Conditional Fragment Code Example

You’ll conditionally navigate to a different fragment based upon whether the player answers all of the questions correctly or not.
1. Add the GameWonFragment and GameOverFragment to the navigation graph.
Create actions connecting the GameFragment to the GameWonFragment and GameOverFragment. Move to the GameFragment Kotlin file.
2. Navigate from the gameFragment to the gameWonFragment under the “We’ve won!” comment
Under the “We’ve won!” comment, find the nav controller from the view, and then navigate to the action. To do this, call view.findNavController().navigate( R.id.action_gameFragment_to_gameWonFragment).
// We've won!  Navigate to the gameWonFragment.
view.findNavController()
   .navigate(R.id.action_gameFragment_to_gameWonFragment)
3. Navigate from the gameFragment to the gameOverFragment under the “GameOver” comment
Under the “GameOver” comment, call
view.findNavController().navigate(R.id.action_gameFragment_to_gameOverFragment)
// Game over! A wrong answer sends us to the gameOverFragment.
view.findNavController().
   navigate(R.id.action_gameFragment_to_gameOverFragment)
Now the game is more functionalCode:

package com.example.android.navigation

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.appcompat.app.AppCompatActivity
import androidx.databinding.DataBindingUtil
import androidx.fragment.app.Fragment
import androidx.navigation.NavDirections
import androidx.navigation.findNavController
import com.example.android.navigation.databinding.FragmentGameBinding

class GameFragment : Fragment() {
    data class Question(
            val text: String,
            val answers: List<String>)

    // The first answer is the correct one.  We randomize the answers before showing the text.
    // All questions must have four answers.  We'd want these to contain references to string
    // resources so we could internationalize. (or better yet, not define the questions in code...)
    private val questions: MutableList<Question> = mutableListOf(
            Question(text = "What is Android Jetpack?",
                    answers = listOf("all of these", "tools", "documentation", "libraries")),
            Question(text = "Base class for Layout?",
                    answers = listOf("ViewGroup", "ViewSet", "ViewCollection", "ViewRoot")),
            Question(text = "Layout for complex Screens?",
                    answers = listOf("ConstraintLayout", "GridLayout", "LinearLayout", "FrameLayout")),
            Question(text = "Pushing structured data into a Layout?",
                    answers = listOf("Data Binding", "Data Pushing", "Set Text", "OnClick")),
            Question(text = "Inflate layout in fragments?",
                    answers = listOf("onCreateView", "onViewCreated", "onCreateLayout", "onInflateLayout")),
            Question(text = "Build system for Android?",
                    answers = listOf("Gradle", "Graddle", "Grodle", "Groyle")),
            Question(text = "Android vector format?",
                    answers = listOf("VectorDrawable", "AndroidVectorDrawable", "DrawableVector", "AndroidVector")),
            Question(text = "Android Navigation Component?",
                    answers = listOf("NavController", "NavCentral", "NavMaster", "NavSwitcher")),
            Question(text = "Registers app with launcher?",
                    answers = listOf("intent-filter", "app-registry", "launcher-registry", "app-launcher")),
            Question(text = "Mark a layout for Data Binding?",
                    answers = listOf("<layout>", "<binding>", "<data-binding>", "<dbinding>"))
    )

    lateinit var currentQuestion: Question
    lateinit var answers: MutableList<String>
    private var questionIndex = 0
    private val numQuestions = Math.min((questions.size + 1) / 2, 3)

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {

        // Inflate the layout for this fragment
        val binding = DataBindingUtil.inflate<FragmentGameBinding>(
                inflater, R.layout.fragment_game, container, false)

        // Shuffles the questions and sets the question index to the first question.
        randomizeQuestions()

        // Bind this fragment class to the layout
        binding.game = this

        // Set the onClickListener for the submitButton
        binding.submitButton.setOnClickListener @Suppress("UNUSED_ANONYMOUS_PARAMETER")
        { view: View ->
            val checkedId = binding.questionRadioGroup.checkedRadioButtonId
            // Do nothing if nothing is checked (id == -1)
            if (-1 != checkedId) {
                var answerIndex = 0
                when (checkedId) {
                    R.id.secondAnswerRadioButton -> answerIndex = 1
                    R.id.thirdAnswerRadioButton -> answerIndex = 2
                    R.id.fourthAnswerRadioButton -> answerIndex = 3
                }
                // The first answer in the original question is always the correct one, so if our
                // answer matches, we have the correct answer.
                if (answers[answerIndex] == currentQuestion.answers[0]) {
                    questionIndex++
                    // Advance to the next question
                    if (questionIndex < numQuestions) {
                        currentQuestion = questions[questionIndex]
                        setQuestion()
                        binding.invalidateAll()
                    } else {
                        // We've won!  Navigate to the gameWonFragment.
                        view.findNavController().navigate(R.id.action_gameFragment_to_gameWonFragment)
                    }
                } else {
                    // Game over! A wrong answer sends us to the gameOverFragment.
                    view.findNavController().navigate(R.id.action_gameFragment_to_gameOverFragment)
                }
            }
        }
        return binding.root
    }

    // randomize the questions and set the first question
    private fun randomizeQuestions() {
        questions.shuffle()
        questionIndex = 0
        setQuestion()
    }

    // Sets the question and randomizes the answers.  This only changes the data, not the UI.
    // Calling invalidateAll on the FragmentGameBinding updates the data.
    private fun setQuestion() {
        currentQuestion = questions[questionIndex]
        // randomize the answers into a copy of the array
        answers = currentQuestion.answers.toMutableList()
        // and shuffle them
        answers.shuffle()
        (activity as AppCompatActivity).supportActionBar?.title = getString(R.string.title_android_trivia_question, questionIndex + 1, numQuestions)
    }
}