数据库

简单应用

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHelper extends SQLiteOpenHelper{
    // 带全部参数的构造函数，此构造函数必不可少
    public DatabaseHelper(Context context, String name, CursorFactory factory, int version) {
        super(context, name, factory, version);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        // 创建数据库sql语句 并 执行
        String sql = "create table user(name varchar(20))";
        db.execSQL(sql);
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // 版本变化时调用
    }
}
// -------- 应用 --------
//依靠DatabaseHelper的构造函数创建数据库
DatabaseHelper dbHelper = new DatabaseHelper(MainActivity.this, "test_db", null, 1);
db = dbHelper.getWritableDatabase();

// -- 插入 --
db.insert("user", null, values);

// -- 删除 --
db.delete("user", "name=?", new String[]{deleteData});

// -- 更新 --
db.update("user", values2, "name = ?", new String[]{beforeUpdateData});

// -- 查询 --
// 创建游标对象
Cursor cursor = db.query("user", new String[]{"name"}, null, null, null, null, null);
// 利用游标遍历所有数据对象
while (cursor.moveToNext()) {
    String name = cursor.getString(cursor.getColumnIndex("name"));
}

加密

// https://github.com/sqlcipher/android-database-sqlcipher
implementation "net.zetetic:android-database-sqlcipher:4.3.0@aar"
implementation "androidx.sqlite:sqlite:2.1.0"

// 补充全局初始化
SQLiteDatabase.loadLibs(this);

// 替换导入
import net.sqlcipher.Cursor;
import net.sqlcipher.database.SQLiteDatabase;
import net.sqlcipher.database.SQLiteOpenHelper;

// 数据库操作句柄
public SQLiteDatabase reader() {
    return this.getReadableDatabase("test");
}

public SQLiteDatabase writer() {
    return this.getWritableDatabase("test");
}

// DEMO
import android.content.ContentValues;
import android.content.Context;
import android.util.Log;

import net.sqlcipher.Cursor;
import net.sqlcipher.database.SQLiteDatabase;
import net.sqlcipher.database.SQLiteOpenHelper;

public class DatabaseHelper extends SQLiteOpenHelper {
    private static final String TAG = DatabaseHelper.class.getSimpleName();
    private static final String DB_FILE = "testdb";
    private static final String DB_KEY = "test";

    public static void loadLibs(Context context) {
        SQLiteDatabase.loadLibs(context);
    }

    public static void test(Context context) {
        loadLibs(context);      // 一定要优先调用

        DatabaseHelper helper = new DatabaseHelper(context, DB_FILE, null, 1);
        SQLiteDatabase db = helper.writer();
        helper.insert("赵大", 1);
        helper.insert("李二", 2);
        helper.insert("张三", 3);
        helper.insert("李四", 4);
        helper.insert("王五", 5);
        Cursor cursor = helper.query("赵大");

        if (cursor.getCount() > 0) {
            int nameIndex = cursor.getColumnIndex("name");
            int ageIndex = cursor.getColumnIndex("age");
            while (cursor.moveToNext()) {
                String name = cursor.getString(nameIndex);
                int age = cursor.getInt(ageIndex);
                Log.e(TAG, String.format("name: %s, age: %d", name, age));
            }
        }
    }

    // 带全部参数的构造函数，此构造函数必不可少
    public DatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String sql = "CREATE TABLE test(name VARCHAR(20), age INT)";
        db.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public SQLiteDatabase reader() {
        return this.getReadableDatabase(DB_KEY);
    }

    public SQLiteDatabase writer() {
        return this.getWritableDatabase(DB_KEY);
    }

    public void insert(String name, int age) {
        ContentValues values = new ContentValues();
        values.put("name", name);
        values.put("age", age);
        this.writer().insert("test", null, values);
    }

    public Cursor query(String name) {
        return this.reader().rawQuery("SELECT * FROM test WHERE name=?", new String[]{name});
    }
}