在android中常用存儲數(shù)據(jù)的基本就三種，sqlite,SharedPreferences,文件存儲，其中針對于對象存儲，使用sqlite比較多，因為可以對其進行增刪改查。本文主要講解SQLiteOpenHelper的封裝使用，代碼引用自https://github.com/iMeiji/Toutiao
具體使用
主要方法包括創(chuàng)建數(shù)據(jù)庫和數(shù)據(jù)庫的升級。
構(gòu)造函數(shù)：包含三個參數(shù)，context，name,factory,version
onCreate：主要創(chuàng)建了三張表單
getDatabase：這里其實可以獲取兩個數(shù)據(jù)庫，分別是getWritableDatabase與getReadableDatabase，這兩者的區(qū)別不是特別大，都具有對數(shù)據(jù)庫的讀寫 權(quán)限。
getWritableDatabase取得的實例是以讀寫的方式打開數(shù)據(jù)庫，如果打開的數(shù)據(jù)庫磁盤滿了，此時只能讀不能寫，此時調(diào)用了getWritableDatabase的實例，那么將會發(fā)生錯誤（異常）
getReadableDatabase取得的實例是先調(diào)用getWritableDatabase以讀寫的方式打開數(shù)據(jù)庫，如果數(shù)據(jù)庫的磁盤滿了，此時返回打開失敗，繼而用getReadableDatabase的實例以只讀的方式去打開數(shù)據(jù)庫
onUpgrade：主要用于數(shù)據(jù)庫的升級，這里面
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);//刪除表中的數(shù)據(jù) break; case 3: ContentValues values = new ContentValues(); values.put(NewsChannelTable.ID, ""); values.put(NewsChannelTable.NAME, "推薦"); 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; } }}表操作的封裝
addInitData添加初始化數(shù)據(jù)
add插入到表中
query查詢特定數(shù)據(jù)
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; }}以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持武林網(wǎng)。
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