我对片段中的 spinneradapter 有问题

Question

我正在使用 kotlin 开发 android 应用程序。我使用 AddDebtFragment 中的 3 个微调器和资源文件中的 3 个字符串数组设置了选定值。但是当我尝试从我的 HomeFragment 导航到这个片段时，应用程序被终止并且它在片段 Logcat 上显示问题

这是我在 fragment_add_debt.xml

中的微调器

<Spinner
    android:id="@+id/debtCategorySpinner"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    style="@style/SpinnerStyle"
    android:spinnerMode="dialog" 
    android:entries="@array/debtCategoryList"/>

<Spinner
    android:id="@+id/financialNameSpinner"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:spinnerMode="dialog"
    style="@style/SpinnerStyle"
    android:entries="@array/financialNameList"/>
<Spinner
        android:id="@+id/rateTypeSpinner"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        style="@style/SpinnerStyle"
        android:spinnerMode="dialog"
        android:entries="@array/rateTypeList"/>

资源文件中的字符串数组

<string-array name="financialNameList">
        <item>Bangkok Bank</item>
        <item>Kasikorn Bank</item>
        <item>Krung Thai Bank</item>
        <item>The Siam Commercial Bank</item>
        <item>TMB Bank</item>
        <item>Bank of Ayudhya</item>
    </string-array>

    <string-array name="debtCategoryList">
        <item>Personal Loan</item>
        <item>Vehicle Loan</item>
        <item>Indonesia</item>
        <item>Mortgage</item>
        <item>Student Loan</item>
        <item>Credit Card</item>
    </string-array>

    <string-array name="rateTypeList">
        <item>Effective Rate</item>
        <item>Flat Rate</item>
        <item>Fixed Rate</item>
        <item>MRR</item>
        <item>MOR</item>
        <item>MLR</item>
        <item>Student Rate</item>
        <item>Credit Card</item>
        <item>Ceiling</item>
        <item>Default</item>
    </string-array>

AddDebtFragment

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.AdapterView
import android.widget.ArrayAdapter
import com.example.debtrearragement.R
import kotlinx.android.synthetic.main.fragment_add_debt.*
class AddDebtFragment : Fragment(), AdapterView.OnItemSelectedListener {

    private val financialSpinner = financialNameSpinner
    private val debtSpinner = debtCategorySpinner
    private val rateSpinner = rateTypeSpinner

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.fragment_add_debt, container, false)
    }

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

        ArrayAdapter.createFromResource(context, R.array.financialNameList, android.R.layout.simple_spinner_item)
            .also { adapter ->
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item)
            financialSpinner.adapter
            financialSpinner.onItemSelectedListener
        }

        ArrayAdapter.createFromResource(this.context, R.array.debtCategoryList, android.R.layout.simple_spinner_dropdown_item)
            .also { adapter ->
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item)
            debtSpinner.adapter
            debtSpinner.onItemSelectedListener
        }

        ArrayAdapter.createFromResource(this.context, R.array.rateTypeList, android.R.layout.simple_spinner_dropdown_item)
            .also { adapter ->
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item)
            rateSpinner.adapter
            rateSpinner.onItemSelectedListener
        }

    }

    override fun onNothingSelected(parent: AdapterView<*>) {

    }
    override fun onItemSelected(parent: AdapterView<*>, view: View,position: Int, id: Long) {

    }
}

编辑：1 - 这是 Logcat

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.debtrearragement, PID: 29305
    java.lang.IllegalStateException: financialSpinner must not be null
        at com.example.debtrearragement.view.ui.debt.AddDebtFragment.onViewCreated(AddDebtFragment.kt:34)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:892)
        at androidx.fragment.app.FragmentManagerImpl.addAddedFragments(FragmentManagerImpl.java:2097)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1871)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1827)
        at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727)
        at androidx.fragment.app.FragmentManagerImpl.run(FragmentManagerImpl.java:150)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
I/Process: Sending signal. PID: 29305 SIG: 9
Application terminated.

编辑：2 - 我刚刚看到它也在编译器上显示。

Answer 1

您不需要为 Spinners 声明新变量，因为您正在使用 kotlin 合成属性。只需删除

private val financialSpinner = financialNameSpinner
private val debtSpinner = debtCategorySpinner
private val rateSpinner = rateTypeSpinner

并在您的代码中将 financialSpinner 替换为 financialNameSpinner，将 debtSpinner 替换为 debtCategorySpinner，将 rateSpinner 替换为 rateTypeSpinner。

您可以从 docs

中找到有关 Kotlin Android 扩展的更多信息

修复警告

您收到此警告是因为 ArrayAdapter.createFromResource 需要一个 Context 对象，而 context(From getContext) returns 一个可为 null 的 Context 对象。您可以做的是使用 !!

将可空对象转换为非空对象

ArrayAdapter.createFromResource(context!!, R.array.financialNameList, android.R.layout.simple_spinner_item)

阅读这篇文章doc 了解更多关于 Kotlin 中的 Null 安全性

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