sample activity in android

package com.example.android.sunshine;

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.TextView;

import com.example.android.sunshine.data.SunshinePreferences;
import com.example.android.sunshine.utilities.NetworkUtils;
import com.example.android.sunshine.utilities.OpenWeatherJsonUtils;

import java.net.URL;

public class MainActivity extends AppCompatActivity {

    private TextView mWeatherTextView;

    // TODO (6) Add a TextView variable for the error message display    private TextView errorTextView;

    // TODO (16) Add a ProgressBar variable to show and hide the progress bar    private ProgressBar progressBar;

    @Override    

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_forecast);

        /*        

         * Using findViewById, we get a reference to our TextView from xml. This allows us to         

         * do things like set the text of the TextView. */ 

        mWeatherTextView = (TextView) findViewById(R.id.tv_weather_data);

        // TODO (7) Find the TextView for the error message using findViewById        

        errorTextView = (TextView) findViewById(R.id.errorTextView);

        // TODO (17) Find the ProgressBar using findViewById      

        progressBar = (ProgressBar) findViewById(R.id.loadingProgressBar);

        /* Once all of our views are setup, we can load the weather data. */        

        loadWeatherData();
    }

     /**      

       * This method will get the user's preferred location for weather, and then tell some     

       * background method to get the weather data in the background.     */    

    private void loadWeatherData() {
        // TODO (20) Call showWeatherDataView before executing the AsyncTask        

        showWeatherDataView();

        String location = SunshinePreferences.getPreferredWeatherLocation(this);
        new FetchWeatherTask().execute(location);
    }

    // TODO (8) Create a method called showWeatherDataView that will hide the error message and show the weather data    

    private void showWeatherDataView(){
        errorTextView.setVisibility(View.INVISIBLE);
        mWeatherTextView.setVisibility(View.VISIBLE);
    }

    // TODO (9) Create a method called showErrorMessage that will hide the weather data and show the error message    

    private void showErrorMessage(){
        mWeatherTextView.setVisibility(View.INVISIBLE);
        errorTextView.setVisibility(View.VISIBLE);
    }

    public class FetchWeatherTask extends AsyncTask<String, Void, String[]> {

        // TODO (18) Within your AsyncTask, override the method onPreExecute and show the loading indicator        

        @Override        

        protected void onPreExecute() {
            progressBar.setVisibility(View.VISIBLE);
        }

        @Override       

        protected String[] doInBackground(String... params) {

            /* If there's no zip code, there's nothing to look up. */  

            if (params.length == 0) {
                return null;
            }

            String location = params[0];
            URL weatherRequestUrl = NetworkUtils.buildUrl(location);

            try {
                String jsonWeatherResponse = NetworkUtils
                        .getResponseFromHttpUrl(weatherRequestUrl);

                String[] simpleJsonWeatherData = OpenWeatherJsonUtils
                        .getSimpleWeatherStringsFromJson(MainActivity.this, jsonWeatherResponse);

                return simpleJsonWeatherData;

            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }
        }

        @Override        

        protected void onPostExecute(String[] weatherData) {
            // TODO (19) As soon as the data is finished loading, hide the loading indicator           

            progressBar.setVisibility(View.INVISIBLE);

            if (weatherData != null) {
                // TODO (11) If the weather data was not null, make sure the data view is visible                

                 showWeatherDataView();
                /*                

                 * Iterate through the array and append the Strings to the TextView. The reason why we add                 

                 * the "\n\n\n" after the String is to give visual separation between each String in the                 

                 * TextView. Later, we'll learn about a better way to display lists of data.*/               

                for (String weatherString : weatherData) {

                    mWeatherTextView.append((weatherString) + "\n\n\n");
                }
            }
            // TODO (10) If the weather data was null, show the error message            

           if(weatherData == null){
                showErrorMessage();
            }

        }
    }

    @Override    public boolean onCreateOptionsMenu(Menu menu) {
        /* Use AppCompatActivity's method getMenuInflater to get a handle on the menu inflater */        

        MenuInflater inflater = getMenuInflater();
        /* Use the inflater's inflate method to inflate our menu layout to this menu */        

        inflater.inflate(R.menu.forecast, menu);
        /* Return true so that the menu is displayed in the Toolbar */        

        return true;
    }

    @Override    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.action_refresh) {
            mWeatherTextView.setText("");
            loadWeatherData();
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}