Question

所以...我一直在制作我自己的应用程序（它就像一个联系人应用程序，只是不同），这部分让我疯了！问题在于，无论何时调用getAllProfiles（）方法，它都不会返回任何行，即使在插入新行之后......我做错了什么？

这是帮助类的代码：

public class DBHelper extends SQLiteOpenHelper{

public static final String TABLE_NAME = "profiles";
public static final String COLUMN_ID = "id";
public static final String COLUMN_FNAME = "fname";
public static final String COLUMN_LNAME = "lname";
public static final String COLUMN_SORT = "id DESC";


public DBHelper(Context context, String name, CursorFactory factory, int version) {
    super(context, name, factory, version);
    // TODO Auto-generated constructor stub
}


@Override
public void onCreate(SQLiteDatabase db) {
    // When creating the DB from the start...
    db.execSQL("CREATE TABLE profiles(id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, fname TEXT, lname TEXT)");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // TODO Auto-generated method stub
    db.execSQL("DROP TABLE IF EXISTS contacts");
    onCreate(db);
}

public boolean insertProfile(Profile p) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues cv = new ContentValues();
    cv.put("fname", p.getFname());
    cv.put("lname", p.getLname());
    long ret = db.insert("profiles", null, cv);
    if(ret == -1){
        Log.d("INSFL", "Insertion Failed!");
    }

    return true;
}

public Cursor getSpecificProfile(int id){
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor res = db.rawQuery("SELECT * FROM profiles WHERE id="+id+"" , null);
    return res;
}

public int getNumOfProfiles(){
    SQLiteDatabase db = this.getReadableDatabase();
    int num = (int)DatabaseUtils.queryNumEntries(db, TABLE_NAME);
    return num;
}

public int deleteProfile(Profile p){
    SQLiteDatabase db = this.getWritableDatabase();
    return db.delete("profiles", "id = "+p.getId()+"", null);
}

public ArrayList<Profile> getAllProfiles(){
    ArrayList<Profile> profiles = new ArrayList<Profile>();

    SQLiteDatabase db = this.getReadableDatabase();
    String[] projection = {
        COLUMN_ID,
        COLUMN_FNAME,
        COLUMN_LNAME
    };
    Cursor res = db.query(TABLE_NAME, projection, null ,null,null,null,COLUMN_SORT);

    if(res.getCount() == 0){
        Log.d("No Column", "ERROR: NO ROWS RETURNED");
    }

    if(res.moveToFirst()){
        Log.d("BS", "Query Successful");
    }

    while (!(res.isAfterLast())){
        // CHANGE ACCORDINGLY WHEN UPDATING
        Profile p = new Profile();
        int id = res.getInt(0);
        String fname = res.getString(1);
        String lname = res.getString(2);

        p.setId(id);
        p.setFname(fname);
        p.setLname(lname);

        profiles.add(p);
        Log.d("BS", "Entry added successfully!");
    }


    return profiles;
}

}

Answer 1

你的while循环无限重复，因为你永远不会将光标移到第一行之外。它将使用第一行的数据创建相同的Profile个对象，并将它们添加到ArrayList，直到内存不足为止。

我更喜欢使用for循环语法迭代游标，即使使用空游标也会表现良好：

for (cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()) {
    // do something here
}

或者，在您的代码中，您只需要在cursor.moveToNext()行之后添加profiles.add(p)。

Android中的SQLite数据库返回零行

1 个答案: