FragmentContainerView中的问题与解决方法

作者: 普通路人 | 来源:发表于2021-12-08 15:08 被阅读0次

FragmentContainerView中的问题与解决方法

一、发现问题

1、错误表现

今天在做一个项目的时候，发现了一个莫名奇妙的问题。根据官方的建议，使用FragmentContainerView去切换和处理Fragment。

为布局文件中的FragmentContainerView设置一个开始Fragment，我称之为FragmentA，同时需要FragmentA传入参数进行初始化，然后问题出现了：编译通过,布局文件没有任何问题，运行时报错并退出应用，报错指出我的布局文件出问题，同时提示一个用到的参数为空。

当场裂开，此外我注意到此前我的代码中FragmentA会被初始化两次，我注释掉那个提示为空的参数，一切豁然开朗。

原来FragmentA被初始化了两次：第一次初始化是在setContentView的时候进行初始化，此时没有参数传入，导致参数为空，导致android.view.InflateException错误，再导致提示布局文件错误。

我想尝试复现这个错误，并尝试解决这个问题。

2、错误日志

--------- beginning of crash
2021-12-07 20:07:43.034 10842-10842/ink.ptlr.nodemusic E/AndroidRuntime: FATAL EXCEPTION: main
    Process: ink.ptlr.nodemusic, PID: 10842
    java.lang.RuntimeException: Unable to start activity ComponentInfo{ink.ptlr.nodemusic/ink.ptlr.nodemusic.activity.UtilsActivity}: android.view.InflateException: Binary XML file line #18 in ink.ptlr.nodemusic:layout/activity_utils: Binary XML file line #18 in ink.ptlr.nodemusic:layout/activity_utils: Error inflating class androidx.fragment.app.FragmentContainerView
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4060)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4247)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2613)
        at android.os.Handler.dispatchMessage(Handler.java:110)
        at android.os.Looper.loop(Looper.java:219)
        at android.app.ActivityThread.main(ActivityThread.java:8668)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1109)
     Caused by: android.view.InflateException: Binary XML file line #18 in ink.ptlr.nodemusic:layout/activity_utils: Binary XML file line #18 in ink.ptlr.nodemusic:layout/activity_utils: Error inflating class androidx.fragment.app.FragmentContainerView
     Caused by: android.view.InflateException: Binary XML file line #18 in ink.ptlr.nodemusic:layout/activity_utils: Error inflating class androidx.fragment.app.FragmentContainerView
     Caused by: java.lang.NullPointerException
        at ink.ptlr.nodemusic.fragment.MusicListFragment.onCreate(MusicListFragment.kt:46)
        at androidx.fragment.app.Fragment.performCreate(Fragment.java:2949)
        at androidx.fragment.app.FragmentStateManager.create(FragmentStateManager.java:475)
        at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:278)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2106)
        at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1971)
        at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:311)
        at androidx.fragment.app.FragmentContainerView.<init>(FragmentContainerView.java:180)
        at androidx.fragment.app.FragmentLayoutInflaterFactory.onCreateView(FragmentLayoutInflaterFactory.java:52)
        at androidx.fragment.app.FragmentController.onCreateView(FragmentController.java:135)
        at androidx.fragment.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:319)
        at androidx.fragment.app.FragmentActivity.onCreateView(FragmentActivity.java:298)
        at android.view.LayoutInflater.tryCreateView(LayoutInflater.java:1079)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:1007)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:971)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:1133)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:1094)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:692)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:536)
        at com.android.internal.policy.HwPhoneLayoutInflater.inflate(HwPhoneLayoutInflater.java:138)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:483)
        at androidx.appcompat.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:699)
        at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:195)
        at ink.ptlr.nodemusic.activity.UtilsActivity.onCreate(UtilsActivity.kt:25)
        at android.app.Activity.performCreate(Activity.java:8214)
        at android.app.Activity.performCreate(Activity.java:8202)
2021-12-07 20:07:43.034 10842-10842/ink.ptlr.nodemusic E/AndroidRuntime:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1320)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4033)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4247)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2613)
        at android.os.Handler.dispatchMessage(Handler.java:110)
        at android.os.Looper.loop(Looper.java:219)
        at android.app.ActivityThread.main(ActivityThread.java:8668)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1109)
2021-12-07 20:07:43.041 10842-10842/ink.ptlr.nodemusic I/Process: Sending signal. PID: 10842 SIG: 9

二、问题复现

1、创建项目

新建一个名为FCVT(FragmentContainerViewTest)的项目,在下面新建一个MainActivity和一个TestFragment，采用FragmentContainerView。
结构如下：

TCVT项目结构
【提示】需要以下依赖：

implementation 'androidx.fragment:fragment:1.3.2'

