Pass data/bundle using navigateUp in Android Navigation Component

问题

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 can I pass data to previous fragment? navigateUp() does not have any facility to pass data to previous fragment. Even I did not find solution using Safe Args. It's passing data forward. I want to have in backward Frad B -> Frag A.

My code to go back to previous fragment

Navigation.findNavController(view).navigateUp()

My question is, How can i get data in previous fragment. I can navigate to Frag A from Frag B using

回答1:

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:

Create view model which will keep the data:

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

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

Observe data changes in Fragment1:

class Fragment1 : Fragment() {

    private lateinit var viewModel: SharedViewModel

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

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 onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        viewModel = ViewModelProviders.of(activity!!).get(SharedViewModel::class.java)

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

I hope answer helps.