我是第一次使用sqlite数据库在Android（Java）中编写应用程序。
两个活动必须保存一些信息，因此我在MySQLiteHelper中都使用它来访问数据库。
我读到here将SQLiteOpenHelper构建为静态数据成员可能是一个很好的做法，所以我这样做了。
静态工厂方法确保任何时候只存在一个DatabaseHelper实例。
我在每个活动中创建一个使用SQLiteOpenHelper方法的getWritableDatabase()，但我不知道在哪里使用close()方法。
我应该在每次修改后或活动结束时使用此方法吗？
谢谢=）
答案 0 :(得分：1)
您需要创建一个类，其中包含所有常用方法，常量，变量等。
然后你必须在这个类中移动“getWritableDatabase（）”并使用。我建议您始终记得关闭db调用。用“close（）”。
但是我在这里使用的实际解决方案如下：
在我的应用程序中，我有不同的数据库适配器，这只是一个例子：
package com.app.android;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DBAdapter {
public static final String KEY_ROWID = "id";
public static final String KEY_NAME = "name";
public static final String KEY_EMAIL = "email";
public static final String TAG = "DBAdapter";
//public static final String DATABASE_NAME = "my_db";
//public static final String DATABASE_TABLE = "contacts";
//public static final int DATABASE_VERSION = 1;
public static final String START_TBL_CREATION = "create table "+Appiah.DATABASE_TABLE+" (_id integer primary key autoincrement, ";
public static final String [] TABLE_COLUMNS_TO_BE_CREATED = new String []{
KEY_NAME+" text not null, ",
KEY_EMAIL+" text not null"
};
public static final String END_TBL_CREATION = ");";
private static final String DATABASE_CREATE = START_TBL_CREATION
+ TABLE_COLUMNS_TO_BE_CREATED[0]
+ TABLE_COLUMNS_TO_BE_CREATED[1]
+ END_TBL_CREATION;
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase db;
public DBAdapter (Context ctx){
this.context = ctx;
DBHelper = new DatabaseHelper(context);//there would be an error initially but just keep going...
}
private static class DatabaseHelper extends SQLiteOpenHelper{//after importing for "SQLiteOpenHelper", Add unimplemented methods
DatabaseHelper(Context context){
super (context, Appiah.DATABASE_NAME, null, Appiah.DATABASE_VERSION);//pls. note : "Appiah" is the class in which all the common methods, variables, etc. are sitting.
}
@Override
public void onCreate(SQLiteDatabase db) {
try{
db.execSQL(DATABASE_CREATE);
}catch(SQLException e){
e.printStackTrace();
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading database from version "+ oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS contacts");
onCreate(db);
}
}
//opens the database
public DBAdapter open() throws SQLiteException{
db = DBHelper.getWritableDatabase();
return this;
}
//closes the database
public void close(){
DBHelper.close();
}
//insert a contact into the database
public long insertContact(String name, String email){
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_NAME, name);
initialValues.put(KEY_EMAIL, email);
return db.insert(Appiah.DATABASE_TABLE, null, initialValues);
}
//deletes a particular contact
public boolean deleteContact(long rowId){
String whereClause = KEY_ROWID + "=" + rowId;
String[] whereArgs = null;
return db.delete(Appiah.DATABASE_TABLE, whereClause, whereArgs) > 0;
}
//retrieves all the contacts
public Cursor getAllContacts(){
String[] columns = new String[]{KEY_ROWID, KEY_NAME, KEY_EMAIL};
String selection = null;
String[] selectionArgs = null;
String groupBy = null;
String having = null;
String orderBy = null;
return db.query(Appiah.DATABASE_TABLE, columns, selection, selectionArgs, groupBy, having, orderBy);
}
//retrieve a particular contact with ID as input
public Cursor getContact_with_ID(long rowId) throws SQLException {
boolean distinct = true;
String table = Appiah.DATABASE_TABLE;
String [] columns = new String []{KEY_ROWID, KEY_NAME, KEY_EMAIL};
String selection = KEY_ROWID + "=" + rowId;
String [] selectionArgs = null;
String groupBy = null;
String having = null;
String orderBy = null;
String limit = null;
Cursor mCursor = db.query(distinct, table, columns, selection, selectionArgs, groupBy, having, orderBy, limit);
if(mCursor != null){
mCursor.moveToFirst();
}
return mCursor;
}
public Cursor getContact_with_nameEntered(String name_str) throws SQLException {
boolean distinct = true;
String table = Appiah.DATABASE_TABLE;
String [] columns = new String []{KEY_ROWID, KEY_NAME, KEY_EMAIL};
String selection = KEY_NAME + "=" + name_str;//check again and do "%" thing to expand scope and increase chances of a name getting found or populated
String [] selectionArgs = null;
String groupBy = null;
String having = null;
String orderBy = null;
String limit = null;
Cursor mCursor = db.query(distinct, table, columns, selection, selectionArgs, groupBy, having, orderBy, limit);
if(mCursor != null){
mCursor.moveToFirst();
}
return mCursor;
}
//update a contact
public boolean updateContact(long rowId, String name, String email){
ContentValues args = new ContentValues();
args.put(KEY_NAME, name);
args.put(KEY_EMAIL, email);
String table = Appiah.DATABASE_TABLE;
ContentValues values = args;
String whereClause = KEY_ROWID + "=" + rowId;
String []whereArgs = null;
return db.update(table, values, whereClause, whereArgs) > 0;
}
/*
TO USE ANY OF THE ABOVE METHODS :
1. type this before in your "onCreate()" : DBAdapter db = new DBAdapter(this);
2. in the special case of getting all contacts to display : do the ff :
db.open();
Cursor c = db.getAllContacts();
if(c.moveToFirst()){
do{
textView.setText("ID : " + c.getString(0) + "\nName : " + c.getString(1) + "\nEmail Address : " + c.getString(2) );
}while(c.moveToNext());//the "while" added ensures that, the looping process occurs
}
db.close();
*/
}
我希望这会有所帮助。它可以变深，但我希望这会有所帮助。一切顺利。