这是笔记应用编码的主页：
public class Note_mainActivity extends Fragment implements NoteRecyclerAdapter.NoteOnClick,LoaderManager.LoaderCallbacks<Cursor>{
private RecyclerView mRecycler8;
private NoteRecyclerAdapter mAdapter8;
private List savedNote;
private MyDbHelper myDbHelper;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View rootView1 = inflater.inflate(R.layout.activity_note_main,container,false);
savedNote = new ArrayList<>();
mRecycler8 = (RecyclerView)rootView1.findViewById(R.id.show_note);
WrappedLinearLayoutManager linearLayoutManager = new WrappedLinearLayoutManager(getActivity());
mRecycler8.setLayoutManager(linearLayoutManager);
mAdapter8 = new NoteRecyclerAdapter(getActivity(),this);
mRecycler8.setItemAnimator(new SlideInDownAnimator());
mRecycler8.setHasFixedSize(true);
mAdapter8.setData(savedNote);
myDbHelper = new MyDbHelper(getActivity());
getActivity().getSupportLoaderManager().initLoader(0,null,this);
getActivity().getSupportLoaderManager().initLoader(1,null,this);
return rootView1;
}
@Override
public void containerOnClick(int t) {
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
if(id==0){
return new CursorLoader(getActivity(), NoteContract.NoteItemRow.CONTENT_URI,null,null,null,null);
}else{
return new CursorLoader(getActivity(), NoteContract.NoteItemRow.CONTENT_URI_NEWS,null,null,null,null);
}
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
if(loader.getId() ==0){
if(data.moveToFirst()){
do{
int title1 = data.getColumnIndex(NoteContract.NoteItemRow.NOTE);
int date1 = data.getColumnIndex(NoteContract.NoteItemRow.DATE);
String title2 = data.getString(title1);
String date2 = data.getString(date1);
Notesetter setter1 = new Notesetter(title2,date2);
savedNote.add(setter1);
mAdapter8.notifyDataSetChanged();
}while(data.moveToNext());
}
}else{
/* if(data.moveToFirst()){
do{
int title2 = data.getColumnIndex(NoteContract.NoteItemRow.NEWS_TITLE);
int image_url = data.getColumnIndex(NoteContract.NoteItemRow.NEWS_IMAGE);
int source_url = data.getColumnIndex(NoteContract.NoteItemRow.NEWS_URL);
int date3 = data.getColumnIndex(NoteContract.NoteItemRow.NEWS_DATE);
String title3 = data.getString(title2);
String image_url_3 = data.getString(image_url);
String sources_url3 =data.getString(source_url);
String date_saved3 = data.getString(date3);
NewsNotesetter setter1 = new NewsNotesetter(title3,image_url_3,sources_url3,date_saved3);
savedNote.add(setter1);
mAdapter8.notifyDataSetChanged();
}while(data.moveToNext());
}*/
}
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
}
}
是我的内容提供商编码：
public class TheNewProvider extends ContentProvider {
private MyDbHelper myDbHelper;
private static final String LOG_TAG = TheNewProvider.class.getSimpleName();
private static final int SIMPLE_NOTE =100;
private static final int SIMPLE_NOTE_ID=101;
private static final int NEWS_NOTE =102;
private static final int NEWS_NOTE_ID =103;
private static final UriMatcher sUriMAtcher = new UriMatcher(UriMatcher.NO_MATCH);
static{
sUriMAtcher.addURI(NoteContract.CONTENT_AUTHORITY, NoteContract.path_note,SIMPLE_NOTE);
sUriMAtcher.addURI(NoteContract.CONTENT_AUTHORITY, NoteContract.path_note+"/#",SIMPLE_NOTE_ID);
sUriMAtcher.addURI(NoteContract.CONTENT_AUTHORITY, NoteContract.path_news,NEWS_NOTE);
sUriMAtcher.addURI(NoteContract.CONTENT_AUTHORITY, NoteContract.path_news+"/#",NEWS_NOTE_ID);
}
@Override
public boolean onCreate() {
myDbHelper = new MyDbHelper(getContext());
return true;
}
@Nullable
@Override
public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
SQLiteDatabase sqLiteDatabase = myDbHelper.getReadableDatabase();
Cursor cursor;
int match = sUriMAtcher.match(uri);
switch (match){
case SIMPLE_NOTE:
cursor = sqLiteDatabase.query(NoteContract.NoteItemRow.TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder);
break;
case SIMPLE_NOTE_ID:
selection = NoteContract.NoteItemRow._ID+"=?";
selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
cursor = sqLiteDatabase.query(NoteContract.NoteItemRow.TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder);
break;
case NEWS_NOTE:
cursor = sqLiteDatabase.query(NoteContract.NoteItemRow.TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder);
break;
case NEWS_NOTE_ID:
selection = NoteContract.NoteItemRow._ID+"=?";
selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
cursor = sqLiteDatabase.query(NoteContract.NoteItemRow.TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder);
break;
default:
