空对象引用上的android.content.Context.getContentResolver()’
作者：互联网
我似乎无法解决为什么我得到一个空指针？
这是我调用的AsyncTask来获取数据.它将它传递给JSON Parser并返回一个Objects数组.然后将其传递给我的DBHelper,它通过ContentResolver传递给我的数据库….
public class getFilms extends AsyncTask<String, Void, Void> {
public int LIMIT_FILMS = 10;
String KEY = "apikey";
String LIMIT = "limit";
private static final String URL = "http://api.rottentomatoes.com/api/public/v1.0/lists/movies/box_office.json?";
private static final String API_KEY = "******************";
ArrayList<HashMap<String, String>> filmArrayList = new ArrayList<HashMap<String, String>>();
Context mContext;
@Override
protected Void doInBackground(String... params) {
Uri RottenUrl = Uri.parse(URL).buildUpon()
.appendQueryParameter(KEY, API_KEY)
.appendQueryParameter(LIMIT, Integer.toString(LIMIT_FILMS))
.build();
JSONParser jParser = new JSONParser();
Film[] json = jParser.getJSONFromUrl(RottenUrl.toString());
sortData(json);
return null;
}
public void sortData(Film[] jsonlist) {
DatabaseHelper dbHelper = new DatabaseHelper(mContext, null, null, 1);
dbHelper.deleteAll();
for (int i = 0; i < jsonlist.length; i++) {
dbHelper.contentAddFilm(jsonlist[i]);
}
}
}
这是我的数据库助手
public class DatabaseHelper extends SQLiteOpenHelper {
private ContentResolver myCR;
public DatabaseHelper(Context context, String name,
SQLiteDatabase.CursorFactory factory, int version) {
super(context, FilmDataContract.DATABASE_NAME, factory, FilmDataContract.DATABASE_VERSION);
myCR = context.getContentResolver();
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(FilmDataContract.FilmEntry.SQL_CREATE_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL(FilmDataContract.FilmEntry.DELETE_TABLE);
onCreate(db);
}
public void addFilm(Film film) {
ContentValues values = new ContentValues();
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_TITLE, film.getTitle());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_RATING, film.getRating());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_RUNTIME, film.getRuntime());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_CRITICS, film.getCritics());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_AUDIENCE, film.getAudience());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_SYNOPSIS, film.getSynopsis());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_PROFILE, film.getProfile());
SQLiteDatabase db = this.getWritableDatabase();
db.insert(FilmDataContract.TABLE_NAME,
null,
values);
db.close();
}
public Film getFilm(int id) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor =
db.query(FilmDataContract.TABLE_NAME,
FilmDataContract.FilmEntry.COLUMNS,
"_id = ?",
new String[]{String.valueOf(id)},
null,
null,
null,
null);
if (cursor != null)
cursor.moveToFirst();
Film film = new Film();
film.setTitle(cursor.getString(1));
film.setRating(cursor.getString(2));
film.setRuntime(cursor.getString(3));
film.setCritics(cursor.getString(4));
film.setAudience(cursor.getString(5));
film.setSynopsis(cursor.getString(6));
film.setProfile(cursor.getString(7));
return film;
}
public List<Film> getAllFilms() {
List<Film> films = new LinkedList<Film>();
String query = "SELECT * FROM " + FilmDataContract.TABLE_NAME;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(query, null);
Film film = null;
if (cursor.moveToFirst()) {
do {
film = new Film();
film.setId(Integer.parseInt(cursor.getString(0)));
film.setTitle(cursor.getString(1));
film.setRating(cursor.getString(2));
film.setRuntime(cursor.getString(3));
film.setCritics(cursor.getString(4));
film.setAudience(cursor.getString(5));
film.setSynopsis(cursor.getString(6));
film.setProfile(cursor.getString(7));
films.add(film);
} while (cursor.moveToNext());
}
return films;
}
public int updateFilm(Film film) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_TITLE, film.getTitle());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_RATING, film.getRating());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_RUNTIME, film.getRuntime());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_CRITICS, film.getCritics());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_AUDIENCE, film.getAudience());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_SYNOPSIS, film.getSynopsis());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_PROFILE, film.getProfile());
int i = db.update(FilmDataContract.FilmEntry.TABLE_NAME,
values,
"_id+ = ?",
new String[]{String.valueOf(film.getId())});
db.close();
return i;
}
public int getFilmsCount() {
String countQuery = "SELECT * FROM " + FilmDataContract.FilmEntry.TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
int cnt = cursor.getCount();
cursor.close();
return cnt;
}
public void deleteAll() {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(FilmDataContract.FilmEntry.TABLE_NAME, null, null);
}
public boolean contentDelete(String filmName) {
boolean result = false;
String selection = "title = \"" + filmName + "\"";
int rowsDeleted = myCR.delete(FilmProvider.CONTENT_URI,
selection, null);
if (rowsDeleted > 0)
result = true;
return result;
}
public Film contentFindFilm(String filmName) {
String[] projection = FilmDataContract.FilmEntry.COLUMNS;
String selection = "title = \"" + filmName + "\"";
Cursor cursor = myCR.query(FilmProvider.CONTENT_URI,
projection, selection, null,
null);
Film film = new Film();
if (cursor.moveToFirst()) {
cursor.moveToFirst();
film.setId(Integer.parseInt(cursor.getString(0)));
film.setTitle(cursor.getString(1));
film.setRating(cursor.getString(2));
film.setRuntime(cursor.getString(3));
film.setCritics(cursor.getString(4));
film.setAudience(cursor.getString(5));
film.setSynopsis(cursor.getString(6));
film.setProfile(cursor.getString(7));
cursor.close();
} else {
film = null;
}
return film;
}
public void contentAddFilm(Film film) {
ContentValues values = new ContentValues();
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_TITLE, film.getTitle());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_RATING, film.getRating());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_RUNTIME, film.getRuntime());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_CRITICS, film.getCritics());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_AUDIENCE, film.getAudience());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_SYNOPSIS, film.getSynopsis());
values.put(FilmDataContract.FilmEntry.COLUMN_FILM_PROFILE, film.getProfile());
myCR.insert(FilmProvider.CONTENT_URI, values);
}
这是我的堆栈跟踪……当我传递上下文时似乎正在发生.
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.ContentResolver android.content.Context.getContentResolver()' on a null object reference
at com.purewowstudio.topmovies.data.DatabaseHelper.<init>(DatabaseHelper.java:25)
at com.purewowstudio.topmovies.util.getFilms.sortData(getFilms.java:48)
at com.purewowstudio.topmovies.util.getFilms.doInBackground(getFilms.java:43)
at com.purewowstudio.topmovies.util.getFilms.doInBackground(getFilms.java:16)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
在android.os.AsyncTask $SerialExecutor $1.run(AsyncTask.java:231)
解决方法:
DatabaseHelper dbHelper = new DatabaseHelper(mContext, null, null, 1);
mContext为null,因为您从不为其赋值.
标签：android,android-context,android-asynctask,android-activity 来源： https://codeday.me/bug/20191009/1875662.html