现在好了完整的代码：
DBOpenHelper：
public class DBOpenHelper extends SQLiteOpenHelper {
private SQLiteDatabase mDatabase;
private static final int DATABASE_VERSION = 1;
private static String DATABASE_NAME = "RTDB";
private static final String DB_TABLE_NAME1 = "playertable";
private static final String DB_TABLE_NAME2 = "itemtable";
private static final String DB_CREATE_TABLE_PT =
"CREATE TABLE IF NOT EXISTS" + DB_TABLE_NAME1 + " ("
+ "ID INT(1) NOT NULL ,"
+ "Name VARCHAR(30) ,"
+ "HP INT(3) ,"
+ "Satisfaction INT(3) ,"
+ "Hygiene INT(1) , "
+ "IsAlive INT(1) "
+ " )"
;
private static final String DB_CREATE_TABLE_IT = "CREATE TABLE IF NOT EXISTS"
+ DB_TABLE_NAME2 + " ("
+ "Money INT(3) ,"
+ "Gas INT(3) ,"
+ "Food INT(3) ,"
+ "Toiletries INT(3) ,"
+ "Spareparts INT(3) ,"
+ "Meds INT(3) ,"
+ "Tents INT(3) ,"
+ "Ration INT(1) ,"
+ "Trabbihp INT(3) ,"
+ "Trabbispeed INT(2) ,"
+ " )"
;
public DBOpenHelper(Context context, String databaseName) {
super(context, databaseName, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
mDatabase = db;
mDatabase = SQLiteDatabase.openOrCreateDatabase(DATABASE_NAME,null);
mDatabase.execSQL(DB_CREATE_TABLE_PT);
mDatabase.execSQL(DB_CREATE_TABLE_IT);
DB.savePlayer(Resource.playerArray);
}
@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
}
}
DB：
public class DB {
static Context context;
private static DBOpenHelper dbHelper = new DBOpenHelper(context, "RTDB");
public static SQLiteDatabase db = dbHelper.getWritableDatabase();
private static ContentValues itemValues = new ContentValues();
private static ContentValues playerValues = new ContentValues();
// Speichern der Spieler in der Datenbank - playerarray muss �bergeben werden
public static void savePlayer(Player player[]){
for(int i = 0; i<3; i++){
playerValues.put("ID", i);
playerValues.put("Name", player[i].getName());
playerValues.put("HP", player[i].getHp());
playerValues.put("Satisfaction", player[i].getsatisfaction());
playerValues.put("Hygiene", player[i].isHygieneInt());
playerValues.put("IsAlive", player[i].isAliveInt());
}
db.insert("playertable", null, playerValues);
}
// Speichern der Items
//TODO Position fehlt noch
public static void saveItems(){
itemValues.put("Money", Resource.money);
itemValues.put("Gas", Resource.gas);
itemValues.put("Food", Resource.food);
itemValues.put("Toiletries", Resource.toiletries);
itemValues.put("Spareparts", Resource.spareparts);
itemValues.put("Meds", Resource.meds);
itemValues.put("Tents", Resource.tents);
itemValues.put("Ration", Resource.ration);
itemValues.put("Trabbihp", Resource.trabbihp);
itemValues.put("Trabbispeed", Resource.trabbispeed);
db.insert("itemtable",null,itemValues);
}
// Hier werden die Items aus der Datenbank abgefragt, der zurueckgelieferte Cursor vie cursorToIntArray() in einen Int Array umgewandelt und dessen Inhalt in die Ressource Klasse geschrieben
public void loadItems(){
Cursor itemCursor = db.query("itemtable", null, null, null, null, null, null);
int[] itemIntArray = cursorToInt(itemCursor, 9);
Resource.money = itemIntArray[0];
Resource.gas = itemIntArray[1];
Resource.food = itemIntArray[2];
Resource.toiletries = itemIntArray[3];
Resource.meds = itemIntArray[4];
Resource.tents = itemIntArray[5];
Resource.ration = itemIntArray[6];
Resource.trabbihp = itemIntArray[7];
Resource.trabbispeed = itemIntArray[8];
}
//Name und Restliche Int-Werte der Playerobjekte werden separat aus der Datenbank geholt und gesetzt
public static void loadPlayer(){
String[] namecolumn = {"Name"};
String[] intcolumn = {"HP, Satisfaction, Hygiene, IsAlive"};
String[] namesToString;
for(int j=0;j<3;j++){
Cursor playerCursorName = db.query("playertable", namecolumn, "ID="+j, null, null, null, null);
namesToString = cursorToString(playerCursorName);
Resource.playerArray[j].setName(namesToString[j]);
}
for(int i=0;i<3;i++){
int[] restToInt;
Cursor playerCursorInt = db.query("playertable", intcolumn, "ID="+i, null, null, null, null);
restToInt = cursorToInt(playerCursorInt,4);
Resource.playerArray[i].setHp(restToInt[i]);
Resource.playerArray[i].setsatisfaction(restToInt[i]);
Resource.playerArray[i].setHygieneInt(restToInt[i]);
Resource.playerArray[i].setAliveInt(restToInt[i]);
}
}
public void dropTables(){
db.execSQL("DROP TABLE 'playertable';");
db.execSQL("DROP TABLE 'itemtable';");
}
private static int[] cursorToInt(Cursor cursor, int n){
int[] results = new int[n];
for(int i=0 ;i<= n-1; i++){
results[i] = cursor.getInt(i);
}
return results;
}
private static String[] cursorToString(Cursor cursor){
String[] results = new String[4];
for(int i=0 ;i<= 3; i++){
results[i] = cursor.getString(i);
}
return results;
}
}
对于新读者：
public static SQLiteDatabase db = dbHelper.getWritableDatabase(); - 语句导致nullpointerexception
DBOpenHelper是一个用于创建数据库的辅助类。它在DB.java中获取实例，我在其中创建了一些操作数据库的方法，如savePlayer等
修改
调试时我发现上面提到的内容 dbHelper对象也指向mContext，mDatabase等 - 正如您可能想象的那样 - null
atm我正试图解决这个问题，但我找不到设置它们的方法
答案 0 :(得分：0)
我认为你没有初始化你的数据库：
private static DBOpenHelper dbHelper = new DBOpenHelper(context);
public static SQLiteDatabase db = dbHelper.getWritableDatabase();
您需要在DBOpenHelper类中有一个构造函数，您可以在其中设置项目的数据库名称。您在DB class中设置数据库，但从不使用它：
private static String filename = "RTDB.sql";
这就是你获得NullPointerException的原因，因为你没有数据库可以获得。
编辑：您可以执行以下操作：
public DBOpenHelper(Context context, String databaseName) {
super(context, databaseName, null, DATABASE_VERSION);
}
以这种方式初始化数据库时，可以设置要使用的数据库的名称。
答案 1 :(得分：0)
static Context context;
private static DBOpenHelper dbHelper = new DBOpenHelper(context, "RTDB.sql");
我想context == null。