throw new IllegalArgumentException("Insertion is not supported" +uri);
}
cursor.setNotificationUri(getContext().getContentResolver(), NoteContract.NoteItemRow.CONTENT_URI);
cursor.setNotificationUri(getContext().getContentResolver(), NoteContract.NoteItemRow.CONTENT_URI_NEWS);
return cursor;
}
@Nullable
@Override
public String getType(@NonNull Uri uri) {
return null;
}
@Nullable
@Override
public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
final int match = sUriMAtcher.match(uri);
switch (match){
case SIMPLE_NOTE:
return save(uri,values);
case NEWS_NOTE:
return saveNews(uri,values);
default:
throw new IllegalArgumentException("Insertion is not supported" +uri);
}
}
@Override
public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
return 0;
}
@Override
public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
final int match = sUriMAtcher.match(uri);
switch (match){
case SIMPLE_NOTE:
return UpdateNote(uri,values,selection,selectionArgs);
case SIMPLE_NOTE_ID:
selection = NoteContract.NoteItemRow._ID+"=?";
selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
return UpdateNote(uri,values,selection,selectionArgs);
case NEWS_NOTE:
return UpdateNews(uri,values,selection,selectionArgs);
case NEWS_NOTE_ID:
selection = NoteContract.NoteItemRow._ID+"=?";
selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};
return UpdateNews(uri,values,selection,selectionArgs);
default:
throw new IllegalArgumentException("Insertion is not supported" +uri);
}
}
private Uri save(Uri url,ContentValues values){
String name = values.getAsString(NoteContract.NoteItemRow.TITLE);
if(name == null){
throw new IllegalArgumentException("no title");
}
String notes = values.getAsString(NoteContract.NoteItemRow.NOTE);
if(notes == null){
throw new IllegalArgumentException("no note");
}
String date = values.getAsString(NoteContract.NoteItemRow.DATE);
if(date == null){
throw new IllegalArgumentException("no date");
}
SQLiteDatabase db = myDbHelper.getWritableDatabase();
long id = db.insert(NoteContract.NoteItemRow.TABLE_NAME,null,values);
if(id==-1){
Log.v("the note","saved");
}
getContext().getContentResolver().notifyChange(url,null);
return ContentUris.withAppendedId(url,id);
}
private Uri saveNews(Uri url,ContentValues values){
String name = values.getAsString(NoteContract.NoteItemRow.NEWS_TITLE);
if(name == null){
throw new IllegalArgumentException("no title");
}
String notes = values.getAsString(NoteContract.NoteItemRow.NEWS_URL);
if(notes == null){
throw new IllegalArgumentException("no note");
}
String date = values.getAsString(NoteContract.NoteItemRow.NEWS_DATE);
if(date == null){
throw new IllegalArgumentException("no date");
}
String image_url = values.getAsString(NoteContract.NoteItemRow.NEWS_IMAGE);
if(image_url == null){
throw new IllegalArgumentException("no image");
}
SQLiteDatabase db = myDbHelper.getWritableDatabase();
long id = db.insert(NoteContract.NoteItemRow.TABLE_NAME,null,values);
if(id==-1){
Log.v("the note","saved");
}
getContext().getContentResolver().notifyChange(url,null);
return ContentUris.withAppendedId(url,id);
}
private int UpdateNote(Uri url,ContentValues values,String selection,String[]selectionArgs){
String name = values.getAsString(NoteContract.NoteItemRow.TITLE);
if(name == null){
throw new IllegalArgumentException("no title");
}
String notes = values.getAsString(NoteContract.NoteItemRow.NOTE);
if(notes == null){
throw new IllegalArgumentException("no note");
}
String date = values.getAsString(NoteContract.NoteItemRow.DATE);
if(date == null){
throw new IllegalArgumentException("no date");
}
SQLiteDatabase db = myDbHelper.getWritableDatabase();
int rowUpdated = db.update(NoteContract.NoteItemRow.TABLE_NAME,values,selection,selectionArgs);
if(rowUpdated!=0){
getContext().getContentResolver().notifyChange(url,null);
}
return rowUpdated;
}
private int UpdateNews(Uri url,ContentValues values,String selection,String[]selectionArgs){
String name = values.getAsString(NoteContract.NoteItemRow.NEWS_TITLE);
if(name == null){
throw new IllegalArgumentException("no title");
}
String notes = values.getAsString(NoteContract.NoteItemRow.NEWS_URL);
if(notes == null){
throw new IllegalArgumentException("no note");
}
String date = values.getAsString(NoteContract.NoteItemRow.NEWS_DATE);
if(date == null){
throw new IllegalArgumentException("no date");
}
String image_url = values.getAsString(NoteContract.NoteItemRow.NEWS_IMAGE);
if(image_url == null){
throw new IllegalArgumentException("no image");
