Cursor, der nullpointer wirft, wenn er vom Inhaltsanbieter

Question

aufgerufen wird

Ich versuche, Daten aus zwei verschiedenen Tabellen mit einem LoaderManager in einem ListFragment abzufragen. Meine Tabellen haben definitiv Daten, die ich überprüft habe, aber aus irgendeinem Grund gibt meine Abfrage/Cursor null zurück. Ich vermute, es ist ein Syntaxproblem, aber ich bin mir nicht ganz sicher. Ich habe die gleiche Abfrage in MySql Workbench ausgeführt, und es hat funktioniert. Iv versucht, die Abfrage wie folgt ausgeführt werden:

cursor = db.query("Customer, Appointment", new String[]{"fullname", "physicalAddress", "date","time"}, "Customer.ID IN(?)", new String[]{"select customerID from Appointment"},null,null,null);

und diese:

cursor = db.rawQuery("select fullName, physicalAddress, date, time from Customer, Appointment where Customer.ID IN(select customerID from Appointment);", null);

Aber jedes dieser Codezeile lautet:

cursor.setNotificationUri(getContext().getContentResolver(), uri);

ich erhalte eine Nullpointer . Falls dies etwas bedeutet, verwende ich kein FrameLayout und füge mein ListFragment dynamisch hinzu. Iv definiert es in der XML-Datei Aktivitäten. Jede Hilfe wird geschätzt. Bitte lassen Sie mich wissen, wenn ich etwas ausgelassen habe.

DatabaseContentProvider:

package com.venon.nakomangsp; 

import android.content.ContentProvider; 
import android.content.ContentValues; 
import android.content.UriMatcher; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.net.Uri; 
import android.support.annotation.Nullable; 

@SuppressWarnings("ConstantConditions") 
public class DatabaseContentProvider extends ContentProvider { 

DatabaseHelper dbHelper; 
private static final String PROVIDER_NAME = "com.venon.nakomangsp.databasecontentprovider"; 
private static final UriMatcher uriMatcher; 
public static final Uri CUSTOMER_URI = Uri.parse("content://"+ PROVIDER_NAME+"/Customer"); 
private static final int CUSTOMER_CODE = 1; 
public static final Uri APPOINTMENT_URI = Uri.parse("content://" + PROVIDER_NAME + "/Appointment"); 
private static final int APPOINTMENT_CODE = 2; 
public static final Uri APPOINTMENT_VIEW_URI = Uri.parse("content://" + PROVIDER_NAME + "/AppointmentView"); 
private static final int APPOINTMENT_VIEW_CODE = 3; 

static{ 
    uriMatcher = new UriMatcher(UriMatcher.NO_MATCH); 
    uriMatcher.addURI(PROVIDER_NAME,"Customer", CUSTOMER_CODE); 
    uriMatcher.addURI(PROVIDER_NAME, "Appointment", APPOINTMENT_CODE); 
} 


@Override 
public boolean onCreate() { 
    dbHelper = new DatabaseHelper(getContext()); 
    return true; 
} 

@Nullable 
@Override 
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { 

    SQLiteDatabase db = dbHelper.getWritableDatabase(); 
    Cursor cursor = null; 

    switch(uriMatcher.match(uri)){ 

     case CUSTOMER_CODE: 
      cursor = db.query("Customer", projection, selection, selectionArgs, null, null, sortOrder); 
      break; 

     case APPOINTMENT_CODE: 
      cursor = db.query("Appointment", projection, selection, selectionArgs, null, null, sortOrder); 
      break; 

     case APPOINTMENT_VIEW_CODE://this is the case triggered 
      //cursor = db.rawQuery("select fullName, physicalAddress, date, time from Customer, Appointment where Customer.ID IN(select customerID from Appointment);", null); 

      cursor = db.query("Customer, Appointment", new String[]{"fullname", "physicalAddress", "date","time"}, "Customer.ID IN(?)", new String[]{"select customerID from Appointment"},null,null,null); 

     default: 
      break; 

    } 

    cursor.setNotificationUri(getContext().getContentResolver(), uri); 

    return cursor; 
} 

@Nullable 
@Override 
public Uri insert(Uri uri, ContentValues values) { 

    SQLiteDatabase db = dbHelper.getWritableDatabase(); 

    switch(uriMatcher.match(uri)){ 

     case CUSTOMER_CODE: 
      db.insertOrThrow("Customer", null, values); 
      break; 

     case APPOINTMENT_CODE: 
      db.insertOrThrow("Appointment", null, values); 
      break; 

     default: 
      break; 

