📜  Android SQLite教程

📅  最后修改于: 2020-09-30 06:26:21             🧑  作者: Mango

Android SQLite教程

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。

SQLiteOpenHelper类

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类的构造方法

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类的方法

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.

SQLiteDatabase类

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类的方法

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.

Android SQLite数据库示例

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);
        }
    }
}

输出:

如何在Android Studio中查看存储在sqlite中的数据?

请按照以下步骤查看数据库及其存储在android sqlite中的数据:

  • 打开文件资源管理器。
  • 转到数据目录内的数据目录。
  • 搜索您的应用程序包名称。
  • 在应用程序包内,转到将在其中找到数据库的数据库(contactsManager)。
  • 将数据库(contactsManager)保存到您喜欢的任何位置。
  • 下载任何SqLite浏览器插件或工具(在我的情况下为SQLite的DB Browser)。
  • 启动用于SQLite的数据库浏览器并打开数据库(contactsManager)。
  • 转到浏览数据->选择表(联系人),您将看到存储的数据。