Fragment.requireArguments()崩溃了一个安卓应用程序

Question

我学习如何在Google代码库上制作android应用程序。现在我正在讨论这个问题(https://developer.android.com/codelabs/kotlin-android-training-start-external-activity#3)。

我完成了课程的任务。但是当我点击一个按钮导航到一个片段时，我的应用程序在android Studio的一个Android虚拟设备上崩溃了。

密码在这里。

/*
 * Copyright 2018, The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.navigation

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.databinding.DataBindingUtil
import androidx.fragment.app.Fragment
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, don't 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 = "What is the base class for layouts?",
                    answers = listOf("ViewGroup", "ViewSet", "ViewCollection", "ViewRoot")),
            Question(text = "What layout do you use for complex screens?",
                    answers = listOf("ConstraintLayout", "GridLayout", "LinearLayout", "FrameLayout")),
            Question(text = "What do you use to push structured data into a layout?",
                    answers = listOf("Data binding", "Data pushing", "Set text", "An OnClick method")),
            Question(text = "What method do you use to inflate layouts in fragments?",
                    answers = listOf("onCreateView()", "onActivityCreated()", "onCreateLayout()", "onInflateLayout()")),
            Question(text = "What's the build system for Android?",
                    answers = listOf("Gradle", "Graddle", "Grodle", "Groyle")),
            Question(text = "Which class do you use to create a vector drawable?",
                    answers = listOf("VectorDrawable", "AndroidVectorDrawable", "DrawableVector", "AndroidVector")),
            Question(text = "Which one of these is an Android navigation component?",
                    answers = listOf("NavController", "NavCentral", "NavMaster", "NavSwitcher")),
            Question(text = "Which XML element lets you register an activity with the launcher activity?",
                    answers = listOf("intent-filter", "app-registry", "launcher-registry", "app-launcher")),
            Question(text = "What do you use to 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(GameFragmentDirections.actionGameFragmentToGameWonFragment(numQuestions, questionIndex))
                    }
                } else {
                    // Game over! A wrong answer sends us to the gameOverFragment.
                    view.findNavController().navigate(GameFragmentDirections.actionGameFragmentToGameOverFragment())
                }
            }
        }

        val requireArgs = requireArguments()
        val args = GameWonFragmentArgs.fromBundle(requireArgs)
        Toast.makeText(context, "NumCorrect: ${args.numCorrect}, NumQuestions: ${args.numQuestions}", Toast.LENGTH_LONG).show()
        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)
    }
}

上述代码在此发生致命异常。

val requireArgs = requireArguments()

堆栈追踪在这里。

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.android.navigation, PID: 5761
    java.lang.IllegalStateException: Fragment GameFragment{11178cb} (b2ef6b6f-1bdd-4395-8590-7386740263fb) id=0x7f0800ff} does not have any arguments.
        at androidx.fragment.app.Fragment.requireArguments(Fragment.java:679)
        at com.example.android.navigation.GameFragment.onCreateView(GameFragment.kt:115)
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698)
        at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:320)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1187)
        at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2224)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1997)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1953)
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849)
        at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
        at android.os.Handler.handleCallback(Handler.java:789)
        at android.os.Handler.dispatchMessage(Handler.java:98)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6541)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

我搜索过Stackoverflow或Google，但我没有找到。

Answer 1

与您的GameWonFragment不同，GameFragment从未被分配过任何参数。

没有参数的片段将导致requireArguments()在访问时崩溃。