MainActivity

负责载入布局文件并初始化Fragment。

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <!-- 动态加载Fragment -->
    <!-- 并设置起始Fragment为TestFragment -->
    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/fragmentContainerView"
        android:name="ink.ptlr.fcvt.TestFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:layout="@layout/test_fragment" />
<!-- 报错会指向上一行，但实际上这个布局文件没有任何问题 -->
</androidx.constraintlayout.widget.ConstraintLayout>

MainActyvity.kt

package ink.ptlr.fcvt

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        /* 在这里被实例化一次
         * 此时，没有传入数据参数，为空，会导致报错
         */
        setContentView(R.layout.activity_main)
        val transaction = supportFragmentManager.beginTransaction()
        for(fragment in supportFragmentManager.fragments){
            transaction.remove(fragment)
        }
        // 第二次被初始化，可正常执行
        val fcvt: TestFragment = TestFragment.newInstance("Hello FCVT",1024)
        transaction.add(fcvt,"FCVT")
        transaction.commitNow()
    }
}

TestFragment

test_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".TestFragment">
    <!-- 用于显示信息 -->
    <TextView
        android:id="@+id/tvMsg"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:textAlignment="center"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

TestFragment.kt

package ink.ptlr.fcvt

import android.annotation.SuppressLint
import androidx.lifecycle.ViewModelProvider
import android.os.Bundle
import android.util.Log
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView

private const val KEY_MSG = "MSG"
private const val KEY_NUM = "NUM"
// private var count = 1
class TestFragment : Fragment() {
    companion object {
        /*这里传入参数*/
        fun newInstance(msg: String, num: Int) = TestFragment().apply {
            arguments = Bundle().apply {
                putString(KEY_MSG,msg)
                putInt(KEY_NUM, num)
            }
        }
    }
    private lateinit var viewModel: TestViewModel
    private var msg: String? = null
    private var num: Int? = null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        /*获取参数*/
        arguments?.let {
            msg = it.getString(KEY_MSG)
            num = it.getInt(KEY_NUM)
        }
        /*此时不能使用参数num,否则会报错*/
        var result = num!!.plus(1)
        Log.i("FCVT","MSG: $msg, NUM: ${num}")
        //count++
    }
    @SuppressLint("SetTextI18n")
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val rootView:View = inflater.inflate(R.layout.test_fragment, container, false)
        val tvMsg: TextView = rootView.findViewById(R.id.tvMsg)
        tvMsg.text = "MSG: $msg, NUM: $num"
        return rootView
    }
    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        viewModel = ViewModelProvider(this).get(TestViewModel::class.java)
        // TODO: Use the ViewModel
    }
}

2、编译运行于报错

上面的代码可以通过编译，但运行时应用闪退，报错日志如下：

 --------- beginning of crash
2021-12-08 12:48:10.344 31676-31676/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: ink.ptlr.fcvt, PID: 31676
    java.lang.RuntimeException: Unable to start activity ComponentInfo{ink.ptlr.fcvt/ink.ptlr.fcvt.MainActivity}: android.view.InflateException: Binary XML file line #19 in ink.ptlr.fcvt:layout/activity_main: Binary XML file line #19 in ink.ptlr.fcvt:layout/activity_main: Error inflating class androidx.fragment.app.FragmentContainerView
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4060)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4247)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2613)
        at android.os.Handler.dispatchMessage(Handler.java:110)
        at android.os.Looper.loop(Looper.java:219)
        at android.app.ActivityThread.main(ActivityThread.java:8668)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1109)
     Caused by: android.view.InflateException: Binary XML file line #19 in ink.ptlr.fcvt:layout/activity_main: Binary XML file line #19 in ink.ptlr.fcvt:layout/activity_main: Error inflating class androidx.fragment.app.FragmentContainerView
     Caused by: android.view.InflateException: Binary XML file line #19 in ink.ptlr.fcvt:layout/activity_main: Error inflating class androidx.fragment.app.FragmentContainerView
     Caused by: java.lang.NullPointerException
        at ink.ptlr.fcvt.TestFragment.onCreate(TestFragment.kt:39)
        at androidx.fragment.app.Fragment.performCreate(Fragment.java:2949)
        at androidx.fragment.app.FragmentStateManager.create(FragmentStateManager.java:475)
        at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:278)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2106)
        at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1971)
        at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:311)
        at androidx.fragment.app.FragmentContainerView.<init>(FragmentContainerView.java:176)
        at androidx.fragment.app.FragmentLayoutInflaterFactory.onCreateView(FragmentLayoutInflaterFactory.java:52)
        at androidx.fragment.app.FragmentController.onCreateView(FragmentController.java:135)
        at androidx.fragment.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:319)
        at androidx.fragment.app.FragmentActivity.onCreateView(FragmentActivity.java:298)
        at android.view.LayoutInflater.tryCreateView(LayoutInflater.java:1079)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:1007)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:971)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:1133)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:1094)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:692)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:536)
        at com.android.internal.policy.HwPhoneLayoutInflater.inflate(HwPhoneLayoutInflater.java:138)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:483)
        at androidx.appcompat.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:696)
        at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:170)
        at ink.ptlr.fcvt.MainActivity.onCreate(MainActivity.kt:12)
        at android.app.Activity.performCreate(Activity.java:8214)
        at android.app.Activity.performCreate(Activity.java:8202)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1320)
2021-12-08 12:48:10.344 31676-31676/? E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4033)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4247)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2613)
        at android.os.Handler.dispatchMessage(Handler.java:110)
        at android.os.Looper.loop(Looper.java:219)
        at android.app.ActivityThread.main(ActivityThread.java:8668)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1109)

