我有一个非活动课，我想访问我保存在片段中的variables。我可以在其他片段/活动中使用这些prefs，因此它们正在工作。当我尝试在我的non_Activity类中将prefvalues分配给public class VorgangDataSource {
Context mcontext;
float lbcount;
float rbcount;
float bcount;
SharedPreferences sharedPreferences;
SharedPreferences sharedPreferences1;
SharedPreferences sharedPreferences2;
private static final String LOG_TAG = VorgangDataSource.class.getSimpleName();
public SQLiteDatabase database;
private VorgangDbHelper dbHelper;
private String[] columns = {
VorgangDbHelper.COLUMN_ID,
VorgangDbHelper.COLUMN_START,
VorgangDbHelper.COLUMN_STOP,
VorgangDbHelper.COLUMN_LEFTB,
VorgangDbHelper.COLUMN_RIGHTB,
VorgangDbHelper.COLUMN_BOTTLE
};
public VorgangDataSource(Context context) {
Log.d(LOG_TAG, "DataSource erzeugt dbHelper!");
dbHelper = VorgangDbHelper.getInstance();
this.mcontext = context;
this.sharedPreferences = mcontext.getSharedPreferences("FILELB",Context.MODE_PRIVATE);
this.sharedPreferences1 = mcontext.getSharedPreferences("FILERB",Context.MODE_PRIVATE);
this.sharedPreferences2 = mcontext.getSharedPreferences("FILEBO",Context.MODE_PRIVATE);
this.lbcount = sharedPreferences.getFloat("KEYLB",0);
this.rbcount = sharedPreferences1.getFloat("KEYRB",0);
this.bcount = sharedPreferences2.getFloat("KEYBO",0);
}
public void open() {
Log.d(LOG_TAG, "Eine Referenz auf die Datenbank wird jetzt angefragt.");
database = dbHelper.getWritableDatabase();
Log.d(LOG_TAG, "Datenbank-Referenz erhalten. Pfad zur Datenbank: " + database.getPath());
}
public void close() {
dbHelper.close();
Log.d(LOG_TAG, "Datenbank mit Hilfe des DbHelpers geschlossen.");
}
public VorgangDataSource open(boolean readOnly) throws SQLException {
dbHelper = VorgangDbHelper.getInstance();
if(readOnly)
database = dbHelper.getReadableDatabase();
else
database = dbHelper.getWritableDatabase();
return this;
}
}
时，无论我改变了什么，我都会得到一个nullpointerexception（我已经在堆栈上阅读了多个主题，没有任何工作）。
06-15 08:28:47.816 12806-12806/com.example... E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example PID: 12806
java.lang.NullPointerException
at com.example...VorgangDataSource.<init>(VorgangDataSource.java:169)
at com.example...frag_anzeigen.<init>(frag_anzeigen.java:53)
at com.example...MainActivity.onNavigationItemSelected(MainActivity.java:117)
at android.support.design.widget.NavigationView$1.onMenuItemSelected(NavigationView.java:151)
at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:811)
at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)
at android.support.design.internal.NavigationMenuPresenter$1.onClick(NavigationMenuPresenter.java:318)
at android.view.View.performClick(View.java:4748)
at android.view.View$PerformClick.run(View.java:19535)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5679)
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:1291)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
at dalvik.system.NativeStart.main(Native Method)
错误日志：
public class frag_anzeigen extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private OnFragmentInteractionListener mListener;
private static final String TAG = frag_anlegen.class.getSimpleName();
private static final String FILENAME = TAG + ".kdf";
private List valueList = new ArrayList <String>();
final VorgangDataSource dataSource = new VorgangDataSource(getActivity());
ArrayAdapter<vorgangsdaten> VorgangArrayAdapter;
List<vorgangsdaten> vorgangsdatenList;
public frag_anzeigen() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment frag_anzeigen.
*/
// TODO: Rename and change types and number of parameters
public static frag_anzeigen newInstance(String param1, String param2) {
frag_anzeigen fragment = new frag_anzeigen();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final View anzeigen = inflater.inflate(R.layout.frag_anzeigen,container,false);
anzeigen.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
if(event.getAction()==MotionEvent.ACTION_DOWN)
{
close();
}
return true;
}
});
Log.d(TAG,"Die Datenquelle wird geöffnet!");
dataSource.open();
vorgangsdatenList = dataSource.getAllVorgangsDaten();
VorgangArrayAdapter = new ArrayAdapter< >(getActivity(),R.layout.mylistlayout,vorgangsdatenList);
final ListView lv = (ListView)anzeigen.findViewById(R.id.listView);
lv.setAdapter(VorgangArrayAdapter);
//lv.setItemsCanFocus(false);
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, final int position, final long id) {
String s_id = String.valueOf(id);
Log.d(s_id,"id_in_onitem");
String p_id = String.valueOf(position);
Log.d(p_id,"position_on_item");
final AlertDialog delete = new AlertDialog.Builder(getActivity()).create();
delete.setTitle(getResources().getString(R.string.advice));
delete.setMessage(getResources().getString(R.string.delete2dialog));
delete.setIcon(R.drawable.warning);
delete.setButton(DialogInterface.BUTTON_POSITIVE, getResources().getString(R.string.ok), new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
vorgangsdatenList.remove(position);
dataSource.deleteRow(id);
VorgangArrayAdapter.notifyDataSetChanged();
Toast.makeText(getActivity(), getResources().getString(R.string.eventdeleted), Toast.LENGTH_SHORT).show();
}
});
delete.setButton(DialogInterface.BUTTON_NEGATIVE, getResources().getString(R.string.cancel), new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
delete.closeOptionsMenu();
}
});
delete.show();
}
});
return anzeigen;
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p/>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
@Override
public void onDestroyView() {
super.onDestroyView();
}
public void close (){
FragmentManager fm = getFragmentManager();
FragmentTransaction transaction = fm.beginTransaction();
transaction.setCustomAnimations(R.anim.slide_in_up,R.anim.slide_out_up);
transaction.remove(this);
transaction.commit();
}
}
片段级
html5lib答案 0 :(得分：1)
问题出在这一行
final VorgangDataSource dataSource = new VorgangDataSource(getActivity());
这里getActivity（）返回null，因为如果尚未调用相应片段的onAttach。所以从那里删除该行并写入onAttach方法或片段类的onCreate方法。
希望这会对你有所帮助。