android 中 SQLiteOpenHelper的封装使用详解

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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