    } 

    getContext().getContentResolver().notifyChange(uri, null, false);//set to true when syncadapter hooked up 
    return null; 
} 

@Override 
public int delete(Uri uri, String selection, String[] selectionArgs) { 

    SQLiteDatabase db = dbHelper.getWritableDatabase(); 

    switch(uriMatcher.match(uri)){ 

     case CUSTOMER_CODE: 
      db.delete("Customer", selection, selectionArgs); 
      break; 

     case APPOINTMENT_CODE: 
      db.delete("Appointment", selection, selectionArgs); 
      break; 

     default: 
      break; 

    } 

    getContext().getContentResolver().notifyChange(uri, null, false);//keep as false when hooking up syncadapter 
    return 0; 
} 

@Override 
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { 

    SQLiteDatabase db = dbHelper.getWritableDatabase(); 

    switch(uriMatcher.match(uri)){ 

     case CUSTOMER_CODE: 
      db.update("Customer", values, selection, selectionArgs); 
      break; 

     case APPOINTMENT_CODE: 
      db.update("Appointment", values, selection, selectionArgs); 
      break; 

     default: 
      break; 

    } 
    getContext().getContentResolver().notifyChange(uri, null, false); 
    return 0; 
} 

@Nullable 
@Override 
public String getType(Uri uri) { 
    return null; 
} 
} 

Telefonvorwahl:

package com.venon.nakomangsp; 


import android.content.Intent; 
import android.database.Cursor; 
import android.os.Bundle; 
import android.support.v4.app.ListFragment; 
import android.support.v4.app.LoaderManager; 
import android.support.v4.content.CursorLoader; 
import android.support.v4.content.Loader; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ListView; 
import android.widget.SimpleCursorAdapter; 


public class AppointmentListFragment extends ListFragment implements  LoaderManager.LoaderCallbacks<Cursor> { 
SimpleCursorAdapter adapter; 

public static AppointmentListFragment newInstance() { 
    AppointmentListFragment fragment = new AppointmentListFragment(); 

    return fragment; 
} 

public AppointmentListFragment() { 
    // Required empty public constructor 
} 

@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) { 

    View view = inflater.inflate(R.layout.fragment_appointment_list, container, false); 

    String[] from = {"fullName", "physicalAddress", "date", "time"}; 
    int[] to = {R.id.customerName_lv, R.id.physicalAddress_lv, R.id.date_lv, R.id.time_lv}; 
    adapter = new SimpleCursorAdapter(getContext(), R.layout.appointment_list, null, from, to, 0); 
    setListAdapter(adapter); 

    getActivity().getSupportLoaderManager().initLoader(0, null, AppointmentListFragment.this); 

    return view; 
} 

@Override 
public void onListItemClick(ListView l, View v, int position, long id) { 
    super.onListItemClick(l, v, position, id); 

    getActivity().startActivity(new Intent(getContext(), AppointmentViewActivity.class)); 
} 

@Override 
public Loader<Cursor> onCreateLoader(int i, Bundle bundle) { 
    //this is the calling line 
    return new CursorLoader(getContext(), DatabaseContentProvider.APPOINTMENT_VIEW_URI, null, null, null, null); 
} 

@Override 
public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor cursor) { 

    adapter.swapCursor(cursor); 
} 

@Override 
public void onLoaderReset(Loader<Cursor> cursorLoader) { 
    adapter.swapCursor(null); 
} 


} 

Answer 1

wenn Ihr uri nicht eines der Elemente drei Fall übereinstimmen, werden Cursor null sein und Sie erhalten eine NPE:

switch(uriMatcher.match(uri)){ 

    case CUSTOMER_CODE: 
     cursor = db.query("Customer", projection, selection, selectionArgs, null, null, sortOrder); 
     break; 

    case APPOINTMENT_CODE: 
     cursor = db.query("Appointment", projection, selection, selectionArgs, null, null, sortOrder); 
     break; 

    case APPOINTMENT_VIEW_CODE://this is the case triggered 
     //cursor = db.rawQuery("select fullName, physicalAddress, date, time from Customer, Appointment where Customer.ID IN(select customerID from Appointment);", null); 

     cursor = db.query("Customer, Appointment", new String[]{"fullname", "physicalAddress", "date","time"}, "Customer.ID IN(?)", new String[]{"select customerID from Appointment"},null,null,null); 

    default: 
     break; 

} 

cursor.setNotificationUri(getContext().getContentResolver(), uri); 

Der beste Weg ist, eine IllegalArgument-Ausnahme in default zu werfen.

default: 
     throw new IllegalArgumentException("unknown uri");