ViewPager加载ViewNotesFragment失败，提示找不到视图ID求助

致命异常信息 #

FATAL EXCEPTION: main
Process: io.lionpswn.kodular.notepad, PID: 24071
java.lang.IllegalArgumentException: No view found for id 0x7f08021a (io.lionpswn.kodular.notepad:id/viewPager) for fragment ViewToDo{df73341} (911e855d-2d18-427e-b76e-f31ad6ae5083 id=0x7f08021a tag=android:switcher:2131231258:1)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:547)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:272)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1943)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1839)
at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1751)
at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:323)
at androidx.fragment.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:249)
at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1244)
at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1092)
at androidx.viewpager.widget.ViewPager.onMeasure(ViewPager.java:1622)
at android.view.View.measure(View.java:26010)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7105)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:760)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:833)
at android.view.View.measure(View.java:26010)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7105)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:145)
at android.view.View.measure(View.java:26010)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7105)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
at android.view.View.measure(View.java:26010)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7105)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:26010)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7105)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
at android.view.View.measure(View.java:26010)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:7105)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:767)
at android.view.View.measure(View.java:26010)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:3629)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:2407)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2673)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:2129)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8625)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1034)
at android.view.Choreographer.doCallbacks(Choreographer.java:858)
at android.view.Choreographer.doFrame(Choreographer.java:789)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1019)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:236)
at android.app.ActivityThread.main(ActivityThread.java:7912)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:620)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1011)

问题描述 #

使用ViewPager加载ViewNotesFragment时，运行时无法正确填充布局，抛出上述异常。其他空白Fragment可正常加载，但ViewNotesFragment不行，布局文件本身无误，却提示找不到视图ID。

相关代码 #

ViewPagerAdapter #

package io.lionpswn.kodular.notepad

import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentManager
import androidx.fragment.app.FragmentPagerAdapter
import androidx.viewpager.widget.PagerAdapter
import io.lionpswn.kodular.notepad.presenter.viewNotes.ViewNotes

class PagerAdapter(val fm: FragmentManager) :
FragmentPagerAdapter(fm) {
override fun getItem(position: Int): Fragment{

        return when(position){
            0 -> addToDo()
            1 -> ViewToDo()
            else -> ViewToDo()
        }
    }
    
    override fun getCount(): Int {
        return 2
    }
    
    override fun getPageTitle(position: Int): CharSequence? {
        return when(position){
            0 -> "ViewNotes()1"
            1 -> "ViewToDo()2"
            else -> "ViewToDo()3"
        }
    }

}

ViewNotes Fragment #

package io.lionpswn.kodular.notepad.presenter.viewNotes

import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.databinding.DataBindingUtil
import androidx.fragment.app.Fragment
import androidx.fragment.app.viewModels
import androidx.recyclerview.widget.LinearLayoutManager
import dagger.hilt.android.AndroidEntryPoint
import io.lionpswn.kodular.notepad.R
import io.lionpswn.kodular.notepad.databinding.FragmentViewnotesBinding
import io.lionpswn.kodular.notepad.domain.model.Note

@AndroidEntryPoint
class ViewNotes : Fragment() {
var isAdNotShown:Boolean=true
val viewModel: ViewNotesViewModel by viewModels()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val binding: FragmentViewnotesBinding =DataBindingUtil.setContentView(this.requireActivity(), R.layout.fragment_viewnotes)
var context=this
val recyclerView=binding.recyclerview
var list:List<Note> = mutableListOf()
viewModel.onEvent(event.loadAd(this.requireContext(), binding.adView))
var adapter = RecyclerViewAdapter(list)
recyclerView.setHasFixedSize(true)
recyclerView.adapter = adapter
recyclerView.layoutManager = LinearLayoutManager(this.requireContext())

        viewModel.list.observe(viewLifecycleOwner,{
            Log.d("check",it.toString())
            list=it
            var adapter = RecyclerViewAdapter(list)
            recyclerView.adapter = adapter
            adapter.notifyDataSetChanged()
        })
    
        binding.fab.setOnClickListener {
            viewModel.onEvent(event.newNoteFab(this.requireContext()))
        }
        return binding.root

}}

解决方案 #

核心问题 #

ViewNotes的onCreateView中错误使用了DataBindingUtil.setContentView，这个方法是用来给Activity设置整个内容视图的，调用它会把Fragment的布局直接替换掉Activity原本包含ViewPager的布局，导致FragmentManager找不到ViewPager的ID，从而抛出异常。

修复代码 #

将ViewNotes中布局绑定的代码替换为DataBindingUtil.inflate，这是Fragment中正确的布局填充方式：

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    // 替换原来的setContentView为inflate
    val binding: FragmentViewnotesBinding = DataBindingUtil.inflate(
        inflater,
        R.layout.fragment_viewnotes,
        container,
        false // 不要直接附加到container，ViewPager会负责添加
    )
    // 剩余代码保持不变
    val recyclerView=binding.recyclerview
    var list:List<Note> = mutableListOf()
    viewModel.onEvent(event.loadAd(this.requireContext(), binding.adView))
    var adapter = RecyclerViewAdapter(list)
    recyclerView.setHasFixedSize(true)
    recyclerView.adapter = adapter
    recyclerView.layoutManager = LinearLayoutManager(this.requireContext())

    viewModel.list.observe(viewLifecycleOwner,{
        Log.d("check",it.toString())
        list=it
        var adapter = RecyclerViewAdapter(list)
        recyclerView.adapter = adapter
        adapter.notifyDataSetChanged()
    })

    binding.fab.setOnClickListener {
        viewModel.onEvent(event.newNoteFab(this.requireContext()))
    }
    return binding.root
}

额外优化建议 #

• 数据更新时不需要每次创建新的RecyclerViewAdapter，可以在Adapter中添加更新数据的方法，避免不必要的对象创建：

// 在RecyclerViewAdapter中添加方法
fun updateData(newList: List<Note>) {
    this.list = newList
    notifyDataSetChanged()
}

// 在Fragment的观察者中调用
viewModel.list.observe(viewLifecycleOwner,{
    Log.d("check",it.toString())
    adapter.updateData(it)
})

• var context=this可以直接用requireContext()代替，无需额外声明。

内容的提问来源于stack exchange，提问作者jiji solaman