我目前正在学习使用SQLite存储一些数据。当前项目计划成为Notes应用程序。启动应用程序时，会出现许多错误。一个是它不能插入数据，另一个是表注释不存在。如果我保留代码以在登录名中显示数据，则该应用程序将崩溃。
我试图删除该函数以检索数据并显示它，并且应用程序停止崩溃，但是，我仍然遇到无法将数据插入表的错误
wxPythonprotected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DatabaseHandler db = new DatabaseHandler(this);
db.AddNote(new Note("12313", "jkfsabk"));
List<Note> notes = db.getAllNotes();
for (Note c: notes){
String log = "NAME: " + c.getNoteName() + " DESCRIPTION: " + c.getNoteDescription() + "\n";
text = text + log;
}
System.out.println(text);
public class DatabaseHandler extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "notesDB";
private static final String TABLE_NAME = "notes";
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_DESCRIPTION = "description";
public DatabaseHandler(Context context) {
super(context, Util.DATABASE_NAME, null, Util.DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_CONTACT_TABLE = "CREATE TABLE " + TABLE_NAME + "(" + KEY_ID + " INTEGER PRIMARY KEY ," + KEY_NAME + " TEXT," + KEY_DESCRIPTION + " TEXT)";
db.execSQL(CREATE_CONTACT_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
public void AddNote(Note note){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues value = new ContentValues();
value.put(KEY_NAME, note.getNoteName());
value.put(KEY_DESCRIPTION, note.getNoteDescription());
db.insert(TABLE_NAME, null, value);
db.close();
}
Note getNote(int id) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(TABLE_NAME, new String[]{KEY_ID, KEY_NAME, KEY_DESCRIPTION}, KEY_ID
+ "=?", new String[]{String.valueOf(id)}, null, null, null, null);
if (cursor != null){
cursor.moveToFirst();
}
Note note = new Note(Integer.parseInt(cursor.getString(0)), cursor.getString(1), cursor.getString(2));
return note;
}
public List<Note> getAllNotes(){
List<Note> noteList = new ArrayList<>();
String selectQuery = "SELECT * FROM " + TABLE_NAME;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
if(cursor.moveToFirst()){
do{
Note note = new Note();
note.setID(Integer.parseInt(cursor.getString(0)));
note.setNoteName(cursor.getString(1));
note.setNoteDescription(cursor.getString(2));
noteList.add(note);
} while(cursor.moveToNext());
} cursor.close();
return noteList;
}
public int updateNotes(Note note){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, note.getNoteName());
values.put(KEY_DESCRIPTION, note.getNoteDescription());
return db.update(TABLE_NAME, values, KEY_ID + "=?", new String[]{String.valueOf(note.getID())});
}
public void deleteNote(Note note){
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_NAME, KEY_ID + "=?", new String[]{String.valueOf(note.getID())});
db.close();
}
public int getNoteCount(Note note){
String countQuery = "SELECT * FROM " + TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
cursor.close();
return cursor.getCount();
}
}
我希望输出
名称：12313说明：jkfsabk，
但是我得到了错误：
public class Note {
private int noteID;
private String noteName;
private String noteDescription;
public Note() {}
public Note(Integer id, String notename, String notedescription) {
this.noteID = id;
this.noteName = notename;
this.noteDescription = notedescription;
}
public Note(String notename, String notedescription){
this.noteName = notename;
this.noteDescription = notedescription;
}
public void setID(int id) {
this.noteID = id;
}
public int getID() {
return this.noteID;
}
public void setNoteName(String notename) {
this.noteName = notename;
}
public String getNoteName() {
return this.noteName;
}
public void setNoteDescription(String notedescription) {
this.noteDescription = notedescription;
}
public String getNoteDescription() {
return this.noteDescription;
}
}
答案 0 :(得分：0)
我在您的代码中进行了一些更正，尝试了此代码，然后得到您想要的结果。试试吧。
1- DatabaseHandler类
public class DatabaseHandler extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "notesDB";
private static final String TABLE_NAME = "notes";
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_DESCRIPTION = "description";
public DatabaseHandler(Context context) {
super(context, DATABASE_NAME , null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_CONTACT_TABLE = "CREATE TABLE " + TABLE_NAME + "(" + KEY_ID + " INTEGER PRIMARY KEY ," + KEY_NAME + " TEXT," + KEY_DESCRIPTION + " TEXT)";
db.execSQL(CREATE_CONTACT_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
public void AddNote(Note note){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues value = new ContentValues();
value.put(KEY_NAME, note.getNoteName());
value.put(KEY_DESCRIPTION, note.getNoteDescription());
db.insert(TABLE_NAME, null, value);
db.close();
}
Note getNote(int id) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(TABLE_NAME, new String[]{KEY_ID, KEY_NAME, KEY_DESCRIPTION}, KEY_ID
+ "=?", new String[]{String.valueOf(id)}, null, null, null, null);
if (cursor != null){
cursor.moveToFirst();
}
Note note = new Note(Integer.parseInt(cursor.getString(0)), cursor.getString(1), cursor.getString(2));
return note;
}
public ArrayList<Note> getAllNotes(){
ArrayList<Note> noteList = new ArrayList<>();
String selectQuery = "SELECT * FROM " + TABLE_NAME;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
if(cursor.moveToFirst()){
do{
Note note = new Note();
note.setID(Integer.parseInt(cursor.getString(0)));
note.setNoteName(cursor.getString(1));
note.setNoteDescription(cursor.getString(2));
noteList.add(note);
} while(cursor.moveToNext());
} cursor.close();
return noteList;
}
public int updateNotes(Note note){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, note.getNoteName());
values.put(KEY_DESCRIPTION, note.getNoteDescription());
return db.update(TABLE_NAME, values, KEY_ID + "=?", new String[]{String.valueOf(note.getID())});
}
public void deleteNote(Note note){
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_NAME, KEY_ID + "=?", new String[]{String.valueOf(note.getID())});
db.close();
}
public int getNoteCount(Note note){
String countQuery = "SELECT * FROM " + TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
cursor.close();
return cursor.getCount();
}
}
2- MainActivity类
setContentView(R.layout.activity_main);
DatabaseHandler db = new DatabaseHandler(this);
db.AddNote(new Note("12313", "jkfsabk"));
ArrayList<Note> notes = db.getAllNotes();
String log = null;
for (Note c: notes){
log = "NAME: " + c.getNoteName() + " DESCRIPTION: " + c.getNoteDescription() + "\n";
// text = text + log;
}
Toast.makeText(this, log+"" , Toast.LENGTH_SHORT).show();