java - Android - 使用 ViewGroup 的 NullPointerException

Question

当我使用简单的 TextView 从一个 Activity 转移到另一个 Activity 时 - 它起作用了。 一段代码:

 private RMProject currentProject;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.open_proj);
    Bundle bundle = getIntent().getExtras();
    currentProject = bundle.getParcelable("current");
    TextView textView = (TextView) findViewById(R.id.label_open_project);
    textView.setText("Project "+currentProject.getName());

}

但是，当我将另一个 Activity 与 onCreate() 方法中的下一个代码一起使用时 - 它不起作用并且我收到 NullPointerException。在第 38 行。我检查了一下，我在使用第一段代码时收到了 textView。

public class EventsActivity extends Activity {
private RMProject currentProject;
private ListView listView;
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    EventDBManager.init(this);
    ViewGroup contentView = (ViewGroup) getLayoutInflater().inflate(R.layout.orm_event_list, null);
    listView = (ListView) contentView.findViewById(R.id.ormListView);
    Bundle bundle = getIntent().getExtras();
    currentProject = bundle.getParcelable("current");
    TextView textView = (TextView) findViewById(R.id.ormTextView);
    //38 line - next, which cause exception
    textView.setText("Project "+currentProject.getName());
    Button btn = (Button) contentView.findViewById(R.id.ormButtonAdd);
    setupButton(btn);
    setContentView(contentView);
}
}

我猜是组件布局的问题。 这是我的布局文件:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
<TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:editable="true"
        android:text="Project name"
        android:id="@+id/ormTextView"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true"
        android:layout_marginLeft="90dp"
        android:textSize="20dp"/>
<Button
        android:id="@+id/ormButtonAdd"
        android:layout_alignParentBottom="true"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Add " />
<ListView
        android:id="@+id/ormListView"
        android:layout_above="@id/ormButtonAdd"

        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />
</RelativeLayout>

我收到的异常(exception)情况:

04-15 18:26:29.209 1401-1401/nikolay.rm E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: nikolay.rm, PID: 1401 java.lang.RuntimeException: Unable to start activity ComponentInfo{nikolay.rm/nikolay.rm.activities.EventsActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) at android.app.ActivityThread.access$800(ActivityThread.java:135) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5017) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at nikolay.rm.activities.EventsActivity.onCreate(EventsActivity.java:38) at android.app.Activity.performCreate(Activity.java:5231) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)             at android.app.ActivityThread.access$800(ActivityThread.java:135)             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)             at android.os.Handler.dispatchMessage(Handler.java:102)             at android.os.Looper.loop(Looper.java:136)             at android.app.ActivityThread.main(ActivityThread.java:5017)             at java.lang.reflect.Method.invokeNative(Native Method)             at java.lang.reflect.Method.invoke(Method.java:515)

Answer 1

您在下一行中缺少 contentView 引用

TextView textView = (TextView) findViewById(R.id.ormTextView);

所以解决方法是将其替换为

TextView textView = (TextView) contentView .findViewById(R.id.ormTextView);

希望对你有帮助