【发布时间】：2016-07-31 18:18:03
【问题描述】：
美好的一天！
我很难解决这个问题。我尝试实现接口、可打包对象和捆绑包，只是为了与片段进行通信。但是在我运行我的代码之后，它每次在 Fragment 类中都会出现 NullPointerException。这是错误：
07-31 18:09:42.052 4776-4776/bwrt.monsters.android.com.blesswhoreadthis E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{bwrt.monsters.android.com.blesswhoreadthis/bwrt.monsters.android.com.blesswhoreadthis.Activity.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:2059)
at android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:2084)
at android.app.ActivityThread.access$600(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
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:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at wrt.monsters.android.com.blesswhoreadthis.Fragment.GenesisFragment.onCreate(GenesisFragment.java:58)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:796)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1035)
at android.app.BackStackRecord.run(BackStackRecord.java:635)
at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1397)
at android.app.Activity.performStart(Activity.java:5017)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2032)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access$600(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
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:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
这是我的片段类：
public class GenesisFragment extends Fragment {
Context mContext;
ListView lv;
ArrayList<Bible> verseList=null;
VerseAdapter verseAdapter;
displayDataInterface listeners;
public interface displayDataInterface {
Bundle displayData();
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof displayDataInterface) {
this.listeners= (displayDataInterface) context;
}else {
throw new ClassCastException(context.toString()+" must implement the NEEDED INTERFACE!");
}
}
/** @Override */
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle bundle=listeners.displayData();
if (bundle.isEmpty()) {
Log.e("BUNDLE","EMPTY");
}else {
verseList= bundle.getParcelableArrayList("verseValues");
}
verseAdapter= new VerseAdapter(mContext,verseList);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v= inflater.inflate(R.layout.fragment_genesis, container, false);
return v;
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
lv=(ListView)getActivity().findViewById(R.id.listview_genesis);
lv.setAdapter(verseAdapter);
verseAdapter.notifyDataSetChanged();
}
}
我的 MainActivity Class 部分，我在接口方法中实现了 Bundles (_bibleValues- 一个 ArrayList)：
/** Interface Generated Methods*/
@Override
public Bundle displayData() {
GenesisFragment gFragment= new GenesisFragment();
Bundle args= new Bundle();
args.putParcelableArrayList("verseValues",_bibleValues); //Make the Object class Parcelable 1st
gFragment.setArguments(args);
return args;
}
我的对象等级：
public class Bible implements Parcelable{
private int id;
private int book;
private int chapter;
private int verseCount;
private String verseContent;
/** Constructors */
public Bible(int _id,int _book, int _chapter,int _verseCount, String _verseContent) {
this.id=_id;
this.book=_book;
this.chapter=_chapter;
this.verseCount=_verseCount;
this.verseContent=_verseContent;
}
protected Bible(Parcel in) {
id = in.readInt();
book = in.readInt();
chapter = in.readInt();
verseCount = in.readInt();
verseContent = in.readString();
}
public static final Creator<Bible> CREATOR = new Creator<Bible>() {
@Override
public Bible createFromParcel(Parcel in) {
return new Bible(in);
}
@Override
public Bible[] newArray(int size) {
return new Bible[size];
}
};
/** Getters and Setters */
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getBook() {
return book;
}
public void setBook(int book) {
this.book = book;
}
public int getChapter() {
return chapter;
}
public void setChapter(int chapter) {
this.chapter = chapter;
}
public int getVerseCount() {
return verseCount;
}
public void setVerseCount(int verseCount) {
this.verseCount = verseCount;
}
public String getVerseContent() {
return verseContent;
}
public void setVerseContent(String verseContent) {
this.verseContent = verseContent;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeInt(id);
dest.writeInt(book);
dest.writeInt(chapter);
dest.writeInt(verseCount);
dest.writeString(verseContent);
}
}
每次我运行程序时，它总是在 Fragment 类的 onCreate 中指出错误。谁能向我解释这个错误的根本原因并建议我防止这种情况发生的想法？
提前致谢！
【问题讨论】：
-
_bibleValues的类型是什么？ -
@skywall- 一个对象先生。因为我有一个可打包的对象，所以只是为了实现 Bundle 方法。
-
我的对象由 4 个整数和 1 个字符串组成。
-
在这种情况下说
Object非常具有误导性。Object是 Java 基类。下次称它为“我的班级圣经”。
标签： android android-fragments arraylist interface nullpointerexception