使用asynctask从套接字返回对象

Question

I am trying to save a Collection which I get through a socket connection. I use AsyncTask to read the message from socket that has the Collection. My problem is that I cannot save this message. In OnpostExecute() the Log.d() messages are not being displayed. If I do ReceiveMsgAsyncTask().execute().get() the UI freezes. I have read many similar issues but I cannot find a solution. How can I save the message received from my socket?Thanks in advance..

private class ReceiveMsgAsyncTask extends AsyncTask<Object, Void, Object> {
    final Collection <String> col = new ArrayList<String>();
    Socket socket = null ;
    ObjectInputStream in = null;
    @Override
    protected Object doInBackground(Object... arg0) {
        // TODO Auto-generated method stub;
        Object msg = null;
         try {
                socket = new Socket(host,50000);
                in = new ObjectInputStream(socket.getInputStream());
                msg = in.readObject();
            } catch (UnknownHostException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }finally {
                try {
                    in.close();
                    socket.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        return msg;
    }

    protected void onPostExecute(Object result) {
        // TODO Auto-generated method stub
        Log.d("mesg","success");
        super.onPostExecute(result);
        col.addAll((Collection<?extends String>)result);
    }

Here is the Server's method that sends the Collection to client

public void splitData(Master master,String client){
        int chunk=0;
        int chunckStart=0;
            BufferedReader br = null;
            ObjectOutputStream out = null;
            try {
                String sCurrentLine;
                br = new BufferedReader(new FileReader("input"));
                int numberOflines=0;
                while ((sCurrentLine = br.readLine()) != null) {
                    numberOflines++;
                }
                br.close();
                br = new BufferedReader(new FileReader("input"));
                for (int i=1;i<=master.numberOfWorkers;i++){
                    out = new ObjectOutputStream(incoming.getOutputStream());
                    Worker Mworker = new Worker(clientsList.get(i-1));
                    if (i==master.numberOfWorkers){
                        if (numberOflines%master.numberOfWorkers!=0)
                            chunk = ((numberOflines/master.numberOfWorkers)*i)+numberOflines%master.numberOfWorkers;
                        else chunk = ((numberOflines/master.numberOfWorkers)*i);
                    }
                    else chunk = ((numberOflines/master.numberOfWorkers)*i);
                    int counter = chunk;
                    while (counter>chunckStart) {
                        sCurrentLine = br.readLine();
                        System.out.println(sCurrentLine);
                        //Mworker.reduce(sCurrentLine, 1);
                        Mworker.getCollection().add(sCurrentLine);
                        counter--;
                    }
                    System.out.println("----------------------------------");
                    chunckStart = chunckStart +(numberOflines/master.numberOfWorkers);
                    System.out.println(Mworker.getWorkerName()+" has the list:");
                    //System.out.println(Mworker.getHashReduce());
                    System.out.println(Mworker.getCollection());
                    out.writeObject(Mworker.getCollection());//send chunk to the worker/client
                    //out.flush();
                    //out.close();
                }

            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (br != null) br.close();
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
            //Mworker.hashReduce
        //}
    }

Answer 1

I am guessing that your Worker class does not implement Serialializable

See Javadoc

Only objects that support the java.io.Serializable interface can be written to streams.

Answer 2

please look at the document for AsyncTask.get() it clearly states

Waits if necessary for the computation to complete, and then retrieves its result.

Therefore calling 'get' negates the whole reason to use an asynctask.

What you need to do is:

1. Create an interface with a call back method.
2. make your activity or fragment implement that interface.
3. make your ReceiveMsgAsyncTask take an object implementing that interface on it's constructor.
4. in the onPostExecute of ReceiveMsgAsyncTask call the callback method passing your results into it.

Now common pitfall here is what happens if the activity is closed or otherwise rendered defunct. This can cause crashes and all kinds of other weirdness.

The easiest way to solve that issue is to keep copies of any outstanding asynctasks and cancel then in your activities or fragments onPause methods.