In Jetpack navigation, how to know which action trigger my fragment

Question

With Jetpack navigation, I have Fragment A->B->C->B, For fragment B's onCreate, How to check B come from A or back from C.

Answer 1

You have to pass some data from framgent A->B or C->B.

As Example you can send integer value, or string or any other according to your requirement. I'm using integer for example

<fragment
android:id="@+id/flow_step_one_dest"
android:name="com.example.android.codelabs.navigation.FlowStepFragment"
tools:layout="@layout/flow_step_one_fragment">
<argument
    android:name="flowStepNumber"
    app:argType="integer"
    android:defaultValue="1"/>

<action...>
</action>

and Fragment A and C you can pass value like this

val flowStepNumberArg = 1
val action = FragmentADirections.nextAction(flowStepNumberArg) //For Fragment A
//val action = FragmentCDirections.nextAction(flowStepNumberArg) //For Fragment C
findNavController().navigate(action)

and inside Fragment B you can retrieve by this:

val safeArgs: FlowStepFragmentArgs by navArgs()
val flowStepNumber = safeArgs.flowStepNumber

If you have not added dependencies for safeArgs than you can add it to project level build.gradle

dependencies {
    classpath "androidx.navigation:navigation-safe-args-gradle-plugin:$navigationVersion"
//...
}

And in app level build.gradle at top add this line

apply plugin: 'androidx.navigation.safeargs.kotlin'

If you need more understanding than check out Google's Codelab