Android Studio：无法从另一个类获取返回字符串

Question

I know it's kind of stupid question, but it's been a long time since I programmed Java in Android Studio. So actually I have the problem that I can't get a return from a class to another. I tried different kind of solutions suggested here, but none of them worked. Not sure why. I'm getting nothing displayed TextView in xml.

Here is the MainActivity.java:

public class MainActivity extends ActionBarActivity {
TextView txt_temp;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    XMLreference();
    StringRequest();
}

public void XMLreference(){
    txt_temp = (TextView) findViewById(R.id.txt_temp);
}

public void StringRequest(){
    WebServiceRequest webService = new WebServiceRequest();
    String request = webService.main();

    txt_temp.setText(request);
}

}

And here is the WebServiceRequest.java:

public class WebServiceRequest {
    private static final String username = "*********"; // put your Device Cloud username here
    private static final String password = "*********"; // put your Device Cloud password here
    public String responseContent;

    /**
     * Run the web service request
     */
    public String main() {
        HttpsURLConnection conn = null;

        try {
            // Create url to the Device Cloud server for a given web service request
            URL url = new URL("https://devicecloud.digi.com/ws/DataStream/00000000-00000000-********-********/xbee.serialIn");
            conn = (HttpsURLConnection) url.openConnection();
            conn.setDoOutput(true);
            conn.setDoInput(true);
            conn.setRequestMethod("GET");

            // Build authentication string
            String userpassword = username + ":" + password;

            // can change this to use a different base64 encoder
            String encodedAuthorization = Base64.encodeToString(userpassword.getBytes(), Base64.DEFAULT).trim();

            // set request headers
            conn.setRequestProperty("Authorization", "Basic "
                    + encodedAuthorization);

            InputStream is = conn.getInputStream();

            Scanner isScanner = new Scanner(is);
            StringBuffer buf = new StringBuffer();
            while (isScanner.hasNextLine()) {
                buf.append(isScanner.nextLine() + "\n");
            }
            responseContent = buf.toString();

            // add line returns between tags to make it a bit more readable
            responseContent = responseContent.replaceAll("><", ">\n<");

            // Output response to standard out
            // System.out.println(responseContent);

        } catch (Exception e) {
            // Print any exceptions that occur
            e.printStackTrace();
        } finally {
            if (conn != null)
                conn.disconnect();
        }
        return responseContent;
    }
}

I already tried to create

public void getResponseContent() {
    return responseContent;
}

And getting it with

WebServiceRequest webService = new WebServiceRequest();
String request = webService.getResponsteContent();

But it didn't work either. I'm not sure but I'm making somewhere a stupid mistake and after hours of programming I can't find the clue to solve it.

Answer 1

Okay I am not so sure if you want to have a constructor, but the main() never gets called so responseContent is always empty.

To match your code snipped

WebServiceRequest webService = new WebServiceRequest();
String request = webService.getResponsteContent();

Change your method main in WebServiceRequest to a constructor like this

public WebServiceRequest() { .. } // it was String main() before

It will get called as soon as you instantiate a WebServiceRequest

Answer 2

Web requests must be done from a second thread.

Runnable run = new Runnable() {
        @Override
        public void run() {
            try {
                //your main method here
                handler.post(new Runnable() {
                    @Override
                    public void run() {
                            //update your textView here
                    }

                });

            } catch (Exception e) {

            }
        }
    };
    Thread thread = new Thread(run);
    thread.start();

Also, you need to move the response code and update to the textView inside your web request method. Changes to the user interface must be posted to a handler.

Another option is to make your class extend IntentService. See here if you want to check that out.

https://developer.android.com/training/run-background-service/create-service.html