什么是现有 SQLite 数据库的完整 Android 数据库助手类？
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What is a Full Android Database Helper class for an existing SQLite database?
提问by Biff MaGriff
I'm trying to deploy an application with an existing SQLite database.
我正在尝试使用现有的 SQLite 数据库部署应用程序。
I've read through and attempted to implement several samples online however I've found that they are always missing some code and either do not compile or work as advertised.
我已经通读并尝试在线实现几个示例，但是我发现它们总是缺少一些代码，并且要么不能编译，要么不能像宣传的那样工作。
Does anyone have a Full Android Database Helper class for deploying an existing SQLite database on Android?
有没有人有一个完整的 Android 数据库助手类来在 Android 上部署现有的 SQLite 数据库？
回答by Biff MaGriff
This is what I came up with, hope it helps others that were having troubles.
这就是我想出来的，希望它可以帮助其他遇到麻烦的人。
package com.MyPackage;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.UUID;
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 AnyDBAdapter {
private static final String TAG = "AnyDBAdapter";
private DatabaseHelper mDbHelper;
private static SQLiteDatabase mDb;
//make sure this matches the
//package com.MyPackage;
//at the top of this file
private static String DB_PATH = "/data/data/com.MyPackage/databases/";
//make sure this matches your database name in your assets folder
// my database file does not have an extension on it
// if yours does
// add the extention
private static final String DATABASE_NAME = "data";
//Im using an sqlite3 database, I have no clue if this makes a difference or not
private static final int DATABASE_VERSION = 3;
private final Context adapterContext;
public AnyDBAdapter(Context context) {
this.adapterContext = context;
}
public AnyDBAdapter open() throws SQLException {
mDbHelper = new DatabaseHelper(adapterContext);
try {
mDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
mDbHelper.openDataBase();
} catch (SQLException sqle) {
throw sqle;
}
return this;
}
//Usage from outside
// AnyDBAdapter dba = new AnyDBAdapter(contextObject); //in my case contextObject is a Map
// dba.open();
// Cursor c = dba.ExampleSelect("Rawr!");
// contextObject.startManagingCursor(c);
// String s1 = "", s2 = "";
// if(c.moveToFirst())
// do {
// s1 = c.getString(0);
// s2 = c.getString(1);
// } while (c.moveToNext());
// dba.close();
public Cursor ExampleSelect(string myVariable)
{
String query = "SELECT locale, ? FROM android_metadata";
return mDb.rawQuery(query, new String[]{myVariable});
}
//Usage
// AnyDBAdatper dba = new AnyDBAdapter(contextObjecT);
// dba.open();
// dba.ExampleCommand("en-CA", "en-GB");
// dba.close();
public void ExampleCommand(String myVariable1, String myVariable2)
{
String command = "INSERT INTO android_metadata (locale) SELECT ? UNION ALL SELECT ?";
mDb.execSQL(command, new String[]{ myVariable1, myVariable2});
}
public void close() {
mDbHelper.close();
}
private static class DatabaseHelper extends SQLiteOpenHelper {
Context helperContext;
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
helperContext = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading database!!!!!");
//db.execSQL("");
onCreate(db);
}
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
} else {
//make sure your database has this table already created in it
//this does not actually work here
/*
* db.execSQL("CREATE TABLE IF NOT EXISTS \"android_metadata\" (\"locale\" TEXT DEFAULT 'en_US')"
* );
* db.execSQL("INSERT INTO \"android_metadata\" VALUES ('en_US')"
* );
*/
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
public SQLiteDatabase getDatabase() {
String myPath = DB_PATH + DATABASE_NAME;
return SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
}
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DATABASE_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null ? true : false;
}
private void copyDataBase() throws IOException {
// Open your local db as the input stream
InputStream myInput = helperContext.getAssets().open(DATABASE_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DATABASE_NAME;
// Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
// transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
// Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException {
// Open the database
String myPath = DB_PATH + DATABASE_NAME;
mDb = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
}
@Override
public synchronized void close() {
if (mDb != null)
mDb.close();
super.close();
}
}
}
回答by plugmind
DatabaseHelper dbHelper = new DatabaseHelper(getApplicationContext());
Make sure you create DatabaseHelper object once during application lifetime and reuse it.
确保在应用程序生命周期内创建一次 DatabaseHelper 对象并重用它。
For reading data:
读取数据：
SQLiteDatabase db = dbHelper.getReadableDatabase();
For reading/modification data:
读取/修改数据：
SQLiteDatabase db = dbHelper.getWritableDatabase();
next use insert(), query(), update(), delete()methods of SQLiteDatabase object:
接下来使用SQLiteDatabase 对象的insert(), query(), update(),delete()方法：
http://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html
http://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html
You also should not create the database by directly accesssing the sqlite file what you do in createNewDatabase method. Use execSQL() method of SQLiteDatabase object in your onCreate(...) method. Execute your CREATE TABLE queries there.
您也不应该像在 createNewDatabase 方法中那样直接访问 sqlite 文件来创建数据库。在 onCreate(...) 方法中使用 SQLiteDatabase 对象的 execSQL() 方法。在那里执行您的 CREATE TABLE 查询。
