从 AsyncTask 类的 onPostExecute 方法返回值 [英] Return value from AsyncTask class onPostExecute method

问题描述

好的，现在我有 Class A 包含一些微调器，这些值将由 Class B 填充，扩展 AsnycTask 抓取微调器来自 Web 服务的值.在 B 类中，我设法检索值，显示在 Toast 中.现在的问题是如何将这些微调器值传递回 A 类?

Ok so now I have Class A that contains some spinners that values will be populated by Class B that extends AsnycTask which grabs the spinner values from a web service. In class B i manage to retrieve the values, showing in a Toast. The problem now is how do I pass those spinner values back to Class A?

我试过了

AsyncTask 中的 OnPostExcecute 方法可以返回值吗?

通过将 Class A 传递给 Class B 并将值存储在 Class A 的公共变量中，如下所示

by passing Class A to Class B and store the value in a public variable of Class A like below

@Override
protected void onPostExecute(String result)
{
  classA.classAvariable = result;
}

然而，每当我尝试读取 classAvariable 时，我总是得到一个 NullPointer Exception.似乎变量从未分配过结果.出于可读性目的，我需要将 Class B 分开，而不是用作内联类.

However whenever I try to read the classAvariable i always get a NullPointer Exception. Seems like the variable was never assigned with the result. For readability purpose I needed to seperate Class B instead of using as an inline class.

我的 Java 程序员同胞有什么想法吗?

Any ideas my fellow Java programmers?

推荐答案

我猜您是在尝试在设置 A 类变量之前读取它..尝试使用回调来做到这一点..在回调函数中传递值并刷新您的微调器..

I guess you are trying to read class A variable before it is being set.. Try to do it using callbacks..in the callback function pass the values and refresh your spinners..

您可以创建interface，将其传递给AsyncTask(在构造函数中)，然后在onPostExecute

You can create interface, pass it to AsyncTask (in constructor), and then call method in onPostExecute

例如:

您的界面:

public interface OnTaskCompleted{
    void onTaskCompleted(values);
}

您的活动:

public YourActivity implements OnTaskCompleted{
    //your Activity
    YourTask  task = new YourTask(this); // here is the initalization code for your asyncTask
}

还有你的 AsyncTask:

And your AsyncTask:

public YourTask extends AsyncTask<Object,Object,Object>{ //change Object to required type
    private OnTaskCompleted listener;

    public YourTask(OnTaskCompleted listener){
        this.listener=listener;
    }

    //required methods

    protected void onPostExecute(Object o){
        //your stuff
        listener.onTaskCompleted(values);
    }
}

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