}
SQLiteDatabase db = myDbHelper.getWritableDatabase();
int rowUpdated = db.update(NoteContract.NoteItemRow.TABLE_NAME,values,selection,selectionArgs);
if(rowUpdated!=0){
getContext().getContentResolver().notifyChange(url,null);
}
return rowUpdated;
}
}
这是我的databasehelper类：
public class MyDbHelper extends SQLiteOpenHelper {
private static final int DATABSE_VERSION = 1;
private static final String DATABASE_NAME ="simpleTable.db";
private static final String createDatabase = "CREATE TABLE "
+ NoteItemRow.TABLE_NAME
+"("+NoteItemRow._ID+" INTEGER PRIMARY KEY AUTOINCREMENT, "
+NoteItemRow.TITLE+" TEXT, "
+NoteItemRow.NOTE+" TEXT NOT NULL, "
+NoteItemRow.DATE+" TEXT NOT NULL);";
private static final String createDatabase2 = "CREATE TABLE "
+ NoteItemRow.TABLE_NAME2
+"("+NoteItemRow._ID+" INTEGER PRIMARY KEY AUTOINCREMENT, "
+NoteItemRow.NEWS_TITLE+" TEXT, "
+NoteItemRow.NEWS_URL+" TEXT NOT NULL, "
+NoteItemRow.NEWS_DATE+" TEXT NOT NULL, "
+NoteItemRow.NEWS_IMAGE+" TEXT NOT NULL);";
private static final String UPGRADE_DB = "DROP TABLE IF EXISTS"+ NoteItemRow.TABLE_NAME;
private static final String UPGRADE_DB2 = "DROP TABLE IF EXISTS"+ NoteItemRow.TABLE_NAME2;
public MyDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABSE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(createDatabase);
db.execSQL(createDatabase2);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL(UPGRADE_DB);
db.execSQL(UPGRADE_DB2);
onCreate(db);
}
} 这是我的编辑课：
public class EditActivity extends AppCompatActivity {
private EditText mTitle,mNote;
String title1;
String note_detail;
private MyDbHelper mDbHelper;
private Uri cureenturi;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.note_editor);
mTitle = (EditText)findViewById(R.id.title_note);
mNote = (EditText)findViewById(R.id.take_note);
}
private void savenote(){
title1 = mTitle.getText().toString().trim();
note_detail = mNote.getText().toString().trim();
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yy");
Date date = new Date();
String date_cur = sdf.format(date);
mDbHelper = new MyDbHelper(this);
ContentValues values = new ContentValues();
values.put(NoteContract.NoteItemRow.TITLE,title1);
values.put(NoteContract.NoteItemRow.NOTE,note_detail);
values.put(NoteContract.NoteItemRow.DATE,date_cur);
cureenturi = getContentResolver().insert(NoteContract.NoteItemRow.CONTENT_URI,values);
if(cureenturi == null){
return;
}else {
int updateRow = getContentResolver().update(cureenturi,values,null,null);
if(updateRow==0){
}else {
Toast.makeText(EditActivity.this,"note updated",Toast.LENGTH_SHORT).show();
}
}
Uri newUriContent = getContentResolver().insert(NoteContract.NoteItemRow.CONTENT_URI,values);
if(newUriContent==null){
Toast.makeText(EditActivity.this,"can't created the note",Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(EditActivity.this,"note inserted",Toast.LENGTH_SHORT).show();
}
}
@Override
public void onBackPressed() {
super.onBackPressed();
if(TextUtils.isEmpty(title1)&&TextUtils.isEmpty(note_detail)){
finish();
}else{
savenote();
}
}
当我启动应用程序时，错误日志显示此错误：
Process: com.example.user.inforting, PID: 5490
java.lang.NullPointerException: Attempt to invoke interface method 'boolean android.database.Cursor.moveToFirst()' on a null object reference
at com.example.user.inforting.Note_mainActivity.onLoadFinished(Note_mainActivity.java:72)
at com.example.user.inforting.Note_mainActivity.onLoadFinished(Note_mainActivity.java:30)
at android.support.v4.app.LoaderManagerImpl$LoaderInfo.callOnLoadFinished(LoaderManager.java:476)
at android.support.v4.app.LoaderManagerImpl$LoaderInfo.onLoadComplete(LoaderManager.java:444)
at android.support.v4.content.Loader.deliverResult(Loader.java:126)
at android.support.v4.content.CursorLoader.deliverResult(CursorLoader.java:105)
at android.support.v4.content.CursorLoader.deliverResult(CursorLoader.java:37)
at android.support.v4.content.AsyncTaskLoader.dispatchOnLoadComplete(AsyncTaskLoader.java:252)
at android.support.v4.content.AsyncTaskLoader$LoadTask.onPostExecute(AsyncTaskLoader.java:80)
at android.support.v4.content.ModernAsyncTask.finish(ModernAsyncTask.java:485)
at android.support.v4.content.ModernAsyncTask$InternalHandler.handleMessage(ModernAsyncTask.java:502)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
答案 0 :(得分：0)
正如我看到的程序错误日志所示：
对空对象引用'boolean android.database.Cursor.moveToFirst（）'
还有 MoveToFirst 方法，将光标移动到第一行。
因此，根据我的意见，您尚未启动SQLiteDataBase，或者您通过程序丢失了DataBase的引用对象。
希望它会有所帮助。