Display an XML on main thread

Question

I have a little issue about a little thing I don't understand.

It's just a simple request: how do I display an xml I just got in a thread?

There is my method postData to get the xml, I make it display in a log.v as you can see below in the code, but I can't display it to a TextView out of the thread.

public class RecupXml_Activity extends Activity {

TextView campagne;
String user = "toto";
String password = "tata";
String theCampagneXml;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fragment_main);

    campagne = (TextView) findViewById(R.id.campagneTest);

    postData(user, password);

}

public void postData(final String login, final String password) {

    Thread background = new Thread(new Runnable() {
        URL url;
        String buffer;
        String theCampagneXml = null;

        @Override
        public void run() {
            try {

                URLConnection urlConnection;

                String body = "login=" + URLEncoder.encode(login, "UTF-8") + "&password=" + URLEncoder.encode(password, "UTF-8");

                url = new URL("http://3pi.tf/apps/sms/");
                urlConnection = url.openConnection();

                ((HttpURLConnection) urlConnection).setRequestMethod("POST");

                urlConnection.setDoOutput(true);
                urlConnection.setDoInput(true);
                urlConnection.setUseCaches(false);
                urlConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
                urlConnection.setRequestProperty("Content-Length", "" + body.length());

                OutputStreamWriter writer = null;
                BufferedReader reader = null;
                writer = new OutputStreamWriter(urlConnection.getOutputStream());

                writer.write(body);
                writer.flush();

                reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
                while ((buffer = reader.readLine()) != null) {
                    theCampagneXml = buffer;
                }
                Log.v("test", "xml = " + theCampagneXml);

            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
            } catch (IOException e) {
                // TODO Auto-generated catch block
            }

            campagne.post(new Runnable() {

                @Override
                public void run() {
                    campagne.setText("salut voici ta campagne : " + theCampagneXml);

                }
            });

        }

    });
    background.start();
}

}

It appears in my Log but not in the TextView:/ I have a white empty Activity.

Answer 1

The problem is that you call postData() on UI-tread, meaning that the method also returns theCampagneXml on UI-thread, while your network operation goes on a worker thread. The following code with some changes and additions fixes the problem:

public class MainActivity extends Activity  {

    TextView campagne;
    String user = "toto";
    String password = "tata";
    String theCampagneXml; // new

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        campagne = (TextView) findViewById(R.id.text);
        postData(user, password); // new
    }

public void postData(final String login, final String password) { // note: the return type has been changed

Thread background = new Thread(new Runnable() {
    URL url;
    String buffer;
    String theCampagneXml = null; // new

    @Override
    public void run() {
        try {
            // no changes here but declaring `theCampagneXml` as class member
        }
        campagne.post(new Runnable() {

            @Override
            public void run() {
                campagne.setText("hello, here is your XML : "+ theCampagneXml);
            }
        });
    }
});

background.start();
}
}

Once the network operation is done and theCampagneXml is initialized, use post() for the TextView campagne that runs on UI-thread.

Additional info can be found in Processes and Threads.