Question

我使用以下代码显示数据库中的列表视图，但在列表中数据将重复显示。继承人的代码

public class MainActivity extends Activity {
private ListView gridView;
public static ArrayList<String> ArrayofName = new ArrayList<String>();

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    DatabaseHandler db = new DatabaseHandler(this);

    /**
     * CRUD Operations
     * */
    // Inserting Contacts
    Log.d("Insert: ", "Inserting ..");
    db.addContact(new Contact("Ravi", "91"));
    db.addContact(new Contact("Srinivas", "99"));
    db.addContact(new Contact("Tommy", "95"));
    db.addContact(new Contact("Karthik", "93"));

    // Reading all contacts
    Log.d("Reading: ", "Reading all contacts..");
    List<Contact> contacts = db.getAllContacts();

    for (Contact cn : contacts) {
        String log = "Id: " + cn.getID() + " ,Name: " + cn.getName()
                + " ,Phone: " + cn.getPhoneNumber();
        // Writing Contacts to log
        Log.d("Name: ", log);

    }

    db.getAllContacts();

    gridView = (ListView) findViewById(R.id.gridView1);

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, ArrayofName);

    gridView.setAdapter(adapter);

    gridView.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View v,
                int position, long id) {
            Toast.makeText(getApplicationContext(),
                    ((TextView) v).getText(), Toast.LENGTH_SHORT).show();
        }
    });
}
    }

Heres是另一个班级

public class DatabaseHandler extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "contactsManager";
private static final String TABLE_CONTACTS = "contacts";

// Contacts Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_PH_NO = "phone_number";

public DatabaseHandler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
            + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
            + KEY_PH_NO + " TEXT" + ")";
    db.execSQL(CREATE_CONTACTS_TABLE);
}

// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);
    onCreate(db);
}

void addContact(Contact contact) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(KEY_NAME, contact.getName()); // Contact Name
    values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone
    db.insert(TABLE_CONTACTS, null, values);
    db.close(); // Closing database connection
}

// Getting All Contacts
public List<Contact> getAllContacts() {
    List<Contact> contactList = new ArrayList<Contact>();
    // Select All Query
    String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS;

    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);

    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {
            Contact contact = new Contact();
            contact.setID(Integer.parseInt(cursor.getString(0)));
            contact.setName(cursor.getString(1));
            contact.setPhoneNumber(cursor.getString(2));

            String name = cursor.getString(1) + "\n" + cursor.getString(2);
            MainActivity.ArrayofName.add(name);
            // Adding contact to list
            contactList.add(contact);
        } while (cursor.moveToNext());
    }

    // return contact list
    return contactList;
}

// Updating single contact
public int updateContact(Contact contact) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_NAME, contact.getName());
    values.put(KEY_PH_NO, contact.getPhoneNumber());

    // updating row
    return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
            new String[] { String.valueOf(contact.getID()) });
}

// Deleting single contact
public void deleteContact(Contact contact) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
            new String[] { String.valueOf(contact.getID()) });
    db.close();
}

// Getting contacts Count
public int getContactsCount() {
    String countQuery = "SELECT  * FROM " + TABLE_CONTACTS;
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(countQuery, null);
    cursor.close();

    // return count
    return cursor.getCount();
}

    }

请告诉我数据重复的原因。正如您所看到的，只添加了四个联系人，但该列表显示了大约40个联系人，其中包含这四个联系人。

Answer 1

因为每次运行此应用程序时，您每次都会插入值。这就是为什么要获得重复值。因此，在向数据库插入值之前，请清除数据库或使用共享首选项，并在第一次运行时将数据插入数据库。

Answer 2

在您的代码中进行以下更改：

在Databasehandler.java中：使返回类型无效＆amp;相应地改变函数getAllContacts（）

在MainActivity.java中：评论以下部分..：

// Reading all contacts
Log.d("Reading: ", "Reading all contacts..");
List<Contact> contacts = db.getAllContacts();

for (Contact cn : contacts) {
    String log = "Id: " + cn.getID() + " ,Name: " + cn.getName()
            + " ,Phone: " + cn.getPhoneNumber();
    // Writing Contacts to log
    Log.d("Name: ", log);

}

数据在列表中重复出现

2 个答案: