我是Libgdx的新手,正在尝试在我的游戏中使用数据库,并遇到了麻烦。
我搜索了一下,想找一个使用Libgdx使SQLite在Android和桌面应用程序中工作的教程,但没有找到一个易于理解的。
上次我在Android中使用数据库时,我创建了一个继承自SQLiteOpenHelper
的类。
是否有一种简单的方法来使用Libgdx实现相同的功能?或者至少,有人可以指导我一步一步的教程或类似的东西吗?
编辑
我忘了说我正在寻找一些能让我像SQLiteOpenHelper
一样管理版本的内容。换句话说,当我更改代码中的数据库版本时,我希望在apk安装时在Android上重新创建我的数据库。
解决方案
根据@42n4
的回答,我成功地使用SQLiteOpenHelper
在Android应用程序和JDBC
上连接到SQLite数据库。
首先,我为桌面应用程序和Android应用程序创建了一个“通用类”:
//General class that needs to be implemented on Android and Desktop Applications
public abstract class DataBase {
protected static String database_name="recycling_separation";
protected static DataBase instance = null;
protected static int version=1;
//Runs a sql query like "create".
public abstract void execute(String sql);
//Identical to execute but returns the number of rows affected (useful for updates)
public abstract int executeUpdate(String sql);
//Runs a query and returns an Object with all the results of the query. [Result Interface is defined below]
public abstract Result query(String sql);
public void onCreate(){
//Example of Highscore table code (You should change this for your own DB code creation)
execute("CREATE TABLE 'highscores' ('_id' INTEGER PRIMARY KEY NOT NULL , 'name' VARCHAR NOT NULL , 'score' INTEGER NOT NULL );");
execute("INSERT INTO 'highscores'(name,score) values ('Cris',1234)");
//Example of query to get DB data of Highscore table
Result q=query("SELECT * FROM 'highscores'");
if (!q.isEmpty()){
q.moveToNext();
System.out.println("Highscore of "+q.getString(q.getColumnIndex("name"))+": "+q.getString(q.getColumnIndex("score")));
}
}
public void onUpgrade(){
//Example code (You should change this for your own DB code)
execute("DROP TABLE IF EXISTS 'highscores';");
onCreate();
System.out.println("DB Upgrade maded because I changed DataBase.version on code");
}
//Interface to be implemented on both Android and Desktop Applications
public interface Result{
public boolean isEmpty();
public boolean moveToNext();
public int getColumnIndex(String name);
public float getFloat(int columnIndex);
[...]
}
}
接着,我为桌面应用程序创建了一个DatabaseDesktop
类:
public class DatabaseDesktop extends DataBase{
protected Connection db_connection;
protected Statement stmt;
protected boolean nodatabase=false;
public DatabaseDesktop() {
loadDatabase();
if (isNewDatabase()){
onCreate();
upgradeVersion();
} else if (isVersionDifferent()){
onUpgrade();
upgradeVersion();
}
}
public void execute(String sql){
try {
stmt.execute(sql);
} catch (SQLException e) {
e.printStackTrace();
}
}
public int executeUpdate(String sql){
try {
return stmt.executeUpdate(sql);
} catch (SQLException e) {
e.printStackTrace();
}
return 0;
}
public Result query(String sql) {
try {
return new ResultDesktop(stmt.executeQuery(sql));
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
private void loadDatabase(){
File file = new File (database_name+".db");
if(!file.exists())
nodatabase=true;
try {
Class.forName("org.sqlite.JDBC");
db_connection = DriverManager.getConnection("jdbc:sqlite:"+database_name+".db");
stmt = db_connection.createStatement();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
}
private void upgradeVersion() {
execute("PRAGMA user_version="+version);
}
private boolean isNewDatabase() {
return nodatabase;
}
private boolean isVersionDifferent(){
Result q=query("PRAGMA user_version");
if (!q.isEmpty())
return (q.getInt(1)!=version);
else
return true;
}
public class ResultDesktop implements Result{
ResultSet res;
boolean called_is_empty=false;
public ResultDesktop(ResultSet res) {
this.res = res;
}
public boolean isEmpty() {
try {
if (res.getRow()==0){
called_is_empty=true;
return !res.next();
}
return res.getRow()==0;
} catch (SQLException e) {
e.printStackTrace();
}
return false;
}
public boolean moveToNext() {
try {
if (called_is_empty){
called_is_empty=false;
return true;
} else
return res.next();
} catch (SQLException e) {
e.printStackTrace();
}
return false;
}
public int getColumnIndex(String name) {
try {
return res.findColumn(name);
} catch (SQLException e) {
e.printStackTrace();
}
return 0;
}
public float getFloat(int columnIndex) {
try {
return res.getFloat(columnIndex);
} catch (SQLException e) {
e.printStackTrace();
}
return 0;
}
[...]
}
}
为 Android 应用程序设计的 DatabaseAndroid
数据库。
public class DatabaseAndroid extends DataBase{
protected SQLiteOpenHelper db_connection;
protected SQLiteDatabase stmt;
public DatabaseAndroid(Context context) {
db_connection = new AndroidDB(context, database_name, null, version);
stmt=db_connection.getWritableDatabase();
}
public void execute(String sql){
stmt.execSQL(sql);
}
public int executeUpdate(String sql){
stmt.execSQL(sql);
SQLiteStatement tmp = stmt.compileStatement("SELECT CHANGES()");
return (int) tmp.simpleQueryForLong();
}
public Result query(String sql) {
ResultAndroid result=new ResultAndroid(stmt.rawQuery(sql,null));
return result;
}
class AndroidDB extends SQLiteOpenHelper {
public AndroidDB(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
}
public void onCreate(SQLiteDatabase db) {
stmt=db;
DatabaseAndroid.this.onCreate();
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
stmt=db;
DatabaseAndroid.this.onUpgrade();
}
}
public class ResultAndroid implements Result{
Cursor cursor;
public ResultAndroid(Cursor cursor) {
this.cursor=cursor;
}
public boolean isEmpty() {
return cursor.getCount()==0;
}
public int getColumnIndex(String name) {
return cursor.getColumnIndex(name);
}
public String[] getColumnNames() {
return cursor.getColumnNames();
}
public float getFloat(int columnIndex) {
return cursor.getFloat(columnIndex);
}
[...]
}
}
最后,我更改了安卓和桌面应用程序的主要类:
public class Main extends AndroidApplication {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
initialize(new MyGame(new DatabaseAndroid(this.getBaseContext())), false);
}
}
public class Main {
public static void main(String[] args) {
new LwjglApplication(new MyGame(new DatabaseDesktop()), "Example", MyGame.SCREEN_WIDTH, MyGame.SCREEN_HEIGHT,false);
}
}
请注意:我使用
PRAGMA user_version
像 SQLiteOpenHelper
中发生的版本管理一样。这样,当我需要升级它时,我只需更改 DataBase
类的版本。我没有放置我在
Result
上制作的所有方法,但是我放置了我认为更重要的方法。
StatusData
的类,是吗?在Android中,我可以像以前一样使用SQLiteOpenHelper
。那么,在桌面应用程序中怎么办呢?例如,当StatusData
的数据库版本发生变化时,我如何让桌面应用程序重新创建DB? - Cristiano SantosSQLiteOpenHelper
,在桌面上使用JDBC
做同样的事情,它们都是在名为StatusData
或类似的类中创建的。对吗? - Cristiano Santos