Java Android nullpointerException-listview
我见过其他人也有同样的问题,但他们缺少setContentView()。 你知道为什么下面的方法不起作用吗?当我调用setAdapter时发生NPE,因为listView为nullJava Android nullpointerException-listview,java,android,listview,nullpointerexception,Java,Android,Listview,Nullpointerexception,我见过其他人也有同样的问题,但他们缺少setContentView()。 你知道为什么下面的方法不起作用吗?当我调用setAdapter时发生NPE,因为listView为null public class DisplayMessageActivity extends Activity { protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView
public class DisplayMessageActivity extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_display_message);
ArrayList<String> message = getArray();
ListView listView = (ListView) findViewById(R.id.listView);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, message);
listView.setAdapter(adapter);
public类DisplayMessageActivity扩展活动{
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity\u display\u message);
ArrayList消息=getArray();
ListView ListView=(ListView)findViewById(R.id.ListView);
ArrayAdapter=新的ArrayAdapter(这是android.R.layout.simple\u list\u item\u 1,消息);
setAdapter(适配器);
});
activity_main.xml
<LinearLayout 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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:orientation="horizontal"
tools:context=".MainActivity" >
<EditText android:id="@+id/edit_message"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:hint="@string/edit_message" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/button_send"
android:onClick="sendMessage" />
<ListView android:id="@+id/listView"
android:layout_height="match_parent"
android:layout_width="match_parent"/>
<TextView
android:id="@+id/rowTextView"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:padding="10dp"
android:textSize="16sp" >
</TextView>
</LinearLayout>
调用
setContentView时,您正在引用R.layout.activity\u display\u message
,这意味着(ListView)findViewById(R.id.ListView);
将返回null
不要调用setContentView(R.layout.activity\u display\u message)
调用setContentView(R.layout.activity\u main)
是否确实应该在setContentView()中使用R.layout.activity\u display\u message,因为您的布局是activity\u main.xml