java如何从回调接口获取对象值？

Question

第一个问题，我从java编程开始

我有一个AssyncTask方法，它使用一个接口在完成后从OnPostExecute调用用户信息。这一切都很好，但是一旦我收到关于我的主要活动的数据，我就无法提取用户的done方法

我张贴代码以便更好地理解

 new FetchUserDataAsyncTask(user, new GetUserCallBack() {

                @Override
                public void done(User returnedUser) {

                    String usernameRet = returnedUser.username;
                    String passwordRet = returnedUser.password;
                }

            });

以及界面：

public interface GetUserCallBack {

    public abstract void done(User returnedUser);
}

AsynkTask：

public class FetchUserDataAsyncTask extends AsyncTask<Void, Void, User> {

    RequestHandler rh = new RequestHandler();
    User user;
    User ret_user;
    GetUserCallBack usercallback;


    public FetchUserDataAsyncTask(User user, GetUserCallBack usercallback){
        this.user  = user;
        this.usercallback = usercallback;

    }


    @Override
    protected User doInBackground(Void... params) {
        try {
            HashMap<String, String> dataToSend = new HashMap<>();
            dataToSend.put("username", user.username);
            dataToSend.put("password", user.password);
            ret_user = rh.sendGetRequest("www.fjrmy.php", dataToSend);
            return null;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return ret_user;
    }

    @Override
    protected void onPostExecute(User returnedUser) {
        super.onPostExecute(ret_user);
        usercallback.done(returnedUser);
    }


}

我只想“提取”usernameRet和passwordRet来处理它们。可能吗

非常感谢你

Answer 1

您的AsnycTask始终返回null。 删除此行：

 return null;

还不需要在AsyncTask中保留返回值。这应该起作用：

public class FetchUserDataAsyncTask extends AsyncTask<Void, Void, User> {

    RequestHandler rh = new RequestHandler();
    User user;
    GetUserCallBack usercallback;


    public FetchUserDataAsyncTask(User user, GetUserCallBack usercallback){
        this.user = user;
        this.usercallback = usercallback;

    }


    @Override
    protected User doInBackground(Void... params) {
        try {
            HashMap<String, String> dataToSend = new HashMap<>();
            dataToSend.put("username", user.username);
            dataToSend.put("password", user.password);
            return rh.sendGetRequest("www.fjrmy.php", dataToSend);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(User returnedUser) {
        super.onPostExecute(returnedUser);
        usercallback.done(returnedUser);
    }


}

Answer 2

在AsyncTask中，在try块中返回null。如果rh.sendGetRequest方法成功，则将其更改为return ret_user;

在示例代码中，您似乎也没有在AsyncTask上调用execute

final User user = new User(); < - declare a field or outer variable

FetchUserDataAsyncTask task = new FetchUserDataAsyncTask(user, new GetUserCallBack() {
      @Override
      public void done(User retUser) {
          user.username = retUser.username; // < - set variables
          user.password = retUser.password; // < -
      }
});
task.execute(); // <  - missing this