Tukukkk

My app works like a Wizard. I have an Activity that serves as a centralization for all my fragments. There is a BottomNavigationView with a "Next" button that appears in each fragment to drive the wizard.

When I want to go next I call "action_next" from BottomNavMenu and it navigate to the next fragment.

But I need to perform some action's when the user presses the Next Button in the context of that fragment (like store the data inputted). Further, I need to cancel the navigation if there is any problem with data inputted by the user.

At first try i did this in my fragment:

val controller = NavHostFragment.findNavController(this)



        controller.addOnNavigatedListener { controller, navDestination: NavDestination ->



            when (navDestination.id) {

                R.id.destination_setup_tournment -> {

                    proceedNavigation(controller, navDestination)



                }



            }

        }





private fun proceedNavigation(controller: NavController, navDestination: NavDestination) {

    val teams = teamAdapter.getItems()

    if (validateSubmit(teams)){

        presenter.saveTeams(teams)

    }else{

        //how to cancel navigation and stay on this fragment?

    }

}

But it does not look good or even correct for me and I don't know how to cancel the navigation if something is wrong.

Here is the App's related files:

MainActivity:

<androidx.appcompat.widget.Toolbar

    android:id="@+id/toolbar"

    android:layout_width="match_parent"

    android:layout_height="wrap_content"

    android:background="?colorPrimary"

    android:theme="@style/ToolbarTheme" />



<fragment

    android:id="@+id/nav_host_fragment"

    android:layout_width="match_parent"

    android:layout_height="0dp"

    android:layout_weight="1"

    android:name="androidx.navigation.fragment.NavHostFragment"

    app:navGraph="@navigation/navigation"

    app:defaultNavHost="true" />

<com.google.android.material.bottomnavigation.BottomNavigationView

    android:id="@+id/bottom_nav_view"

    android:layout_width="match_parent"

    android:layout_height="wrap_content"

    android:layout_gravity="bottom"

    app:menu="@menu/bottom_nav"

    style="@style/Widget.MaterialComponents.BottomNavigationView"

    >





</com.google.android.material.bottomnavigation.BottomNavigationView>

bottom_nav.xml:

<?xml version="1.0" encoding="utf-8"?>

<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:id="@+id/action_next" android:title="@string/tornment_mode" android:icon="@drawable/ic_navigate_next_black_24dp" />



</menu>

There's no way to 'cancel' a navigation event - you need to put your business logic on your button/listener itself and only call navigate() when you actually want to navigate.

The Creating event callbacks to the activity documentation goes over one approach for connecting your Activity and Fragment together by using onAttach(Context) to get a reference to your Activity and set a property, callback, etc.

For example, you might consider doing something like:

// In your Activity

var onNextClicked: () -> Unit = {}



// In your Activity's onCreate()

button.setOnClickListener = View.OnClickListener {

  onNextClicked.invoke()

}



// In your Fragment

override fun onAttach(context: Context) {

  (context as YourActivity).onNextClicked = {

    val teams = teamAdapter.getItems()

    if (validateSubmit(teams)){

      presenter.saveTeams(teams)

      findNavController().navigate(R.id.action_next)

    }

  }

}

Each Fragment would set what they want the next button to do, allowing you full control over what the button does.

If you're dead set on the BottomNavigationView instead of just using an actual Button, you'd want to set your own OnNavigationItemSelectedListener and have that listener call the onNextClicked lambda if you're using this example.