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
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
):