三、错误分析

这个问题困扰了我佷久，因为出现了不止一次，而且每次都困扰了我很久。
仔细分析后发现了问题所在：
在setContentView时TestFragment会被实例化，此时需要自定义的参数是没有初始化的，不能使用。
在代码中:

/*此时不能使用参数num,否则会报错*/
var result = num!!.plus(1)

我使用!!告诉编译器这个数据不为空，于是编译通过，但实际情况是这个数据会出现为空的情况，于是在运行的时候出现了错误。
错误的原因：在上述项目中，TesTFragment会被初始化两次，第一次是setContentView的时候，第二次是调用TestFragment.instance(msg: String, num: Int)的时候。

四、解决方法

思路：在创建时传入参数或只实例化一次
需求不能变，在初始化时传入参数是要求，在仔细阅读官方文档Fragment 管理器 | Android 开发者 | Android Developers (google.cn)后，通过自定义FragmentFactory解决问题（创建时传入参数）。
修改后:
TestFragment.kt

package ink.ptlr.fcvt

import android.annotation.SuppressLint
import androidx.lifecycle.ViewModelProvider
import android.os.Bundle
import android.util.Log
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.fragment.app.FragmentFactory

private const val KEY_MSG = "MSG"
private const val KEY_NUM = "NUM"
// private var count = 1
class TestFragment() : Fragment() {
    companion object {
        /*这里传入参数*/
        fun newInstance(msg: String, num: Int) = TestFragment().apply {
            arguments = Bundle().apply {
                putString(KEY_MSG,msg)
                putInt(KEY_NUM, num)
            }
        }
    }
    private lateinit var viewModel: TestViewModel
    private var msg: String? = null
    private var num: Int? = null
    init {
        msg = "Init By default"
    }
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        /*获取参数*/
        arguments?.let {
            msg = it.getString(KEY_MSG)
            num = it.getInt(KEY_NUM)
        }
        /*此时不能使用参数num,否则会报错*/
        //var result = num!!.plus(1)
        Log.i("FCVT","MSG: $msg, NUM: ${num}")
        //count++
    }
    @SuppressLint("SetTextI18n")
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        Log.i("FCVT","OCV")
        var rootView:View = inflater.inflate(R.layout.test_fragment, container, false)
        val tvMsg: TextView = rootView.findViewById(R.id.tvMsg)
        tvMsg.text = "MSG: $msg, NUM: $num"
        return rootView
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        viewModel = ViewModelProvider(this).get(TestViewModel::class.java)
        // TODO: Use the ViewModel
    }
    // 自定义的FragmentFactory，内部类
    class MyFactory(var msg: String, var num: Int): FragmentFactory(){
        override fun instantiate(classLoader: ClassLoader, className: String): Fragment =
            when(loadFragmentClass(classLoader, className)){
                TestFragment::class.java -> newInstance(msg, num)
                else -> super.instantiate(classLoader, className)
            }

    }
}

MainActivity.kt

package ink.ptlr.fcvt

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        // 使用自定义的FragmentFactory,必须在super.onCreate()之前
        supportFragmentManager.fragmentFactory = TestFragment.MyFactory("HELLO FCVT",1024)
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

五、总结

这个问题是我偷懒，鬼官方太过信任，使用官方模板和不熟悉安卓开发导致的，此外，此处还有一个添加Fragment时会出现空白的问题，今后需要解决。
PS: 发现并解决这个问题内心十分喜悦，希望能把这种喜悦分享给大家，并对大家有一定帮助。

FragmentContainerView中的问题与解决方法

FragmentContainerView中的问题与解决方法

一、发现问题

1、错误表现

2、错误日志

二、问题复现

1、创建项目

MainActivity

TestFragment

2、编译运行于报错

三、错误分析

四、解决方法

五、总结

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