Is there a method that works like start fragment for result?

Question

I currently have a fragment in an overlay. This is for signing in to the service. In the phone app, each of the steps I want to show in the overlay are their own screens and

Answer 1

We can simply share the same ViewModel between fragments

SharedViewModel

import android.arch.lifecycle.MutableLiveData
import android.arch.lifecycle.ViewModel

class SharedViewModel : ViewModel() {

    val stringData: MutableLiveData<String> by lazy {
        MutableLiveData<String>()
    }

}

FirstFragment

import android.arch.lifecycle.Observer
import android.os.Bundle
import android.arch.lifecycle.ViewModelProviders
import android.support.v4.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup

class FirstFragment : Fragment() {

    private lateinit var sharedViewModel: SharedViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        activity?.run {
            sharedViewModel = ViewModelProviders.of(activity).get(SharedViewModel::class.java)
        }
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment_first, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        sharedViewModel.stringData.observe(this, Observer { dateString ->
            // get the changed String
        })

    }

}

SecondFragment

import android.arch.lifecycle.ViewModelProviders
import android.os.Bundle
import android.support.v4.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGrou

class SecondFragment : Fragment() {

    private lateinit var sharedViewModel: SharedViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        activity?.run {
            sharedViewModel = ViewModelProviders.of(activity).get(SharedViewModel::class.java)
        }
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment_first, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        changeString()
    }

    private fun changeString() {
        sharedViewModel.stringData.value = "Test"
    }

}

Answer 2

A solution using interfaces (and Kotlin). The core idea is to define a callback interface, implement it in your activity, then call it from your fragment.

First, create an interface ActionHandler:

interface ActionHandler {
    fun handleAction(actionCode: String, result: Int)
}

Next, call this from your child (in this case, your fragment):

companion object {
    const val FRAGMENT_A_CLOSED = "com.example.fragment_a_closed"
}

fun closeFragment() {
    try {
        (activity as ActionHandler).handleAction(FRAGMENT_A_CLOSED, 1234)
    } catch (e: ClassCastException) {
        Timber.e("Calling activity can't get callback!")
    }
    dismiss()
}

Finally, implement this in your parent to receive the callback (in this case, your Activity):

class MainActivity: ActionHandler { 
    override fun handleAction(actionCode: String, result: Int) {
        when {
            actionCode == FragmentA.FRAGMENT_A_CLOSED -> {
                doSomething(result)
            }
            actionCode == FragmentB.FRAGMENT_B_CLOSED -> {
                doSomethingElse(result)
            }
            actionCode == FragmentC.FRAGMENT_C_CLOSED -> {
                doAnotherThing(result)
            }
        }
    }

Answer 3

My 2 cents.

I switch beween fragments by swapping an old fragment with a new one using hide and show/add (existing/new). So this answer is for devs who use fragments like I do.

Then I use the onHiddenChanged method to know that the old fragment got switched to back from the new one. See code below.

Before leaving the new fragment, I set a result in a global parameter to be queried by the old fragment. This is a very naive solution.

@Override
public void onHiddenChanged(boolean hidden) {
    super.onHiddenChanged(hidden);
    if (hidden) return;
    Result result = Result.getAndReset();
    if (result == Result.Refresh) {
        refresh();
    }
}

public enum Result {
    Refresh;

    private static Result RESULT;

    public static void set(Result result) {
        if (RESULT == Refresh) {
            // Refresh already requested - no point in setting anything else;
            return;
        }
        RESULT = result;
    }

    public static Result getAndReset() {
        Result result = RESULT;
        RESULT = null;
        return result;
    }
}

Answer 4

All of the Fragments live inside Activities. Starting a Fragment for a result doesn't make much sense, because the Activity that houses it always has access to it, and vice versa. If the Fragment needs to pass on a result, it can access its Activity and set its result and finish it. In the case of swapping Fragments in a single Activity, well the Activity is still accessible by both Fragments, and all your message passing can simply go through the Activity.

Just remember that you always have communication between a Fragment and its Activity. Starting for and finishing with a result is the mechanism for communication between Activities - The Activities can then delegate any necessary information to their Fragments.

Answer 5

Recently, Google has just added a new ability to FragmentManager which made the FragmentManager be able to act as a central store for fragment results. We can pass the data back and forth between Fragments easily.

Starting fragment.

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    // Use the Kotlin extension in the fragment-ktx artifact
    setResultListener("requestKey") { key, bundle ->
        // We use a String here, but any type that can be put in a Bundle is supported
        val result = bundle.getString("bundleKey")
        // Do something with the result...
    }
}

A Fragment that we want the result back.

button.setOnClickListener {
    val result = "result"
    // Use the Kotlin extension in the fragment-ktx artifact
    setResult("requestKey", bundleOf("bundleKey" to result))
}

The snippet is taken from Google's official documents. https://developer.android.com/training/basics/fragments/pass-data-between#kotlin

At the date of this answer written, this feature is still in alpha state. You can try it out using this dependency.

androidx.fragment:fragment:1.3.0-alpha05

Answer 6

There is an Android library - FlowR that allows you to start fragments for results.

Starting a fragment for result.

Flowr.open(RequestFragment.class)
    .displayFragmentForResults(getFragmentId(), REQUEST_CODE);

Handling results in the calling fragment.

@Override
protected void onFragmentResults(int requestCode, int resultCode, Bundle data) {
    super.onFragmentResults(requestCode, resultCode, data);

    if (requestCode == REQUEST_CODE) {
        if (resultCode == Activity.RESULT_OK) {
            demoTextView.setText("Result OK");
        } else {
            demoTextView.setText("Result CANCELED");
        }
    }
}

Setting the result in the Fragment.

Flowr.closeWithResults(getResultsResponse(resultCode, resultData));