onto the currently selected index

        fragNavController.replaceFragment(Fragment fragment);

You can also clear the stack to bring you back to the base fragment

        fragNavController.clearStack();

You can also navigate your DialogFragments using

        showDialogFragment(dialogFragment);
        clearDialogFragment();
        getCurrentDialogFrag()

Transaction Options

All of the above transactions can also be done with defined transaction options. The FragNavTransactionOptions have a builder that can be used.

class FragNavTransactionOptions private constructor(builder: Builder) {
    val sharedElements: List<Pair<View, String>> = builder.sharedElements
    @FragNavController.Transit
    val transition = builder.transition
    @AnimRes
    val enterAnimation = builder.enterAnimation
    @AnimRes
    val exitAnimation = builder.exitAnimation
    @AnimRes
    val popEnterAnimation = builder.popEnterAnimation
    @AnimRes
    val popExitAnimation = builder.popExitAnimation
    @StyleRes
    val transitionStyle = builder.transitionStyle
    val breadCrumbTitle: String? = builder.breadCrumbTitle
    val breadCrumbShortTitle: String? = builder.breadCrumbShortTitle
    val allowStateLoss: Boolean = builder.allowStateLoss

Get informed of fragment transactions

Have your activity implement FragNavController.TransactionListener and you will have methods that inform you of tab switches or fragment transactions

A sample application is in the repo if you need to see how it works.

Fragment Transitions

Can be set using the transactionOptions

Restoring Fragment State

Fragments transitions in this library use attach()/detch() (http://daniel-codes.blogspot.com/2012/06/fragment-transactions-reference.html). This is a delibrate choice in order to maintain the fragment's lifecycle, as well as being optimal for memory. This means that fragments will go through their proper lifecycle https://developer.android.com/guide/components/fragments.html#Lifecycle . This lifecycle includes going through OnCreateView which means that if you want to maintain view states, that is outside the scope of this library, and is up to the indiviudal fragment. There are plenty of resources out there that will help you design your fragments in such a way that their view state can be restored https://inthecheesefactory.com/blog/fragment-state-saving-best-practices/en and there are libraries that can help restore other states https://github.com/frankiesardo/icepick

Special Use Cases

History & Back navigation between tabs

The reason behind this feature is that many of the "big" apps out there has a fairly similar approach for handling back navigation. When the user starts to tap the back button the current tab's fragments are being thrown away (FragNav default configuration does this too). The more interesting part comes when the user reaches the "root" fragment of the current tab. At this point there are several approaches that we can choose:

• Nothing happens on further back button taps - This is the default
• FragNav tracks "Tab History" and send a tab switch signal and we navigate back in history to the previous tab.

To use the history keeping mode you'll have to add extra parameters to the builder:

mNavController = FragNavController.newBuilder(...)
                ...
                .switchController(FragNavTabHistoryController.UNLIMITED_TAB_HISTORY, new FragNavSwitchController() {
                    @Override
                    public void switchTab(int index, @Nullable FragNavTransactionOptions transactionOptions) {
                        bottomBar.selectTabAtPosition(index);
                    }
                })
                .build();

Here first we have to choose between two flavors (see below for details), then we'll have to provide a callback that handles the tab switch trigger (This is required so that our UI element that also contain the state of the selected tab can update itself - aka switching the tabs always triggered by the application never by FragNav).

| UNLIMITED_TAB_HISTORY | UNIQUE_TAB_HISTORY | | :--------------------------------------: | :----------------------------------: | | | |

Show & Hide modes for fragment "replacement"

While having a good architecture and caching most of the data that is presented on a page makes attaching / detaching the fragments when switching pretty seamless there may be some cases wher