内容提供者中的query（）方法

Question

我说的是运行时错误

“ java.lang.NullPointerException：尝试在空对象引用”

上调用虚拟方法'android.database.sqlite.SQLiteDatabase com.example.android.pets.data.petsdbhelper.getReadableDatabase（）'

但是我初始化了它！我该如何解决呢？

public class petProvider extends ContentProvider {

public static final String LOG_TAG = petProvider.class.getSimpleName();
 public petsdbhelper phelper = new petsdbhelper(getContext());

public final static UriMatcher uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);

static {
    uriMatcher.addURI(blankContract.content_authority,"pets",1);
    uriMatcher.addURI(blankContract.content_authority,"pets/#",2);
}

@Override
public boolean onCreate() {



    return true;
}

@Nullable
@Override
public Cursor query(@NonNull Uri uri, @Nullable String[] strings, @Nullable String s, @Nullable String[] strings1, @Nullable String s1) {

   SQLiteDatabase sql = phelper.getReadableDatabase();

   Cursor cursor = null ;

   int match = uriMatcher.match(uri);

   switch (match){
       case 1:
           cursor = sql.query(blankContract.blankEntry.TABLE_NAME , strings,s,strings1,null,null,s1);
           break;
       case 2:
            s = blankContract.blankEntry.COULUMN_ID +"=?";
            strings1 = new String[] { String.valueOf(ContentUris.parseId(uri))};
            cursor = sql.query(blankContract.blankEntry.TABLE_NAME,strings,s,strings1,null,null,s1);
            break;
       default:
           throw new IllegalArgumentException("cannot query unknown "+uri);
   }

    return cursor;
}