kotlin 在android中将arrayAdapter传递给ListViewAdapter

qxsslcnc 于 2022-12-27 发布在 Kotlin

关注(0)|答案(1)|浏览(188)

我有问题，而通过我的arrayAdapter的ListViewAdapter在Android使用Kotlin.错误消息java.lang.NullPointerException：尝试在空对象引用上调用虚方法“void android.widget.ListView.setAdapter(android.widget.ListAdapter)”指示我正在尝试调用对象引用null上的方法。
以下是我的主要活动：

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.ArrayAdapter
import android.widget.ListView

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val lv = findViewById<ListView>(R.id.myList)
        val array = arrayOf("test", "test", "test", "test", "test")
        val myAdapter: ArrayAdapter<String> =
            ArrayAdapter(this, android.R.layout.simple_list_item_1, array)
        lv.adapter = myAdapter
    }
}

布局文件如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/relativeLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingHorizontal="20dp"
    tools:context=".MainActivity">

    <ListView
        android:id="@+id/myList"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginStart="20dp"
        android:layout_marginEnd="20dp" />
</LinearLayout>

这是我得到的错误

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
        at com.example.myapplication5.MainActivity.onCreate(MainActivity.kt:16)
        at android.app.Activity.performCreate(Activity.java:7994)
        at android.app.Activity.performCreate(Activity.java:7978)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:223) 
        at android.app.ActivityThread.main(ActivityThread.java:7656) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 
2022-12-25 14:33:52.075 14422-14438/com.example.myapplication5 W/System: A resource failed to call close.

调试显示myAdapter包含正确的array值

kotlin

来源：https://stackoverflow.com/questions/74915727/passing-arrayadapter-to-listviewadapter-in-android

1条答案

按热度按时间

dauxcl2d1#

在访问任何视图之前，您必须调用setContentView(<Name of your layout file>)。参见工作示例（在我的示例中，布局文件的名称是activity_main.xml）：

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val lv = findViewById<ListView>(R.id.myList)
        val array = arrayOf("test", "test", "test", "test", "test")
        val myAdapter: ArrayAdapter<String> =
            ArrayAdapter(this, android.R.layout.simple_list_item_1, array)
        lv.adapter = myAdapter
    }
}

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kotlin 在android中将arrayAdapter传递给ListViewAdapter

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