因此,我在 MainActivity
中定义了一个 SQLiteDatabase
,我使用一些文本框和一个确认输入的按钮填充它。这是定义:
public class MainActivity extends AppCompatActivity {
SQLiteDatabase clientsDatabase;
...
稍后,在我的 MainActivity
的 OnCreate
中,我尝试使用这段代码来设置数据库:
clientsDatabase = this.openOrCreateDatabase("Clients", MODE_PRIVATE, null);
clientsDatabase.execSQL("CREATE TABLE IF NOT EXISTS clients (id INT(3), fName VARCHAR, lName VARCHAR, age INT(3))");
我有一个将数据放入数据库的函数:
clientsDatabase.execSQL("INSERT INTO clients (id, fName, lName, age) VALUES (" + id + ", '" + f + "', '" + l + "', " + a + ")");
我有一个 ListView
,我使用该数据库中的数据填写了它。我想将此 ListView
移动到另一个 Activity 。我如何使这个数据库成为可以在我的应用程序中的任何 Activity 中访问和编辑的全局事物?我的应用程序中几乎每个 Activity 都需要与数据库交互,那么我有哪些选择?
最佳答案
只需添加名为“DatabaseHandler”的新 java 类并将下面的代码 fragment 粘贴到您的新 java 文件中。
public class DatabaseHandler extends SQLiteOpenHelper {
// All Static variables
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "your database name";
// Contacts table name
private static final String TABLE_CONTACTS = "your table name";
// 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) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);
// Create tables again
onCreate(db);
}
/**
* All CRUD(Create, Read, Update, Delete) Operations
*/
// Adding new contact
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
// Inserting Row
db.insert(TABLE_CONTACTS, null, values);
db.close(); // Closing database connection
}
// Getting single contact
Contact getContact(int id) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
KEY_NAME, KEY_PH_NO }, KEY_ID + "=?",
new String[] { String.valueOf(id) }, null, null, null, null);
if (cursor != null)
cursor.moveToFirst();
Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
cursor.getString(1), cursor.getString(2));
// return contact
return contact;
}
// 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));
// 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();
}
}
现在,如果您想要所有这些方法,只需在您的 Activity 中初始化“DatabaseHandler”,如下所示。
DatabaseHandler DBHelper = new DatabaseHandler(getApplicationContext());
要访问任何方法,只需像下面这样写。
DBHepler.addContact(your object);
关于android - Android Studio 中的全局 SQLite 数据库,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41050859/