当工作线程在android中完成其工作时如何从工作线程向主线程获取通知

Question

This is my code.

public class MainActivity extends AppCompatActivity {

    private ListView listView;

    // URL to get contacts JSON
    private static String url = "example.com";

    // JSON Node names
    private static final String TAG_DEVICES = "devices";
    private static final String TAG_TYPE = "type";
    private static final String TAG_NAME = "name";
    private static final String TAG_MODEL = "model";

    // contacts JSONArray
    JSONArray devices = null;
    String jsonStr= null;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.devices);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        /*
        List<Device> devices = new ArrayList<>();

        Device device1 = new Device("tv", "la22c450e1", "samsung");
        Device device2 = new Device("washing machine", "lg34gfer", "lg");
        Device device3 = new Device("monitor", "dlrtio78", "dell");
        Device device4 = new Device("tv", "sie45vgt", "sansui");
        devices.add(device1);
        devices.add(device2);
        devices.add(device3);
        devices.add(device4);
    */


        List<Device> deviceList = new ArrayList<>();
        String jsonStr = null;

        startProgress(url);

        // ONCE GET NOTIFICATION FROM THREAD then run this code.

        if (jsonStr != null) {
            try {
                JSONObject jsonObj = new JSONObject(jsonStr);

                // Getting JSON Array node
                devices = jsonObj.getJSONArray(TAG_DEVICES);

                // looping through All Contacts
                for (int i = 0; i < devices.length(); i++) {
                    JSONObject c = devices.getJSONObject(i);
                    String name = c.getString(TAG_NAME);
                    String model = c.getString(TAG_MODEL);
                    String type = c.getString(TAG_TYPE);
                    Device device = new Device(type, model, name);

                    // adding device to device list
                    deviceList.add(device);

                }
                DeviceAdapter adapter = new DeviceAdapter(getApplicationContext(), deviceList);
                listView.setAdapter(adapter);


            } catch (JSONException e) {
                e.printStackTrace();
            }
        } else {
            Log.e("ServiceHandler", "Couldn't get any data from the url");
        }
    }

    private void startProgress(final String url) {
        // do something long
        Runnable runnable = new Runnable() {
            @Override
            public void run() {

                try{
                    jsonStr = FetchData(url);
                }
                catch(IOException ie) {
                    ie.printStackTrace();
                }


            }
        };
        new Thread(runnable).start();
    }

    private String FetchData(String url) throws IOException {
        URL obj = new URL(url);
        StringBuffer stringBuffer = null;
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();
        con.setRequestMethod("GET");
        //con.setRequestProperty("User-Agent", USER_AGENT);
        int responseCode = con.getResponseCode();
        System.out.println("GET Response Code :: " + responseCode);
        if (responseCode == HttpURLConnection.HTTP_OK) { // success
            BufferedReader in = new BufferedReader(new InputStreamReader(
                    con.getInputStream()));
            String inputLine;
            stringBuffer = new StringBuffer();

            while ((inputLine = in.readLine()) != null) {
                stringBuffer.append(inputLine);
            }
            in.close();

            // print result
            System.out.println(stringBuffer.toString());
        } else {
            System.out.println("GET request not worked");
        }


        return stringBuffer.toString();

    }
}

How should i get notification here (// ONCE GET NOTIFICATION FROM THREAD then run this code.) from worker thread to execute the code only after notification?

Edit : I understand AsyncTask can make my life easy. But because of requirement description i can not use AsyncTask. So please suggest me best alternative for AsyncTask.

Answer 1

This doesn't make any sense:

startProgress(url);
// ONCE GET NOTIFICATION FROM THREAD then run this code.
...

I'm assuming that "once get notification from thread" is supposed to mean wait for the other thread.

It never makes any sense to start a new thread, and then immediately wait for it to complete. The whole point of multi-threading is that two (or more) threads can be doing different things at the same time .

A simple use-case for multi-threading looks like this:

startBackgroundThread(...);
doSomethingElseWhileBackgroundThreadIsRunning(...);
waitForResultFromBackgroundThread(...);

If you're not going to do something else while the background thread is running, then you'd be better off simplifying the program and doing all of the work in one thread.

---

PS, if you want to communicate a single result from a background task to a foreground thread, you might try using a java.util.concurrent.SynchronousQueue instance.