how can I update onprogressupdate in asynctask using ExecutorService and Future Interface

[Jorge Vazquez]

I've research a bit about speeding up the application I'm working on. It is a network/port scanner and originally it did everything on a single thread using Asynctask. But I wanted to speed it up. So I looked at Runnable and Callable interface. Since I need to return something from the thread (if there's another way please let me know) I settled for Callable interface. My problem is that I can't figure out how to get the results from the Callable class and update the Asynctask onProgressUpdate() method. The IpScanCallable class returns data of type Node. Which is an object that holds information about especific node eg: ip, mac. I tried publishUpdate(node) but that didn't work. Is there any way of achieving this. Thanks
AsyncTask is at the buttom

package com.example.android.droidscanner;

    /*
    * AscynTask to scan the network
    * you should try different timeout for your network/devices
    * it will try to detect localhost ip addres and subnet. then
    * it will use subnet to scan network
    */
    private class TaskScanNetwork extends AsyncTask<Void, Node, Void> {
        static final int SCAN_THREADS = 8;
        static final int numOfHost = 254;
        String subnet = ip.substring(0, ip.lastIndexOf("."));;
        int startIp = 1;
        int endIp = startIp + SCAN_THREADS;
        static final int timeout = 1000;
        ExecutorService ipScanExecutor = Executors.newFixedThreadPool(SCAN_THREADS);
        List<Future<Node>> ipList = new ArrayList<>();

        @Override
        protected void onPreExecute() {
            Log.v("Ip Address: ", ip);
            hostList.clear();
            scanProgress.setMax(numOfHost);
            statusMsg.setText("Scanning " + subnet + ".0/24");
        }

        @Override
        protected Void doInBackground(Void... params) {
            for (int i = 0; i <= SCAN_THREADS; i++) {
                //if canceled terminate AsyncTask
                if(isCancelled()) {
                    break;
                }
                IpScanCallable ipScanCallable = new IpScanCallable(subnet, startIp, endIp);
                Future<Node> futureResults = ipScanExecutor.submit(ipScanCallable);
                startIp = endIp + 1;
                endIp = startIp + SCAN_THREADS;
                ipList.add(futureResults);
            }

            ipScanExecutor.shutdown();

            publishProgress();
            return null;
        }

        @Override
        protected void onProgressUpdate(Node... values) {
            //only add to ArrayList<Node> if host is alive on network
            if(values[0].ip != null) {
                hostList.add(values[0]);
                networkAdapter.notifyDataSetInvalidated();
                Toast.makeText(getApplicationContext(), values[0].getIp(), Toast.LENGTH_SHORT).show();
            }
            //update progress bar
            scanProgress.setProgress(values[0].progressBar);
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            statusMsg.setText(subnet + ".0/24 " + " Hosts");
        }
    }

}

IpScanCallable

package com.example.android.droidscanner;

import android.util.Log;

import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.concurrent.Callable;

/**
 * Created by jlvaz on 3/28/2017.
 */

public class IpScanCallable implements Callable<Node> {
    private Node newNode;
    private int timeout = 1000;
    private int progress;
    private String ip;
    private String network;
    private int startIp;
    private int endIp;

    public IpScanCallable(String network, int startIp, int endIp) {
        this.network = network;
        this.startIp = startIp;
        this.endIp = endIp;
    }

    @Override
    public Node call() throws Exception {
        for(int i = startIp; i <= endIp; i++) {
            ip = network + "." + i;
            Log.v("Host: ", ip);

            newNode = new Node();
            newNode.progressBar = i;

            try {
                InetAddress inetAddress = InetAddress.getByName(ip);
                if (inetAddress.isReachable(timeout)) {
                    newNode.ip = ip;
                }

            } catch (UnknownHostException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return newNode;
    }

}

[Tim Moores]

While you didn't say  what "that didn't work" means, exactly (please always TellTheDetails), what jumps out is that you're calling publishProgress with no parameters - so it can't possibly provide results. Either pass the Future to onProgressUpdate and handle it there, or remove the Callable/Future stuff entirely and run AsyncTask in parallel via executeOnExecutor().

As an aside, I took the liberty of removing the GUI code, since that doesn't have anything to do with the problem at hand.