📅  最后修改于: 2020-09-30 06:26:21             🧑  作者: Mango
SQLite是一个开放源代码的关系数据库,即用于在android设备上执行数据库操作,例如从数据库中存储,操作或检索持久性数据。
默认情况下,它嵌入在android中。因此,无需执行任何数据库设置或管理任务。
在这里,我们将看到sqlite存储和获取数据的示例。数据显示在logcat中。要在微调器或列表视图上显示数据,请移至下一页。
SQLiteOpenHelper类提供使用SQLite数据库的功能。
android.database.sqlite.SQLiteOpenHelper类用于数据库创建和版本管理。为了执行任何数据库操作,您必须提供SQLiteOpenHelper类的onCreate()和onUpgrade()方法的实现。
SQLiteOpenHelper类有两个构造函数。
Constructor | Description |
---|---|
SQLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) | creates an object for creating, opening and managing the database. |
SQLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version, DatabaseErrorHandler errorHandler) | creates an object for creating, opening and managing the database. It specifies the error handler. |
SQLiteOpenHelper类中有许多方法。其中一些如下:
Method | Description |
---|---|
public abstract void onCreate(SQLiteDatabase db) | called only once when database is created for the first time. |
public abstract void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) | called when database needs to be upgraded. |
public synchronized void close () | closes the database object. |
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) | called when database needs to be downgraded. |
它包含要在sqlite数据库上执行的方法,例如创建,更新,删除,选择等。
SQLiteDatabase类中有许多方法。其中一些如下:
Method | Description |
---|---|
void execSQL(String sql) | executes the sql query not select query. |
long insert(String table, String nullColumnHack, ContentValues values) | inserts a record on the database. The table specifies the table name, nullColumnHack doesn’t allow completely null values. If second argument is null, android will store null values if values are empty. The third argument specifies the values to be stored. |
int update(String table, ContentValues values, String whereClause, String[] whereArgs) | updates a row. |
Cursor query(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy) | returns a cursor over the resultset. |
让我们看看android sqlite数据库的简单示例。
package example.javatpoint.com.sqlitetutorial;
public class Contact {
int _id;
String _name;
String _phone_number;
public Contact(){ }
public Contact(int id, String name, String _phone_number){
this._id = id;
this._name = name;
this._phone_number = _phone_number;
}
public Contact(String name, String _phone_number){
this._name = name;
this._phone_number = _phone_number;
}
public int getID(){
return this._id;
}
public void setID(int id){
this._id = id;
}
public String getName(){
return this._name;
}
public void setName(String name){
this._name = name;
}
public String getPhoneNumber(){
return this._phone_number;
}
public void setPhoneNumber(String phone_number){
this._phone_number = phone_number;
}
}
现在,让我们创建扩展SQLiteOpenHelper类并提供其方法实现的数据库处理程序类。
package example.javatpoint.com.sqlitetutorial;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.util.ArrayList;
import java.util.List;
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";
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);
//3rd argument to be passed is CursorFactory instance
}
// 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);
}
// code to add the 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);
//2nd argument is String containing nullColumnHack
db.close(); // Closing database connection
}
// code to get the 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;
}
// code to get all contacts in a list view
public List getAllContacts() {
List contactList = new ArrayList();
// 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;
}
// code to update the 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();
}
}
package example.javatpoint.com.sqlitetutorial;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import java.util.List;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DatabaseHandler db = new DatabaseHandler(this);
// Inserting Contacts
Log.d("Insert: ", "Inserting ..");
db.addContact(new Contact("Ravi", "9100000000"));
db.addContact(new Contact("Srinivas", "9199999999"));
db.addContact(new Contact("Tommy", "9522222222"));
db.addContact(new Contact("Karthik", "9533333333"));
// Reading all contacts
Log.d("Reading: ", "Reading all contacts..");
List 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);
}
}
}
请按照以下步骤查看数据库及其存储在android sqlite中的数据: