减少数据库问题

Question

我目前的代码存在问题。我在android工作。这是我的学校实验室之一，但我不知道为什么它不起作用。它与我在上一个实验室中创建的聊天窗口的数据库有关。我想将所有聊天内容存储到数据库中。我一直很难在编程中使用数据库。我发布了下面的两个课程。如果有人能提供帮助，我们将非常感激。

public class ChatWindow extends Activity {

Button send;
ListView chat;
EditText message;
ArrayList<String> list;
String addText;
ChatAdapter messageAdapter;
public static final String ACTIVITY_NAME = "ChatWindow";
String returnedMessage;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_chat_window);
    send = (Button) findViewById(R.id.send_button);
    chat = (ListView) findViewById(listView);
    message = (EditText) findViewById(R.id.message_text);
    list = new ArrayList<>();
    messageAdapter = new ChatAdapter( this );
    chat.setAdapter(messageAdapter);
    ChatDatabaseHelper chatDH = new ChatDatabaseHelper(ChatWindow.this.getApplicationContext());
    final SQLiteDatabase myDatabase = chatDH.getWritableDatabase();



    Cursor cursor = myDatabase.query(false, MY_TABLE, columns, null, null, null, null, null, null);

    int numOfResults = cursor.getCount();
    int numOfColumns = cursor.getColumnCount();
    int getMessageIndex = cursor.getColumnIndex(KEY_MESSAGE);
    int array[] = new int[] {R.id.message_text};
    SimpleCursorAdapter adptr = new SimpleCursorAdapter(this, R.layout.activity_chat_window, cursor, new String[] {KEY_ID, KEY_MESSAGE}, array, 0 );



    chat.setAdapter(adptr);

    for(int i = 0; i < numOfResults; i++){
        returnedMessage = cursor.getString(getMessageIndex);
        cursor.moveToNext();
    }

    cursor.moveToFirst();

    while(!cursor.isAfterLast()){
        returnedMessage = cursor.getString(getMessageIndex);
        cursor.moveToNext();
    }


    cursor.close();


    send.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            addText = message.getText().toString();
            list.add(addText);
            messageAdapter.notifyDataSetChanged();
            message.setText("");
            ContentValues newValue = new ContentValues();
            newValue.put(KEY_MESSAGE, addText);
            myDatabase.insert(MY_TABLE, "", newValue);


        }
    });
}


private class ChatAdapter extends ArrayAdapter<String> {

    public ChatAdapter(Context ctx) {
        super(ctx, 0);
    }

    public int getCount(){
        return list.size();
    }

    public String getItem(int position){
        return list.get(position);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent){
        LayoutInflater inflater = ChatWindow.this.getLayoutInflater();

        View result;

        if(position%2 == 0)
            result = inflater.inflate(R.layout.chat_row_incoming, null);
        else
            result = inflater.inflate(R.layout.chat_row_outgoing, null);

        TextView message = (TextView)result.findViewById(R.id.message_text);
        message.setText(   getItem(position)  );
        return result;


    }

}
}

public class ChatDatabaseHelper extends SQLiteOpenHelper {


private static final String DATABASE_NAME = "Messages.db";
private static final int VERSION_NUM = 1;
public static final String KEY_ID = "ID";
public static final String KEY_MESSAGE = "Message";
public static final String MY_TABLE = "MyTable";
public static final String [] columns = new String[] {KEY_ID, KEY_MESSAGE};

public ChatDatabaseHelper(Context ctx) {
    super(ctx, DATABASE_NAME, null, VERSION_NUM);
}


public void onCreate(SQLiteDatabase db) {
    String CREAT_TABLE = "CREATE TABLE " + MY_TABLE + "("
            + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
            + KEY_MESSAGE + " TEXT " + ");";
    db.execSQL(CREAT_TABLE);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + MY_TABLE);
    onCreate(db);
}







}