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Spinner 在 Kotlin 中始终为 null

[英]Spinner is always null in Kotlin

 原文  2022-08-19 17:53:03  5   1    android/ android-studio/ kotlin/ spinner

问题描述

编辑：为了澄清事情，因为它们有点混乱，我的微调器在 signUpFragment class 中，这是 class 的片段，该片段位于名为 sign_up_login 的片段内的 viewPager 内，我将 viewcontent 设置为 sign_up_login从我的主要活动。 我在 signUpFragment.kt 中的微调器上收到错误，它是 country_list，上面写着“null object refrence”

我的 Spinner 在另一个片段内的 ViewPager 中的片段中，微调器的代码是：

class signupFragment : Fragment() {

val values: Array<String> = arrayOf("Test1", "Test2", "Test3")

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    val adapter = ArrayAdapter(requireContext(),
        android.R.layout.simple_spinner_item, values)
    country_list.adapter = adapter


   country_list.onItemSelectedListener = object : AdapterView.OnItemSelectedListener{
        override fun onItemSelected(p0: AdapterView<*>?, p1: View?, p2: Int, p3: Long) {
            Toast.makeText(requireContext(), "Selected "+ values[p2], Toast.LENGTH_SHORT).show()
        }

        override fun onNothingSelected(p0: AdapterView<*>?) {
        }

    }

}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_signup, container, false)
}

}

该片段位于框架布局中，该框架布局位于视图寻呼机中的片段内，该片段包含在另一个名为 fragment_sign_up_login 的片段中。 signUpFragment 的 XML 文件是：

<?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=".signupFragment">

<com.google.android.material.textfield.TextInputEditText
    android:id="@+id/lastNameInput"
    android:layout_width="150dp"
    android:layout_height="50dp"
    android:layout_marginTop="30dp"
    android:layout_marginEnd="56dp"
    android:hint="Last Name"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/passwordSignUp" />

<EditText
    android:id="@+id/email_signUp"
    android:layout_width="300dp"
    android:layout_height="50dp"
    android:layout_marginTop="10dp"
    android:ems="10"
    android:hint="Email"
    android:inputType="textEmailAddress"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<com.google.android.material.textfield.TextInputEditText
    android:id="@+id/firstNameInput"
    android:layout_width="150dp"
    android:layout_height="50dp"
    android:layout_marginTop="30dp"
    android:hint="First Name"
    app:layout_constraintEnd_toStartOf="@+id/lastNameInput"
    app:layout_constraintTop_toBottomOf="@+id/passwordSignUp" />

<EditText
    android:id="@+id/editTextNumber"
    android:layout_width="70dp"
    android:layout_height="48dp"
    android:layout_marginStart="54dp"
    android:layout_marginTop="30dp"
    android:ems="10"
    android:hint="Age"
    android:inputType="number"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/firstNameInput" />

<Spinner
    android:id="@+id/country_list"
    android:layout_width="200dp"
    android:layout_height="48dp"
    android:layout_marginTop="30dp"
    android:layout_marginEnd="56dp"
    android:background="@android:drawable/btn_dropdown"
    android:backgroundTint="@color/lightWhite"
    android:spinnerMode="dropdown"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/lastNameInput" />

<EditText
    android:id="@+id/passwordSignUp"
    android:layout_width="300dp"
    android:layout_height="50dp"
    android:layout_marginTop="30dp"
    android:layout_marginEnd="56dp"
    android:ems="10"
    android:hint="Password"
    android:inputType="textPassword"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/email_signUp" />

<Button
    android:id="@+id/signUpButton"
    android:layout_width="120dp"
    android:layout_height="50dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="40dp"
    android:backgroundTint="@color/white"
    android:text="Sign up"
    android:textAllCaps="false"
    android:textColor="@color/black"
    app:layout_constraintStart_toStartOf="@+id/country_list"
    app:layout_constraintTop_toBottomOf="@+id/country_list" />

  </androidx.constraintlayout.widget.ConstraintLayout>

我的主要活动是：

class MainActivity : AppCompatActivity() {


override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.fragment_sign_up_login)
    tabBarSL()
}

override fun onCreateView(name: String, context: Context, attrs: AttributeSet): View? {
    return super.onCreateView(name, context, attrs)
}

fun replaceFragment(fragment: Fragment){
    val fragmentManager = supportFragmentManager.beginTransaction()
    fragmentManager.replace(R.id.frameLayout, fragment).commit()
}


fun tabBarSL(){
    viewPagerSL.adapter = TPA(this,tabLayoutSL.tabCount)
    viewPagerSL.registerOnPageChangeCallback(object: ViewPager2.OnPageChangeCallback(){
        override fun onPageSelected(position: Int) {
            tabLayoutSL.selectTab(tabLayoutSL.getTabAt(position))
        }
    })

tabLayoutSL.addOnTabSelectedListener(object: TabLayout.OnTabSelectedListener{
    override fun onTabSelected(tab: TabLayout.Tab) {
        viewPagerSL.currentItem = tab.position
    }

    override fun onTabUnselected(tab: TabLayout.Tab?) {
    }

    override fun onTabReselected(tab: TabLayout.Tab?) {
    }

})
}

}

signUpLogin 片段的 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=".SignUpLoginFragment"
android:background="@drawable/backgroundsl">

