Pass data/bundle using navigateUp in Android Navigation Component

Question

I found the question but does not have solution in code

I want to have data when backpress/manual back happens. I am using navigateUp() to go back. How

Answer 1

You should use static variables/companion objects, because it is better than shared viewmodel as it is not simple/nice architecture. As it it not straightforward, I think it is the best way.

To navigateUp From FragmentB to FragmentA

FragmentB:

isBackpressed = true
findNavController().navigateUp() 

FragmentA:

onViewCreated() {
    // todo
    if(isBackpressed) {
         isBackpressed = false
         // do whatever you want
    }
}

Answer 2

According to developer.android.com, you can use common for fragments where you want to share data ViewModel using their activity scope.

Here are steps:

1. Create view model which will keep the data:

class SharedViewModel : ViewModel() {
    val dataToShare = MutableLiveData<String>()

    fun updateData(data: String) {
        dataToShare.value = data
    }
}

2. Observe data changes in Fragment1:

class Fragment1 : Fragment() {

    private lateinit var viewModel: SharedViewModel

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        viewModel = ViewModelProviders.of(activity!!).get(SharedViewModel::class.java)
        viewModel.dataToShare.observe(this, Observer<String> { dataFromFragment2 ->
            // do something with data
        })
    }
}

3. Update data in Fragment2 and if you're handling navigation properly, now, you should be able to receive data changes on Fragment1:

class Fragment2 : Fragment() {

    private lateinit var viewModel: SharedViewModel

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        viewModel = ViewModelProviders.of(activity!!).get(SharedViewModel::class.java)

        updateDataButton.setOnClickListener { v ->
            viewModel.updateData("New data for fragment1")
        }
    }
}

I hope answer helps.

Answer 3

You can use NavigationResult library. Basically it's startActivityForResult but for Fragments in Navigation component.

Answer 4

You can just call

findNavController().navigate(R.id.fragment1, args)

where args is your bundle. In fragment1, fetch the data from the arguments

Answer 5

You can use the following simple implementation to pass data after popBackStack() with Android Navigation Component. This approach is based on official Google documentation

You just need to extend your fragments with BaseFragment and use the following methods:

//to start Fragment2 for result
startFragmentForResult(actionId: Int)

//to perform pop back stack in Fragment2
popBackStackWithResult(result: Any)

//to observe your result in Fragment1
onFragmentResult(result: Any)

1. Add SharedViewModel class

   class SharedViewModel : ViewModel() {
       val sharedData = MutableLiveData<Any>()
   
       fun share(obj: Any) {
           sharedData.value = obj
       }
   }
   

2. Add BaseFragment class

   import androidx.fragment.app.Fragment
   
   abstract class BaseFragment : Fragment() {
   
   protected var rootView: View? = null
   
   private var sharedViewModel: SharedViewModel? = null
   
   override fun onCreateView(
       inflater: LayoutInflater,
       container: ViewGroup?,
       savedInstanceState: Bundle?
   ): View? {
       if (rootView == null) {
           rootView = inflater.inflate(getLayoutId(), container, false)
           initSharedViewModel()
       }
       return rootView
   }
   
   abstract fun getLayoutId()
   
   open fun onFragmentResult(result: Any){
       //TODO implement in descendants
   }
   
   protected fun startFragmentForResult(actionId: Int){
       findNavController().navigate(actionId)
   }
   
   protected fun popBackStackWithResult(result: Any){
       findNavController().popBackStack()
       sharedViewModel?.share(result)
   }
   
   private fun initSharedViewModel() {
       sharedViewModel = ViewModelProvider(activity!!).get(SharedViewModel::class.java)
   
       sharedViewModel?.sharedData?.observe(activity!!, object : Observer<Any> {
           override fun onChanged(params: Any) {
               onFragmentResult(params)
           }
       })
   }    
   }
   

3. Add Fragment1

   class Fragment1 : BaseFragment(){
       override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
           super.onViewCreated(view, savedInstanceState)
   
           some_btn.setOnClickListener{
               startFragmentForResult(R.id.action_fragment1_to_fragment2)
           }
       }
   
       override fun onFragmentResult(result: Any) {
           if(result is AnyYourClass){
               //PERFECT! DO SOMETHING WITH YOUR RESULT
           }
       }
   }
   

4. Add Fragment2

   class Fragment2 : BaseFragment(){
       override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
           super.onViewCreated(view, savedInstanceState)
   
           some_btn.setOnClickListener{
               popBackStackWithResult(AnyYourClass())
           }
       }            
   }
   

Cheers ;)

Answer 6

To pop destinations when navigating from one destination to another, add an app:popUpTo attribute to the associated <action> element. To navigate from fargment2 to Fragment1 with arguments, specify in the navigation graph the action of the caller fragment and the arguments of the destination fragment :

<fragment
    android:id="@+id/fragment2"
    android:name="com.example.myapplication.Fragment2"
    android:label="fragment_2"
    tools:layout="@layout/fragment_2">

    <action
        android:id="@+id/action_2_to_1"
        app:destination="@id/fragment1"
        app:popUpTo="@+id/fragment1"/>
</fragment>
<fragment
    android:id="@+id/fragment1"
    android:name="com.example.myapplication.Fragment1"
    android:label="fragment_1"
    tools:layout="@layout/fragment_1">

        <argument
            android:name="someArgument"
            app:argType="string"
            app:nullable="false"
            android:defaultValue="Hello Word"/>
</fragment>

In your Fragment2 class, you call your action and pass your argument:

   val action = Fragment2Directions.action2To1("MY_STRING_ARGUMENT")
        findNavController().navigate(action)