[英]Where to name my fragment when NullPointerException: name == null
[英]NullPointerException: name == null
我正在开发一个使用Fragments的Android应用程序。 我收到了这个错误。
Caused by: java.lang.NullPointerException: name == null
name == null
是什么意思? 这是完整的日志
08-04 15:02:22.422: E/AndroidRuntime(2499): FATAL EXCEPTION: main
08-04 15:02:22.422: E/AndroidRuntime(2499): java.lang.RuntimeException: Unable to start activity ComponentInfo{fi.peltoset.mikko.home/fi.peltoset.mikko.home.Koti}: android.view.InflateException: Binary XML file line #17: Error inflating class fragment
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.access$600(ActivityThread.java:130)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.os.Handler.dispatchMessage(Handler.java:99)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.os.Looper.loop(Looper.java:137)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.main(ActivityThread.java:4745)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.reflect.Method.invokeNative(Native Method)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.reflect.Method.invoke(Method.java:511)
08-04 15:02:22.422: E/AndroidRuntime(2499): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-04 15:02:22.422: E/AndroidRuntime(2499): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-04 15:02:22.422: E/AndroidRuntime(2499): at dalvik.system.NativeStart.main(Native Method)
08-04 15:02:22.422: E/AndroidRuntime(2499): Caused by: android.view.InflateException: Binary XML file line #17: Error inflating class fragment
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.rInflate(LayoutInflater.java:746)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
08-04 15:02:22.422: E/AndroidRuntime(2499): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:256)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Activity.setContentView(Activity.java:1867)
08-04 15:02:22.422: E/AndroidRuntime(2499): at fi.peltoset.mikko.home.Koti.onCreate(Koti.java:13)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Activity.performCreate(Activity.java:5008)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
08-04 15:02:22.422: E/AndroidRuntime(2499): ... 11 more
08-04 15:02:22.422: E/AndroidRuntime(2499): Caused by: java.lang.NullPointerException: name == null
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.VMClassLoader.findLoadedClass(Native Method)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:354)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.ClassLoader.loadClass(ClassLoader.java:491)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.ClassLoader.loadClass(ClassLoader.java:461)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Fragment.instantiate(Fragment.java:574)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Fragment.instantiate(Fragment.java:552)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Activity.onCreateView(Activity.java:4656)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:680)
08-04 15:02:22.422: E/AndroidRuntime(2499): ... 21 more
这是一个名为Navigation
的类。 它扩展了android.app.Fragment
。
在它的onCreateView
方法中,我膨胀布局并返回它。 在onActivityCreated
方法中,我检查布局是否有两个窗格(我有不同设备的不同布局),并根据我添加onClickListeners到这些。
我的代码看起来像这样。
public class Navigation extends Fragment {
private OnItemSelectedListener listener;
private boolean dualPane = false;
public interface OnItemSelectedListener {
public void onMenuItemSelected(int fragmentId);
}
public void onAttach(Activity activity) {
super.onAttach(activity);
if(activity instanceof OnItemSelectedListener) {
this.listener = (OnItemSelectedListener) activity;
} else {
...
}
}
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_navigation, container, false);
return view;
}
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
View contentPane = getActivity().findViewById(R.id.contentFragment);
dualPane = contentPane != null && contentPane.getVisibility() == View.VISIBLE;
if(dualPane) {
final ListView menu = (ListView) getActivity().findViewById(R.id.valikko);
menu.setChoiceMode(ListView.CHOICE_MODE_SINGLE);
String[] texts = new String[] {
...
};
ArrayList<MenuItem> items = new ArrayList<MenuItem>();
items.add(new MenuItem("Home", R.drawable.koti2));
...
ImageArrayAdapter adapter = new ImageArrayAdapter(getActivity(), items, texts);
menu.setAdapter(adapter);
menu.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String item = ((TextView) view.findViewById(R.id.label)).getText().toString();
listener.onMenuItemSelected(0); // TODO ...
}
});
} else {
ImageView btnYleiskatsaus = (ImageView) getActivity().findViewById(R.id.btnYleiskatsaus);
...
btnYleiskatsaus.setOnClickListener(onMenuClikkedListener);
...
}
}
private OnClickListener onMenuClikkedListener = new OnClickListener() {
@Override
public void onClick(View v) {
...
}
};
}
布局文件layout-sw720dp-land/activity_navigation.xml
看起来如此
<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:background="@color/pressed_koti"
android:orientation="vertical" >
<ListView
android:id="@+id/valikko"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" >
</ListView>
</LinearLayout>
这是activity_koti.xml
文件。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<fragment
android:id="@+id/menuFragment"
android:layout_width="300dp"
android:layout_height="match_parent"
class="fi.peltoset.mikko.home.Navigation" />
<fragment
android:id="@+id/contentFragment"
android:layout_width="fill_parent"
android:layout_height="match_parent" />
</LinearLayout>
我在Android 4.1.2的模拟器上运行应用程序。
导致这些错误的原因是什么?如何解决?
您应该使用android:name
指向您的片段而不是class
,还需要为您的第二个片段包含相同的属性,这将解释name==null
。
编辑: 显然类可以与android:name互换 ,但我会遵循文档使用的内容。
它应该是;
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<fragment
android:id="@+id/menuFragment"
android:layout_width="300dp"
android:layout_height="match_parent"
android:name="fi.peltoset.mikko.home.Navigation" />
<fragment
android:id="@+id/contentFragment"
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:name="I NEED A NAME" />
</LinearLayout>
http://developer.android.com/training/basics/fragments/creating.html#AddInLayout
在XML文件中添加片段时,需要为其指定name
属性。 这就是为什么它说“name = null”,因为你没有这样做。
有关更多信息,请参阅添加片段的指南 。
如果您在FragmentActivity
引用它,请尝试在activity_koti.xml
的第二个片段中添加一个class
。
或者,正如Robadob所说,将android:name:"your.path.YourName"
到两者中。
在有趣的附加信息class
VS android:name
中XML引用Fragment
Ş 这里 。
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