创建片段时的NPE [英] NPE when creating a fragment
问题描述
我正在使用 sensorEventlitener
创建一个有关 Fragment
的示例.mainactivity托管 fragment
,如下代码所示,但是在运行时,我收到以下发布的 logcat
错误.
i am creating an example about Fragment
with sensorEventlitener
. the mainactivity hosts the fragment
as shown below in the code, but at run time i receive the below posted logcat
Errors.
MainActivity :
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_activity);
initViews();
}
private void initViews() {
// TODO Auto-generated method stub
View frag1 = findViewById(R.id.frag_1);
FragmentManager fMgr = getFragmentManager();
FragmentTransaction fragmentTransaction = fMgr.beginTransaction();
fragmentTransaction.replace(R.id.frag_1, new Frag1());
fragmentTransaction.commit();
}
}
Frag1 :
public class Frag1 extends Fragment implements SensorEventListener {
private SensorManager sensorManager;
TextView tvAccX;
TextView tvAccY;
TextView tvAccZ;
Button btnSend;
@Override
public void onAttach(Activity activity) {
// TODO Auto-generated method stub
super.onAttach(activity);
sensorManager = (SensorManager) getActivity().getSystemService(Context.SENSOR_SERVICE);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
View view = inflater.inflate(R.layout.frag_1, container, false);
tvAccX = (TextView) view.findViewById(R.id.tv_accX_value);
tvAccY = (TextView) view.findViewById(R.id.tv_accY_value);
tvAccZ = (TextView) view.findViewById(R.id.tv_accZ_value);
btnSend = (Button) view.findViewById(R.id.btn_send);
return view;
}
@Override
public void onResume() {
// TODO Auto-generated method stub
super.onResume();
Sensor accSensor = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
sensorManager.registerListener(this, accSensor, sensorManager.SENSOR_DELAY_FASTEST);
}
@Override
public void onPause() {
// TODO Auto-generated method stub
super.onPause();
sensorManager.unregisterListener(this);
}
@Override
public void onSensorChanged(SensorEvent event) {
// TODO Auto-generated method stub
switch (event.sensor.getType()) {
case Sensor.TYPE_ACCELEROMETER:
showAccReadings(event);
break;
default:
break;
}
}
private void showAccReadings(SensorEvent event) {
// TODO Auto-generated method stub
float[] values = event.values;
float x = values[0];
float y = values[1];
float z = values[2];
tvAccX.setText(String.valueOf(x));
tvAccY.setText(String.valueOf(y));
tvAccZ.setText(String.valueOf(z));
}
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
// TODO Auto-generated method stub
}
}
mainActivity.xml :
<RelativeLayout 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"
tools:context="${relativePackage}.${activityClass}">
<fragment
android:id="@+id/frag_1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"/>
<fragment
android:id="@+id/frag_2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="50dp"
android:layout_centerHorizontal="true"
android:layout_below="@+id/frag_1"/>
</RelativeLayout>
Frag1.xml :
<?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:id="@+id/tv_accX_label"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentStart="true"
android:text="Acc[X]: "/>
<TextView
android:id="@+id/tv_accX_value"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_toRightOf="@+id/tv_accX_label"/>
<TextView
android:id="@+id/tv_accY_label"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentStart="true"
android:layout_below="@+id/tv_accX_label"
android:text="Acc[Y]: "/>
<TextView
android:id="@+id/tv_accY_value"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_toRightOf="@+id/tv_accY_label"/>
<TextView
android:id="@+id/tv_accZ_label"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentStart="true"
android:layout_below="@+id/tv_accY_label"
android:text="Acc[Z]: "/>
<TextView
android:id="@+id/tv_accZ_value"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_toRightOf="@+id/tv_accZ_label"/>
<Button
android:id="@+id/btn_send"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/tv_accZ_label"
android:gravity="center_vertical|center_horizontal"
android:text="send to frag_2"/>
</RelativeLayout>
LogCat :
01-23 15:25:11.200: E/AndroidRuntime(7195): Process: com.example.fragmentcommunication_00, PID: 7195
01-23 15:25:11.200: E/AndroidRuntime(7195): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fragmentcommunication_00/com.example.fragmentcommunication_00.MainActivity}: android.view.InflateException: Binary XML file line #7: Error inflating class fragment
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2282)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2340)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.ActivityThread.access$800(ActivityThread.java:157)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.os.Handler.dispatchMessage(Handler.java:102)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.os.Looper.loop(Looper.java:157)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.ActivityThread.main(ActivityThread.java:5293)
01-23 15:25:11.200: E/AndroidRuntime(7195): at java.lang.reflect.Method.invokeNative(Native Method)
01-23 15:25:11.200: E/AndroidRuntime(7195): at java.lang.reflect.Method.invoke(Method.java:515)
01-23 15:25:11.200: E/AndroidRuntime(7195): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
01-23 15:25:11.200: E/AndroidRuntime(7195): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
01-23 15:25:11.200: E/AndroidRuntime(7195): at dalvik.system.NativeStart.main(Native Method)
01-23 15:25:11.200: E/AndroidRuntime(7195): Caused by: android.view.InflateException: Binary XML file line #7: Error inflating class fragment
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:719)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.view.LayoutInflater.rInflate(LayoutInflater.java:761)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.view.LayoutInflater.inflate(LayoutInflater.java:498)
01-2 3 15:25:11.200: E/AndroidRuntime(7195): at android.view.LayoutInflater.inflate(LayoutInflater.java:398)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.view.LayoutInflater.inflate(LayoutInflater.java:354)
01-23 15:25:11.200: E/AndroidRuntime(7195): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:340)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.Activity.setContentView(Activity.java:1973)
