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。
