android 中 SQLiteOpenHelper的封装使用

在android中常用存储数据的基本就三种，sqlite,SharedPreferences,文件存储，其中针对于对象存储，使用sqlite比较多，因为可以对其进行增删改查。本文主要讲解SQLiteOpenHelper的封装使用，代码引用自https://github.com/iMeiji/Toutiao

具体使用

主要方法包括创建数据库和数据库的升级。
构造函数：包含三个参数，context，name,factory,version
onCreate：主要创建了三张表单
getDatabase：这里其实可以获取两个数据库，分别是getWritableDatabase与getReadableDatabase，这两者的区别不是特别大，都具有对数据库的读写 权限。
getWritableDatabase取得的实例是以读写的方式打开数据库，如果打开的数据库磁盘满了，此时只能读不能写，此时调用了getWritableDatabase的实例，那么将会发生错误（异常）
getReadableDatabase取得的实例是先调用getWritableDatabase以读写的方式打开数据库，如果数据库的磁盘满了，此时返回打开失败，继而用getReadableDatabase的实例以只读的方式去打开数据库
onUpgrade：主要用于数据库的升级，这里面

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final String DB_NAME = "Toutiao";
    private static final int DB_VERSION = 5;
    private static final String CLEAR_TABLE_DATA = "delete from ";
    private static final String DROP_TABLE = "drop table if exists ";
    private static DatabaseHelper instance = null;
    private static SQLiteDatabase db = null;

    private DatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    private static synchronized DatabaseHelper getInstance() {
        if (instance == null) {
            instance = new DatabaseHelper(InitApp.AppContext, DB_NAME, null, DB_VERSION);
        }
        return instance;
    }

    public static synchronized SQLiteDatabase getDatabase() {
        if (db == null) {
            db = getInstance().getWritableDatabase();
        }
        return db;
    }

    public static synchronized void closeDatabase() {
        if (db != null) {
            db.close();
        }
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(NewsChannelTable.CREATE_TABLE);
        db.execSQL(MediaChannelTable.CREATE_TABLE);
        db.execSQL(SearchHistoryTable.CREATE_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        switch (oldVersion) {
            case 1:
                db.execSQL(MediaChannelTable.CREATE_TABLE);
                break;
            case 2:
                db.execSQL(CLEAR_TABLE_DATA + NewsChannelTable.TABLENAME);//删除表中的数据
                break;
            case 3:
                ContentValues values = new ContentValues();
                values.put(NewsChannelTable.ID, "");
                values.put(NewsChannelTable.NAME, "推荐");
                values.put(NewsChannelTable.IS_ENABLE, 0);
                values.put(NewsChannelTable.POSITION, 46);
                db.insert(NewsChannelTable.TABLENAME, null, values);//新建表
                break;
            case 4:
                db.execSQL(SearchHistoryTable.CREATE_TABLE);
                break;
        }
    }
}

表操作的封装

addInitData添加初始化数据
add插入到表中
query查询特定数据

public class NewsChannelDao {

    private SQLiteDatabase db;

    public NewsChannelDao() {
        this.db = DatabaseHelper.getDatabase();
    }

    public void addInitData() {
        String categoryId[] = InitApp.AppContext.getResources().getStringArray(R.array.mobile_news_id);
        String categoryName[] = InitApp.AppContext.getResources().getStringArray(R.array.mobile_news_name);
        for (int i = 0; i < 8; i++) {
            add(categoryId[i], categoryName[i], Constant.NEWS_CHANNEL_ENABLE, i);
        }
        for (int i = 8; i < categoryId.length; i++) {
            add(categoryId[i], categoryName[i], Constant.NEWS_CHANNEL_DISABLE, i);
        }
    }

    public boolean add(String channelId, String channelName, int isEnable, int position) {
        ContentValues values = new ContentValues();
        values.put(NewsChannelTable.ID, channelId);
        values.put(NewsChannelTable.NAME, channelName);
        values.put(NewsChannelTable.IS_ENABLE, isEnable);
        values.put(NewsChannelTable.POSITION, position);
        long result = db.insert(NewsChannelTable.TABLENAME, null, values);
        return result != -1;
    }

    public List<NewsChannelBean> query(int isEnable) {
        Cursor cursor = db.query(NewsChannelTable.TABLENAME, null, NewsChannelTable.IS_ENABLE + "=?",
                new String[]{isEnable + ""}, null, null, null);
        List<NewsChannelBean> list = new ArrayList<>();
        while (cursor.moveToNext()) {
            NewsChannelBean bean = new NewsChannelBean();
            bean.setChannelId(cursor.getString(NewsChannelTable.ID_ID));
            bean.setChannelName(cursor.getString(NewsChannelTable.ID_NAME));
            bean.setIsEnable(cursor.getInt(NewsChannelTable.ID_ISENABLE));
            bean.setPosition(cursor.getInt(NewsChannelTable.ID_POSITION));
            list.add(bean);
        }
        cursor.close();
        return list;
    }

    public List<NewsChannelBean> queryAll() {
        Cursor cursor = db.query(NewsChannelTable.TABLENAME, null, null, null, null, null, null);
        List<NewsChannelBean> list = new ArrayList<>();
        while (cursor.moveToNext()) {
            NewsChannelBean bean = new NewsChannelBean();
            bean.setChannelId(cursor.getString(NewsChannelTable.ID_ID));
            bean.setChannelName(cursor.getString(NewsChannelTable.ID_NAME));
            bean.setIsEnable(cursor.getInt(NewsChannelTable.ID_ISENABLE));
            bean.setPosition(cursor.getInt(NewsChannelTable.ID_POSITION));
            list.add(bean);
        }
        cursor.close();
        return list;
    }

    public void updateAll(List<NewsChannelBean> list) {
    }

    public boolean removeAll() {
        int result = db.delete(NewsChannelTable.TABLENAME, null, null);
        return result != -1;
    }
}

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