AsyncTask Android - Design Pattern and Return Values

Question

I\'m writing an application that validates login credentials on an external webserver - so I have the basic issue of creating a login screen that when submitted will send an

Answer 1

suppose the data format with web api is json, my design pattern :

common classes
1.MyAsyncTask : extends AsyncTask
2.BackgroundBase : parameters to server
3.API_Base : parameters from server
4.MyTaskCompleted : callback interface

public class MyAsyncTask extends AsyncTask {
    private ProgressDialog pd ; 
    private MyTaskCompleted listener;
    private Context cxt;
    private Class resultType;
    private String url;
    private int requestCode;    

    public MyAsyncTask(MyTaskCompleted listener, Class resultType, int requestCode, String url){
        this.listener = listener;
        this.cxt = (Context)listener;
        this.requestCode = requestCode;
        this.resultType = resultType;
        this.url = url;
    }
    public MyAsyncTask(MyTaskCompleted listener, Class resultType, int requestCode, String url, ProgressDialog pd){
            this(listener, resultType, requestCode, url);
            this.pd = pd;
            this.pd.show();
    }   

    @Override
    protected APIClass doInBackground(BackgroundClass... params) {
        APIClass result = null;
        try {           
            //do something with url and params, and get data from WebServer api
            BackgroundClass oParams = params[0];
            String sUrl = url + "?d=" + URLEncoder.encode(oParams.getJSON(), "UTF-8");
            String source = "{\"RtnCode\":1, \"ResultA\":\"result aaa\", \"ResultB\":\"result bbb\"}";

            //to see progressdialog
            Thread.sleep(2000);

            result = new com.google.gson.Gson().fromJson(source, resultType);           
        } catch (Exception e) {
            e.printStackTrace();
        }

        return result;
    }

     @Override
     protected void onPostExecute(APIClass result) {
        super.onPostExecute(result);

        try {
            if(pd != null && pd.isShowing())
                pd.dismiss();

            API_Base oApi_Base = (API_Base)result;          
            listener.onMyTaskCompleted(result , this.requestCode);                      
        } catch (Exception e) {
            e.printStackTrace();
        }           
    }

}
public class API_Base {
    public int RtnCode;

    public String getJSON(Context context) throws Exception
    {
        return new com.google.gson.Gson().toJson(this);
    }


    public String toString(){
        StringBuilder sb = new StringBuilder();

        for (Field field : this.getClass().getFields()) {
            try {
                field.setAccessible(true); 
                Object value = field.get(this); 
                if (value != null) {
                    sb.append(String.format("%s = %s\n", field.getName(), value));
                }
            } catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
            }

        }

        return sb.toString();
    }

}
public class BackgroundBase {

    public String getJSON() throws Exception
    {       
        return new com.google.gson.Gson().toJson(this);
    }

}
public interface MyTaskCompleted {
    void onMyTaskCompleted(API_Base oApi_Base, int requestCode) ;
}

example, let's call two api in one activity
assume :
API 1.http://www.google.com/action/a
input params : ActionA
output params : RtnCode, ResultA

API 2.http://www.google.com/action/b
input params : ActionB
output params : RtnCode, ResultB

classes with example :
1.MyActivity : extends Activity and implements MyTaskCompleted
2.MyConfig : utility class, i set requestCode here
3.BackgroundActionA, BackgroundActionB : model classes for api's input params
4.API_ActionA, API_ActionB : model classes for api's output params

public class MyActivity extends Activity implements MyTaskCompleted {
    ProgressDialog pd;
    Button btnActionA, btnActionB;
    TextView txtResult;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_layout);
        btnActionA = (Button)findViewById(R.id.btn_actionA);
        btnActionB = (Button)findViewById(R.id.btn_actionB);
        txtResult = (TextView)findViewById(R.id.txt_result);

        btnActionA.setOnClickListener(listener_ActionA);
        btnActionB.setOnClickListener(listener_ActionB);

        pd = new ProgressDialog(MyActivity.this);
        pd.setTitle("Title");
        pd.setMessage("Loading");
    }

    Button.OnClickListener listener_ActionA = new Button.OnClickListener(){

        @Override
        public void onClick(View v) {
            //without ProgressDialog
            BackgroundActionA oBackgroundActionA = new BackgroundActionA("AAA");
            new MyAsyncTask(MyActivity.this, 
                                                            API_ActionA.class, 
                                                            MyConfig.RequestCode_actionA,
                                                            "http://www.google.com/action/a").execute(oBackgroundActionA);
        }

    };
    Button.OnClickListener listener_ActionB = new Button.OnClickListener(){

        @Override
        public void onClick(View v) {
            //has ProgressDialog
            BackgroundActionB oBackgroundActionB = new BackgroundActionB("BBB");
            new MyAsyncTask(MyActivity.this, 
                                                            API_ActionB.class, 
                                                            MyConfig.RequestCode_actionB,
                                                            "http://www.google.com/action/b",
                                                            MyActivity.this.pd).execute(oBackgroundActionB);
        }

    };

    @Override
    public void onMyTaskCompleted(API_Base oApi_Base, int requestCode) {
        // TODO Auto-generated method stub
        if(requestCode == MyConfig.RequestCode_actionA){
            API_ActionA oAPI_ActionA = (API_ActionA)oApi_Base;
            txtResult.setText(oAPI_ActionA.toString());

        }else if(requestCode == MyConfig.RequestCode_actionB){
            API_ActionB oAPI_ActionB = (API_ActionB)oApi_Base;
            txtResult.setText(oAPI_ActionB.toString());

        }

    }

}
public class MyConfig {
    public static String LogTag = "henrytest";

    public static int RequestCode_actionA = 1001;
    public static int RequestCode_actionB = 1002;
}
public class BackgroundActionA extends BackgroundBase {
    public String ActionA ;

    public BackgroundActionA(String actionA){
        this.ActionA = actionA;
    }

}
public class BackgroundActionB extends BackgroundBase {
    public String ActionB;

    public BackgroundActionB(String actionB){
        this.ActionB = actionB;
    }
}
public class API_ActionA extends API_Base {
    public String ResultA;
}
public class API_ActionB extends API_Base {
    public String ResultB;
}

Advantage with this design pattern :
1.one Advantage for multi api
2.just add model classes for new api, ex: BackgroundActionA and API_ActionA
3.determine which API by different requestCode in callback function : onMyTaskCompleted