我有两门课。我的主活动和一个扩展AsyncTask,现在在我的主活动中,我需要从AsyncTask中的OnPostExecute()获得结果。如何将结果传递给我的主活动?

下面是示例代码。

我的主要活动。

public class MainActivity extends Activity{

    AasyncTask asyncTask = new AasyncTask();

    @Override
    public void onCreate(Bundle aBundle) {
        super.onCreate(aBundle);            

        //Calling the AsyncTask class to start to execute.  
        asyncTask.execute(a.targetServer); 

        //Creating a TextView.
        TextView displayUI = asyncTask.dataDisplay;
        displayUI = new TextView(this);
        this.setContentView(tTextView); 
    }

}

这是AsyncTask类

public class AasyncTask extends AsyncTask<String, Void, String> {

TextView dataDisplay; //store the data  
String soapAction = "http://sample.com"; //SOAPAction header line. 
String targetServer = "https://sampletargeturl.com"; //Target Server.

//SOAP Request.
String soapRequest = "<sample XML request>";    



@Override
protected String doInBackground(String... string) {

String responseStorage = null; //storage of the response

try {


    //Uses URL and HttpURLConnection for server connection. 
    URL targetURL = new URL(targetServer);
    HttpURLConnection httpCon = (HttpURLConnection) targetURL.openConnection();
    httpCon.setDoOutput(true);
    httpCon.setDoInput(true);
    httpCon.setUseCaches(false); 
    httpCon.setChunkedStreamingMode(0);

    //properties of SOAPAction header
    httpCon.addRequestProperty("SOAPAction", soapAction);
    httpCon.addRequestProperty("Content-Type", "text/xml; charset=utf-8"); 
    httpCon.addRequestProperty("Content-Length", "" + soapRequest.length());
    httpCon.setRequestMethod(HttpPost.METHOD_NAME);


    //sending request to the server.
    OutputStream outputStream = httpCon.getOutputStream(); 
    Writer writer = new OutputStreamWriter(outputStream);
    writer.write(soapRequest);
    writer.flush();
    writer.close();


    //getting the response from the server
    InputStream inputStream = httpCon.getInputStream(); 
    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
    ByteArrayBuffer byteArrayBuffer = new ByteArrayBuffer(50);

    int intResponse = httpCon.getResponseCode();

    while ((intResponse = bufferedReader.read()) != -1) {
        byteArrayBuffer.append(intResponse);
    }

    responseStorage = new String(byteArrayBuffer.toByteArray()); 

    } catch (Exception aException) {
    responseStorage = aException.getMessage(); 
    }
    return responseStorage;
}

protected void onPostExecute(String result) {

    aTextView.setText(result);

}       

}   

当前回答

你可以调用AsyncTask的get()方法(或者重载的get(long, TimeUnit))。此方法将阻塞,直到AsyncTask完成它的工作,此时它将返回Result。

在创建/启动异步任务和调用get方法之间做其他工作是明智的,否则你不能非常有效地利用异步任务。

其他回答

希望你已经读过了,如果没有,请阅读。

https://developer.android.com/reference/android/os/AsyncTask

根据结果数据的性质,您应该选择您能想到的最佳选项。

使用接口是一个很好的选择

其他的选择是…

If the AsyncTask class is defined inside the very class you want to use the result in.Use a static global variable or get() , use it from outer class (volatile variable if necessary). but should be aware of the AsyncTask progress or should at least make sure that it have finished the task and result is available through global variable / get() method. you may use polling, onProgressUpdate(Progress...), synchronization or interfaces (Which ever suits best for you) If the Result is compatible to be a sharedPreference entry or it is okay to be saved as a file in the memory you could save it even from the background task itself and could use the onPostExecute() method to get notified when the result is available in the memory. If the string is small enough, and is to be used with start of an activity. it is possible to use intents (putExtra()) within onPostExecute() , but remember that static contexts aren't that safe to deal with. If possible, you can call a static method from the onPostExecute() method, with the result being your parameter

你可以调用AsyncTask的get()方法(或者重载的get(long, TimeUnit))。此方法将阻塞,直到AsyncTask完成它的工作,此时它将返回Result。

在创建/启动异步任务和调用get方法之间做其他工作是明智的,否则你不能非常有效地利用异步任务。

为什么人们把事情搞得这么难。

这应该足够了。

不要在异步任务上实现onPostExecute,而是在Activity上实现它:

public class MainActivity extends Activity 
{

@Override
public void onCreate(Bundle savedInstanceState) {

    //execute the async task 
    MyAsyncTask task = new MyAsyncTask(){
            protected void onPostExecute(String result) {
                //Do your thing
            }       

    }

    task.execute("Param");

}


}

您需要使用“协议”将数据委托或提供给AsynTask。

委托和数据源

委托是一个对象,当另一个对象在程序中遇到事件时,它代表另一个对象或与另一个对象协调行动。(苹果定义)

协议是定义一些方法来委托一些行为的接口。

这是一个完整的例子!!

您可以编写自己的侦听器。它和HelmiB的答案一样,但看起来更自然:

创建监听器接口:

public interface myAsyncTaskCompletedListener {
    void onMyAsynTaskCompleted(int responseCode, String result);
}

然后写你的异步任务:

public class myAsyncTask extends AsyncTask<String, Void, String> {

    private myAsyncTaskCompletedListener listener;
    private int responseCode = 0;

    public myAsyncTask() {
    }

    public myAsyncTask(myAsyncTaskCompletedListener listener, int responseCode) {
        this.listener = listener;
        this.responseCode = responseCode;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }


    @Override
    protected String doInBackground(String... params) {
        String result;
        String param = (params.length == 0) ? null : params[0];
        if (param != null) {
            // Do some background jobs, like httprequest...
            return result;
        }
        return null;
    }

    @Override
    protected void onPostExecute(String finalResult) {
        super.onPostExecute(finalResult);
        if (!isCancelled()) {
            if (listener != null) {
                listener.onMyAsynTaskCompleted(responseCode, finalResult);
            }
        }
    }
}

最后在activity中实现监听器:

public class MainActivity extends AppCompatActivity implements myAsyncTaskCompletedListener {

    @Override
    public void onMyAsynTaskCompleted(int responseCode, String result) {

        switch (responseCode) {
            case TASK_CODE_ONE: 
                // Do something for CODE_ONE
                break;
            case TASK_CODE_TWO:
                // Do something for CODE_TWO
                break;
            default: 
                // Show some error code
        }        
    }

这是你如何调用asyncTask:

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // Some other codes...
        new myAsyncTask(this,TASK_CODE_ONE).execute("Data for background job");
        // And some another codes...
}