应用程序仅在我进入分数窗口时存储数据

Question

我有一个游戏，它在SQLite数据库中存储了它的高分，但它只存储了我在我的应用程序中打开窗口的分数，显示了所述分数，如果我连续玩了2个游戏然后打开高分窗口，它只会显示后来的分数。所以我试着创建一个方法，我可以从主类调用，但我得到空引用错误。以下是我的Highscore课程，可以保存分数。我怎样才能做到这一点，即使没有打开＆＃34;高分＆＃34;也可以保存分数。窗口？

public class highscores extends Activity {
private ListView scorebox1;
private ListView scorebox2;
private ListView scorebox3;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.highscores);
    DBHandler db = new DBHandler(this);
    scorebox1 = (ListView) findViewById(R.id.scorebox1);
    scorebox2 = (ListView) findViewById(R.id.scorebox2);
    scorebox3 = (ListView) findViewById(R.id.scorebox3);



    // Create database helper
    DBHandler mDbHelper = new DBHandler(this);

    // Gets the database in write mode
    SQLiteDatabase db2 = mDbHelper.getWritableDatabase();

    // Create a ContentValues object where column names are the keys,
    // and pet attributes from the editor are the values.
    if(difficutlyFrSQL != ""){
    ContentValues values = new ContentValues();                                 
    values.put(DBHandler.KEY_TIME, difficutlyFrSQL);                            
    values.put(DBHandler.KEY_DIFFICULTY, difficutlyFrSQL2);
    long newRowId = db2.insert(DBHandler.TABLE_DETAIL, null, values);           

    // Show a toast message depending on whether or not the insertion was successful
    if (newRowId == -1) {
        // If the row ID is -1, then there was an error with insertion.
        Toast.makeText(this, "Error with saving test score", Toast.LENGTH_SHORT).show();
    } else {
        // Otherwise, the insertion was successful and we can display a toast with the row ID.
        Toast.makeText(this, "Test score saved with row id: " + newRowId, Toast.LENGTH_SHORT).show();
    }
        difficutlyFrSQL = "";
    }
    Log.d("Reading: ", "Reading all scores..");                                                                         
    ArrayList<String>ar3=new ArrayList<>();                                                                             
    ar3=db.getAllScores(3);
    Collections.sort(ar3);
    Collections.reverse(ar3);
    ArrayAdapter<String>ap3=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,ar3);
        scorebox1.setAdapter(ap3);
    ArrayList<String>ar2=new ArrayList<>();
    ar2=db.getAllScores(2);
    Collections.sort(ar2);
    Collections.reverse(ar2);
    ArrayAdapter<String>ap2=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,ar2);
    scorebox2.setAdapter(ap2);
    ArrayList<String>ar1=new ArrayList<>();
    ar1=db.getAllScores(1);
    Collections.sort(ar1);
    Collections.reverse(ar1);
    ArrayAdapter<String>ap1=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,ar1);
    scorebox3.setAdapter(ap1);
}
}