<FrameLayout
    android:id="@+id/frameLayoutSignLogin"
    android:layout_width="match_parent"
    android:layout_height="450dp"
    android:layout_marginTop="205dp"
    app:layout_constraintTop_toTopOf="parent"
    tools:layout_editor_absoluteX="-45dp">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/viewPagerSL"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</FrameLayout>

<com.google.android.material.tabs.TabLayout
    android:id="@+id/tabLayoutSL"
    android:layout_width="236dp"
    android:layout_height="46dp"
    android:layout_marginTop="124dp"
    android:layout_marginEnd="88dp"
    android:background="@color/transparent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toTopOf="parent">

    <com.google.android.material.tabs.TabItem
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Sign up"
        />

    <com.google.android.material.tabs.TabItem
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Log in" />

</com.google.android.material.tabs.TabLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

我在我的微调器 country_list 上不断收到错误null object 参考，这是完整的错误 output ：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.viegera, PID: 10039
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference
    at com.example.viegera.signupFragment.onCreate(signupFragment.kt:33)
    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:2100)
    at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1971)
    at androidx.fragment.app.BackStackRecord.commitNow(BackStackRecord.java:305)
    at androidx.viewpager2.adapter.FragmentStateAdapter.placeFragmentInViewHolder(FragmentStateAdapter.java:341)
    at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:276)
    at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:67)
    at androidx.recyclerview.widget.RecyclerView.dispatchChildAttached(RecyclerView.java:7556)
    at androidx.recyclerview.widget.RecyclerView$5.addView(RecyclerView.java:860)
    at androidx.recyclerview.widget.ChildHelper.addView(ChildHelper.java:107)
    at androidx.recyclerview.widget.RecyclerView$LayoutManager.addViewInt(RecyclerView.java:8601)
    at androidx.recyclerview.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:8559)
    at androidx.recyclerview.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:8547)
    at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1641)
    at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
    at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3851)
    at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
    at android.view.View.layout(View.java:23717)
    at android.view.ViewGroup.layout(ViewGroup.java:6413)
    at androidx.viewpager2.widget.ViewPager2.onLayout(ViewPager2.java:527)
    at android.view.View.layout(View.java:23717)
    at android.view.ViewGroup.layout(ViewGroup.java:6413)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
    at android.view.View.layout(View.java:23717)
    at android.view.ViewGroup.layout(ViewGroup.java:6413)
    at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1873)
    at android.view.View.layout(View.java:23717)
    at android.view.ViewGroup.layout(ViewGroup.java:6413)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
    at android.view.View.layout(View.java:23717)
    at android.view.ViewGroup.layout(ViewGroup.java:6413)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
    at android.view.View.layout(View.java:23717)
    at android.view.ViewGroup.layout(ViewGroup.java:6413)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
    at android.view.View.layout(View.java:23717)
    at android.view.ViewGroup.layout(ViewGroup.java:6413)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
    at android.view.View.layout(View.java:23717)
    E/AndroidRuntime:     at android.view.ViewGroup.layout(ViewGroup.java:6413)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
    at com.android.internal.policy.DecorView.onLayout(DecorView.java:797)
    at android.view.View.layout(View.java:23717)
    at android.view.ViewGroup.layout(ViewGroup.java:6413)
    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3892)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:3282)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:2278)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8933)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1230)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1238)
    at android.view.Choreographer.doCallbacks(Choreographer.java:898)
    at android.view.Choreographer.doFrame(Choreographer.java:831)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1213)
    at android.os.Handler.handleCallback(Handler.java:942)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loopOnce(Looper.java:201)
    at android.os.Looper.loop(Looper.java:288)
    at android.app.ActivityThread.main(ActivityThread.java:7892)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)

1 个解决方案

解决方案1
 1 已采纳  2022-08-19 18:08:03

微调器是 null，因为微调器本身没有初始化。 Spinner 仅在创建片段视图时才会被初始化。 当它是 null 时，您正在尝试访问微调器。

您需要将此代码从onCreate移动到onViewCreated或onCreateView 。 因为只有在调用onCreateView时才会创建视图。 onCreate在onCreateView之前调用。 您可以在此处查看以了解有关片段生命周期的更多信息。

此外，不推荐使用 Kotlin 合成，因为 Android kotlin 扩展 Z8ED1A771BC236C2877AD93C699 插件已弃用。 所以建议迁移到viewBinding

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

    val adapter = ArrayAdapter(requireContext(),
        android.R.layout.simple_spinner_item, values)
    country_list.adapter = adapter


   country_list.onItemSelectedListener = object : AdapterView.OnItemSelectedListener{
        override fun onItemSelected(p0: AdapterView<*>?, p1: View?, p2: Int, p3: Long) {
            Toast.makeText(requireContext(), "Selected "+ values[p2], Toast.LENGTH_SHORT).show()
        }

        override fun onNothingSelected(p0: AdapterView<*>?) {
        }

    }
}

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