语言: Kotlin 目标:最新的sdk
那么这里实际发生了什么，
我的底部导航栏有四个选项卡，每个选项卡都有一个 fragment 。
在第一个 fragment 中，我试图显示一个静态 ListView，它使应用程序强制关闭。
主要 Activity .kt
import android.os.Bundle
import android.widget.ArrayAdapter
import android.widget.ListView
import androidx.appcompat.app.AppCompatActivity
import com.google.android.material.bottomnavigation.BottomNavigationView
import android.widget.TextView
import androidx.fragment.app.Fragment
import android.content.ClipData.Item
import android.widget.ListAdapter
import kotlinx.android.synthetic.main.fragment_rough_calc.*
class MainActivity : AppCompatActivity() {
private lateinit var fragment: Fragment
private lateinit var listView: ListView
private val onNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
when (item.itemId) {
R.id.navigation_rough -> {
//supportFragmentManager.beginTransaction().replace(R.id.fragment_in_rough_calc, PolishCalcFragment()).commit()
supportFragmentManager.beginTransaction().replace(R.id.fragment_container, RoughCalcFragment()).commit()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_polish -> {
supportFragmentManager.beginTransaction().replace(R.id.fragment_container, PolishCalcFragment()).commit()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_saved -> {
supportFragmentManager.beginTransaction().replace(R.id.fragment_container, SavedFragment()).commit()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_settings -> {
supportFragmentManager.beginTransaction().replace(R.id.fragment_container, SettingsFragment()).commit()
return@OnNavigationItemSelectedListener true
}
}
true
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val navView: BottomNavigationView = findViewById(R.id.nav_view)
navView.setOnNavigationItemSelectedListener(onNavigationItemSelectedListener)
listView = findViewById<ListView>(R.id.part_list)
val partList = ArrayList<String>()//Creating an empty arraylist
partList.add("Part A")
partList.add("Part B")
partList.add("Part C")
partList.add("Part D")
partList.add("Part E")
var partAdapterStatic = ArrayAdapter<String>(this, R.layout.part_view, partList)
listView.adapter = partAdapterStatic
supportFragmentManager.beginTransaction().replace(R.id.fragment_container, RoughCalcFragment()).commit()
}
}
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:id = "@+id/container"
android:layout_width = "match_parent"
android:layout_height = "match_parent"
tools:context = ".MainActivity">
<FrameLayout
android:id = "@+id/fragment_container"
android:layout_width = "match_parent"
android:layout_height = "wrap_content"
app:layout_constraintEnd_toEndOf = "parent"
app:layout_constraintBottom_toTopOf = "parent"
app:layout_constraintTop_toTopOf = "parent"
app:layout_constraintStart_toStartOf = "parent"/>
<com.google.android.material.bottomnavigation.BottomNavigationView
style = "@style/Widget.MaterialComponents.BottomNavigationView.Colored"
android:id = "@+id/nav_view"
android:layout_width = "wrap_content"
android:layout_height = "wrap_content"
app:layout_constraintBottom_toBottomOf = "parent"
app:layout_constraintLeft_toLeftOf = "parent"
app:layout_constraintRight_toRightOf = "parent"
app:menu = "@menu/bottom_nav_menu"
android:elevation = "0px"
app:itemIconTint = "@drawable/bottom_navigation_colors"
app:itemTextColor = "@drawable/bottom_navigation_colors"/>
</androidx.constraintlayout.widget.ConstraintLayout>
fragment _1.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android = "http://schemas.android.com/apk/res/android"
xmlns:tools = "http://schemas.android.com/tools"
android:layout_width = "match_parent"
android:layout_height = "match_parent"
xmlns:app = "http://schemas.android.com/apk/res-auto"
android:background = "@color/colorPrimary"
android:paddingTop="175dp"
android:paddingLeft="15dp"
android:paddingRight="15dp">
<com.google.android.material.textfield.TextInputLayout
style="@style/Widget.MaterialComponents.TextInputLayout.FilledBox"
android:id="@+id/rawStoneWeight"
app:boxCornerRadiusBottomEnd ="10dp"
app:boxCornerRadiusBottomStart="10dp"
app:boxCornerRadiusTopStart="10dp"
app:boxCornerRadiusTopEnd="10dp"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="@string/rough_weight_input_hint"
app:hintAnimationEnabled="true">
<com.google.android.material.textfield.TextInputEditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="numberDecimal"
android:autoSizeMaxTextSize="5dp"
android:textStyle="bold"
android:maxLength="6"/>
</com.google.android.material.textfield.TextInputLayout>
<androidx.appcompat.widget.AppCompatTextView
android:layout_width = "wrap_content"
android:layout_height = "wrap_content"
android:text="@string/rough_weight_input_suffix"
android:layout_alignParentEnd="true"
android:paddingTop="35dp"
android:paddingEnd="17dp"
android:paddingStart="17dp"
android:textStyle="bold" />
<ListView
android:id="@+id/part_list"
android:layout_below="@id/rawStoneWeight"
android:paddingBottom="90dp"
android:layout_width = "match_parent"
android:layout_height = "wrap_content" >
</ListView>
</RelativeLayout>
日志错误:
2019-02-24 17:51:26.876 22239-22239/in.navkargems.tools E/AndroidRuntime: FATAL EXCEPTION: main
Process: in.navkargems.tools, PID: 22239
java.lang.RuntimeException: Unable to start activity ComponentInfo{in.navkargems.tools/in.navkargems.tools.MainActivity}: java.lang.IllegalStateException: findViewById<ListView>(R.id.part_list) must not be null
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2951)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3086)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1816)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6718)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.IllegalStateException: findViewById<ListView>(R.id.part_list) must not be null
at in.navkargems.tools.MainActivity.onCreate(MainActivity.kt:48)
at android.app.Activity.performCreate(Activity.java:7144)
at android.app.Activity.performCreate(Activity.java:7135)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2931)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3086)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1816)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6718)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
请帮我解决这个问题 谢谢大家的宝贵时间(:
最佳答案
你的问题在这里
listView = findViewById<ListView>(R.id.part_list)
你的列表是 fragment 而不是 Activity
所以 listView 将为 Null
所以你必须在 fragment 中定义你的 ListView 并初始化它
关于android - [Android][ListView]无法在 fragment 中显示ListView，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54851843/