There are basically three types of data storage commonly used in Android: sqlite, SharedPreferences, file storage. Among them, SQLite is used more for object storage, because it can be added, deleted, modified and checked. This article mainly explains the encapsulation and use of SQLiteOpenHelper, and the code is referenced from/iMeiji/Toutiao
Specific use
The main methods include creating databases and upgrades to the database.
Constructor: contains three parameters, context, name, factory, version
onCreate: mainly creates three forms
getDatabase: Here you can actually get two databases, namely getWritableDatabase and getReadableDatabase. The difference between these two is not particularly big, and both have read and write permissions to the database.
The instance obtained by getWritableDatabase opens the database in a read-write manner. If the opened database disk is full, it can only read but not write at this time. When the instance of getWritableDatabase is called, an error (exception) will occur (exception)
The instance obtained by getReadableDatabase is to call getWritableDatabase to open the database in a read-write manner. If the database disk is full, the return opening failure is now possible. Then use the getReadableDatabase instance to open the database in a read-only manner.
onUpgrade: mainly used for database upgrade, here
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, factory, int version) {
super(context, name, factory, version);
}
private static synchronized DatabaseHelper getInstance() {
if (instance == null) {
instance = new DatabaseHelper(, 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) {
();
}
}
@Override
public void onCreate(SQLiteDatabase db) {
(NewsChannelTable.CREATE_TABLE);
(MediaChannelTable.CREATE_TABLE);
(SearchHistoryTable.CREATE_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
switch (oldVersion) {
case 1:
(MediaChannelTable.CREATE_TABLE);
break;
case 2:
(CLEAR_TABLE_DATA + );//Delete the data in the table break;
case 3:
ContentValues values = new ContentValues();
(, "");
(, "recommend");
(NewsChannelTable.IS_ENABLE, 0);
(, 46);
(, null, values);// Create a new table break;
case 4:
(SearchHistoryTable.CREATE_TABLE);
break;
}
}
}
Encapsulation of table operations
addInitData adds initialization data
add insert into table
query specific data
public class NewsChannelDao {
private SQLiteDatabase db;
public NewsChannelDao() {
= ();
}
public void addInitData() {
String categoryId[] = ().getStringArray(.mobile_news_id);
String categoryName[] = ().getStringArray(.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 < ; 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();
(, channelId);
(, channelName);
(NewsChannelTable.IS_ENABLE, isEnable);
(, position);
long result = (, null, values);
return result != -1;
}
public List<NewsChannelBean> query(int isEnable) {
Cursor cursor = (, null, NewsChannelTable.IS_ENABLE + "=?",
new String[]{isEnable + ""}, null, null, null);
List<NewsChannelBean> list = new ArrayList<>();
while (()) {
NewsChannelBean bean = new NewsChannelBean();
((NewsChannelTable.ID_ID));
((NewsChannelTable.ID_NAME));
((NewsChannelTable.ID_ISENABLE));
((NewsChannelTable.ID_POSITION));
(bean);
}
();
return list;
}
public List<NewsChannelBean> queryAll() {
Cursor cursor = (, null, null, null, null, null, null);
List<NewsChannelBean> list = new ArrayList<>();
while (()) {
NewsChannelBean bean = new NewsChannelBean();
((NewsChannelTable.ID_ID));
((NewsChannelTable.ID_NAME));
((NewsChannelTable.ID_ISENABLE));
((NewsChannelTable.ID_POSITION));
(bean);
}
();
return list;
}
public void updateAll(List<NewsChannelBean> list) {
}
public boolean removeAll() {
int result = (, null, null);
return result != -1;
}
}
The above is all the content of this article. I hope it will be helpful to everyone's study and I hope everyone will support me more.