如何将OnPostExecute（）的结果获取到主activity，因为AsyncTask是一个单独的类？

Question

我有两个类。我的主要activity和扩展AsyncTask的一个，现在在我的主要activity中，我需要从AsyncTask中的OnPostExecute()获得结果。我怎样才能通过或得到结果到我的主要activity？

下面是示例代码。

我的主要activity。

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);

}       

}   

Answer 1

有几种选择：

>

在activity类中嵌套AsyncTask类。假设您不在多个活动中使用相同的任务，这是最简单的方法。您的所有代码保持不变，只需将现有的任务类移动为activity类中的嵌套类。

public class MyActivity extends Activity {
    // existing Activity code
    ...

    private class MyAsyncTask extends AsyncTask<String, Void, String> {
        // existing AsyncTask code
        ...
    }
}

为您的AsyncTask创建一个自定义构造函数，它引用您的activity。您可以使用类似new MyAsyncTask(this).execute(param1,param2)的内容实例化任务。

public class MyAsyncTask extends AsyncTask<String, Void, String> {
    private Activity activity;

    public MyAsyncTask(Activity activity) {
        this.activity = activity;
    }

    // existing AsyncTask code
    ...
}

Answer 2

容易：

>

创建接口类，其中字符串输出是可选的，也可以是任何要返回的变量。

public interface AsyncResponse {
    void processFinish(String output);
}

转到AsyncTask类，并将interfaceAsyncResponse声明为字段：

public class MyAsyncTask extends AsyncTask<Void, Void, String> {
  public AsyncResponse delegate = null;

    @Override
    protected void onPostExecute(String result) {
      delegate.processFinish(result);
    }
 }

在您的主要activity中，您需要实现接口异步响应。

public class MainActivity implements AsyncResponse{
  MyAsyncTask asyncTask =new MyAsyncTask();

  @Override
  public void onCreate(Bundle savedInstanceState) {

     //this to set delegate/listener back to this class
     asyncTask.delegate = this;

     //execute the async task 
     asyncTask.execute();
  }

  //this override the implemented method from asyncTask
  @Override
  void processFinish(String output){
     //Here you will receive the result fired from async class 
     //of onPostExecute(result) method.
   }
 }

更新

我不知道你们很多人都这么喜欢这个。下面是使用接口的简单而方便的方法。

仍然使用相同的接口。另外，您可以将其组合到AsyncTask类中。

在AsyncTask类中：

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

  // you may separate this or combined to caller class.
  public interface AsyncResponse {
        void processFinish(String output);
  }

  public AsyncResponse delegate = null;

    public MyAsyncTask(AsyncResponse delegate){
        this.delegate = delegate;
    }

    @Override
    protected void onPostExecute(String result) {
      delegate.processFinish(result);
    }
}

在activity类中执行此操作

public class MainActivity extends Activity {

   MyAsyncTask asyncTask = new MyAsyncTask(new AsyncResponse(){

     @Override
     void processFinish(String output){
     //Here you will receive the result fired from async class 
     //of onPostExecute(result) method.
     }
  }).execute();

 }

或者，在activity上重新实现接口

public class MainActivity extends Activity 
    implements AsyncResponse{

    @Override
    public void onCreate(Bundle savedInstanceState) {

        //execute the async task 
        new MyAsyncTask(this).execute();
    }

    //this override the implemented method from AsyncResponse
    @Override
    void processFinish(String output){
        //Here you will receive the result fired from async class 
        //of onPostExecute(result) method.
    }
}

正如您在上面看到的两个解决方案，第一个和第三个，它需要创建方法processFinish，另一个，方法在caller参数内部。第三种更整洁，因为没有嵌套的匿名类。希望这有帮助

提示：将字符串输出、字符串响应和字符串结果更改为不同的匹配类型，以获得不同的对象。