How to pass arguments to a fragment using bottom navigation view and Android Navigation component?

问题

Is it possible to pass and access arguments in a fragment using a bottom navigation view and the Navigation component?

I'm using a one activity with many fragments approach where my top level fragment requires an argument(Usually done via the newInstance generated method). I've had a look at the Navigation component developer guide and the codelab but it only mentions using safeargs and adding argument tags in the destinations and actions.

Here's my navigation graph:

<navigation xmlns:app="http://schemas.android.com/apk/res-auto" 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" 
    app:startDestination="@id/homeFragment">

    <fragment android:id="@+id/homeFragment"
          android:name="uk.co.homeready.homeready.HomeFragment"
          android:label="fragment_home"
          tools:layout="@layout/fragment_home">
          <!--Do I create an argument block here?-->
    </fragment>

    <fragment android:id="@+id/calculatorFragment"
          android:name="uk.co.homeready.homeready.CalculatorFragment"
          android:label="fragment_calculator"
          tools:layout="@layout/fragment_calculator"/>

    <fragment android:id="@+id/resourcesFragment"
          android:name="uk.co.homeready.homeready.ResourcesFragment"
          android:label="fragment_resources"
          tools:layout="@layout/fragment_resources"/>

</navigation>

Bottom Navigation View menu:

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

    <item
        android:id="@+id/homeFragment"
        android:icon="@drawable/ic_home_black_24dp"
        android:title="@string/title_home"/>

    <item
        android:id="@+id/calculatorFragment"
        android:icon="@drawable/ic_baseline_attach_money_24px"
        android:title="@string/title_calculator"/>

    <item
        android:id="@+id/resourcesFragment"
        android:icon="@drawable/ic_baseline_library_books_24px"
        android:title="@string/title_resources"/>

</menu>

MainActivity:

override fun onCreate(savedInstanceState: Bundle?) {
        ...
        val navController = Navigation.findNavController(this, 
        R.id.nav_host_fragment)
        bottom_navigation.setupWithNavController(navController)
        ....
}

activity_main.xml

<android.support.constraint.ConstraintLayout>
    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        app:layout_constraintBottom_toTopOf="@id/bottom_navigation"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph"/>

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/bottom_navigation"
        app:menu="@menu/bottom_navigation"/>

</android.support.constraint.ConstraintLayout>

HomeFragment

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    val argument = //TODO access argument here
    ...
}

回答1:

If I understood you correctly, you want to pass arguments to destinations that is tied to menu items. Try to use 'OnDestinationChangedListener' inside your activity onCreate method, something like this:

navController.addOnDestinationChangedListener { controller, destination, arguments ->
        when(destination.id) {
            R.id.homeFragment -> {
                val argument = NavArgument.Builder().setDefaultValue(6).build()
                destination.addArgument("Argument", argument)
            }
        }
    }

Update:

If you want that your start destination will receive default arguments the implementation should be different. First, remove 'app:navGraph="@navigation/nav_graph"' from your 'NavHostFragment' xml tag.

Then, inside your activity onCreate you need to inflate the graph:

 val navInflater = navController.navInflater
 val graph = navInflater.inflate(R.navigation.nav_graph)

Then add your arguments to graph(this arguments will be attached to start destination)

val navArgument1=NavArgument.Builder().setDefaultValue(1).build()           
val navArgument2=NavArgument.Builder().setDefaultValue("Hello").build()
graph.addArgument("Key1",navArgument1)
graph.addArgument("Key2",navArgument2)

Then attach the graph to NavController:

navController.graph=graph

Now your first destination should receive the attached arguments.

回答2:

The correct way to do this is indeed with an <argument> block on your destination.

<fragment android:id="@+id/homeFragment"
      android:name="uk.co.homeready.homeready.HomeFragment"
      android:label="fragment_home"
      tools:layout="@layout/fragment_home">
      <argument
          android:name="Argument"
          android:defaultValue="value"
          />
</fragment>

This will automatically populate the arguments of the Fragment with the default value without any additional code needed. As of Navigation 1.0.0-alpha09, this is true whether you use the Safe Args Gradle Plugin or not.

回答3:

Default values was not usable for me, because I have dynamic menu items that could have multiple of the same destination with different arguments. (changed from server)

Implement BottomNavigationView.OnNavigationItemSelectedListener:

override fun onNavigationItemSelected(item: MenuItem): Boolean {
    val fragmentId = item.itemId
    val arguments = argumentsByFragmentId[fragmentId] // custom mutableMapOf<Int, Bundle?>() with arguments
    navController().navigate(fragmentId, arguments)
    return true
}

To use that you will takeover the navigation, by replacing the listener. The order of calls here are important:

bottomNavigationView.setupWithNavController(navController)
bottomNavigationView.setOnNavigationItemSelectedListener(this)

来源：https://stackoverflow.com/questions/54082036/how-to-pass-arguments-to-a-fragment-using-bottom-navigation-view-and-android-nav