01-23 15:25:11.200: E/AndroidRuntime(7195): at com.example.fragmentcommunication_00.MainActivity.onCreate(MainActivity.java:17)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.Activity.performCreate(Activity.java:5389)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2246)
01-23 15:25:11.200: E/AndroidRuntime(7195): ... 11 more
01-23 15:25:11.200: E/AndroidRuntime(7195): Caused by: java.lang.NullPointerException: name == null
01-23 15:25:11.200: E/AndroidRuntime(7195): at java.lang.VMClassLoader.findLoadedClass(Native Method)
01-23 15:25:11.200: E/AndroidRuntime(7195): at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:350)
01-23 15:25:11.200: E/AndroidRuntime(7195): at java.lang.ClassLoader.loadClass(ClassLoader.java:487)
01-23 15:25:11.200: E/AndroidRuntime(7195): at java.lang.ClassLoader.loadClass(ClassLoader.java:457)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.Fragment.instantiate(Fragment.java:583)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.Fragment.instantiate(Fragment.java:561)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.app.Activity.onCreateView(Activity.java:4927)
01-23 15:25:11.200: E/AndroidRuntime(7195): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:695)
更新:
Frag1.xml :
<fragment
android:name="com.example.fragmentcommunication_00.Frag1"
android:id="@+id/frag_1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"/>
记录:
01-23 15:37:42.980: E/AndroidRuntime(8267): FATAL EXCEPTION: main
01-23 15:37:42.980: E/AndroidRuntime(8267): Process: com.example.fragmentcommunication_00, PID: 8267
01-23 15:37:42.980: E/AndroidRuntime(8267): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fragmentcommunication_00/com.example.fragmentcommunication_00.MainActivity}: android.view.InflateException: Binary XML file line #14: Error inflating class fragment
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2282)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2340)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.ActivityThread.access$800(ActivityThread.java:157)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.os.Handler.dispatchMessage(Handler.java:102)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.os.Looper.loop(Looper.java:157)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.ActivityThread.main(ActivityThread.java:5293)
01-23 15:37:42.980: E/AndroidRuntime(8267): at java.lang.reflect.Method.invokeNative(Native Method)
01-23 15:37:42.980: E/AndroidRuntime(8267): at java.lang.reflect.Method.invoke(Method.java:515)
01-23 15:37:42.980: E/AndroidRuntime(8267): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
01-23 15:37:42.980: E/AndroidRuntime(8267): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
01-23 15:37:42.980: E/AndroidRuntime(8267): at dalvik.system.NativeStart.main(Native Method)
01-23 15:37:42.980: E/AndroidRuntime(8267): Caused by: android.view.InflateException: Binary XML file line #14: Error inflating class fragment
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:719)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.view.LayoutInflater.rInflate(LayoutInflater.java:761)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.view.LayoutInflater.inflate(LayoutInflater.java:498)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.view.LayoutInflater.inflate(LayoutInflater.java:398)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.view.LayoutInflater.inflate(LayoutInflater.java:354)
01-23 15:37:42.980: E/AndroidRuntime(8267): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:340)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.Activity.setContentView(Activity.java:1973)
01-23 15:37:42.980: E/AndroidRuntime(8267): at com.example.fragmentcommunication_00.MainActivity.onCreate(MainActivity.java:17)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.Activity.performCreate(Activity.java:5389)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2246)
01-23 15:37:42.980: E/AndroidRuntime(8267): ... 11 more
01-23 15:37:42.980: E/AndroidRuntime(8267): Caused by: java.lang.NullPointerException: name == null
01-23 15:37:42.980: E/AndroidRuntime(8267): at java.lang.VMClassLoader.findLoadedClass(Native Method)
01-23 15:37:42.980: E/AndroidRuntime(8267): at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:350)
01-23 15:37:42.980: E/AndroidRuntime(8267): at java.lang.ClassLoader.loadClass(ClassLoader.java:487)
01-23 15:37:42.980: E/AndroidRuntime(8267): at java.lang.ClassLoader.loadClass(ClassLoader.java:457)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.Fragment.instantiate(Fragment.java:583)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.Fragment.instantiate(Fragment.java:561)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.app.Activity.onCreateView(Activity.java:4927)
01-23 15:37:42.980: E/AndroidRuntime(8267): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:695)
推荐答案
似乎您缺少活动布局文件中 fragment
标签中的 name
属性.基本上有两种方法可以将Fragment扩展到您的视图层次结构中:
It looks like you are missing the name
attribute in your fragment
tags in your activity layout file. There are basically two ways to get a Fragment inflated into your view hierarchy:
- 在布局XML中指定所有内容
- 在您的Java代码中加载片段
您似乎已经将这两种范例混合在一起,这就是给您造成麻烦的原因.
It appears that you have mixed these two paradigms together, which is what is causing you the trouble.
为了在布局XML中执行所有操作,必须指定 name
属性.所以,像这样:
In order to do everything in the layout XML, you must specify the name
attribute. So, something like this:
<fragment
android:name="com.my.package.for.Frag1"
android:id="@+id/frag_1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"/>
然后您就可以从您的 initViews()
方法中删除该代码,因为它不再需要.
You could then remove the code from your initViews()
method as it is no longer necessary.
如果相反,您希望使用代码完成所有操作,则必须更改布局以指定将片段插入到的空容器.例如,使用 FrameLayout
而不是 fragment
标签,如下所示:
If, instead, you would prefer to do everything in code, then you must change your layout to specify an empty container where the Fragment will go. For example, use a FrameLayout
instead of a fragment
tag, like this:
<FrameLayout
android:id="@+id/frag_1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"/>
这篇关于创建片段时的NPE的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!