在我的主要活动中的onCreate方法中,我想将适配器设置为listview,如下所示:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editTxt = (EditText) findViewById(R.id.msg);
btn = (Button) findViewById(R.id.addNom);
list = (ListView) findViewById(R.id.list_item);
arrayList = new ArrayList<String>();
adapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_spinner_item, arrayList);
list.setAdapter(adapter);
}
我在
获得了一个nullpointer异常list.setAdapter()
因为
后列表为空list = (ListView) this.findViewById(R.id.list_item);
我假设在任何null对象上调用方法都会导致问题;我怎么能绕过这个?应该用List填充ListView吗?我没有正确实例化ListView对象吗?
这是stacktrace:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ciltkick.nom/com.example.ciltkick.nom.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2071)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2096)
at android.app.ActivityThread.access$600(ActivityThread.java:138)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1207)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:213)
at android.app.ActivityThread.main(ActivityThread.java:4787)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.ciltkick.nom.MainActivity.onCreate(MainActivity.java:52)
at android.app.Activity.performCreate(Activity.java:5008)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2035)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2096)
at android.app.ActivityThread.access$600(ActivityThread.java:138)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1207)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:213)
at android.app.ActivityThread.main(ActivityThread.java:4787)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
at dalvik.system.NativeStart.main(Native Method)
这是布局:
<TableLayout 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"
android:baselineAligned="false">
<TableRow
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<EditText android:id="@+id/msg"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:hint="@string/msg"
android:layout_weight="1"/>
<Button
android:id="@+id/addNom"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/button_send"
android:onClick="addNom"/>
</TableRow>
<TableRow
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_weight="1"
android:layout_gravity="center_vertical">
<ListView android:id="@+id/list_item"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</TableRow>
</TableLayout>
答案 0 :(得分:0)
您的问题是在getApplicationContext
中呼叫onCreate
,请参阅this question。
作为解决方案,您可以这样做:
adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, arrayList);
答案 1 :(得分:0)
我修复了这个问题,原因是布局中的片段结构不佳;代码很好。谢谢!