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strings.xml
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<resources>
    <string name="app_name">WeatherViewer</string>
    <string name="api_key">YOUR_API_KEY</string>
    <string name="web_service_url">http://api.openweathermap.org/data/2.5/forecast/daily?q=</string>
    <string name="invalid_url">Invalid URL</string>
    <string name="weather_condition_image">A graphical representation of the weather conditions</string>
    <string name="high_temp">High: %s</string>
    <string name="low_temp">Low: %s</string>
    <string name="day_description">%1$s: %2$s</string>
    <string name="humidity">Humidity: %s</string>
    <string name="hint_text">Enter city (e.g, Boston, MA, US)</string>
    <string name="read_error">Unable to read weather data</string>
    <string name="connect_error">Unable to connect to OpenWeatherMap.org</string>
</resources>


************************************************************************
Weather.java
************************************************************************
package at.htl.weatherviewer;

import java.text.NumberFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.TimeZone;

public class Weather {

    public final String dayOfWeek;
    public final String minTemp;
    public final String maxTemp;
    public final String humidity;
    public final String description;
    public final String iconURL;

    public Weather(long timeStamp, double minTemp, double maxTemp,
                   double humiditiy, String description, String iconName) {

        //NumberFormat to format double temperatures rounded to integers
        NumberFormat numberFormat = NumberFormat.getInstance()    ;
        numberFormat.setMaximumFractionDigits(0);

        this.dayOfWeek = convertTimeStampToDay(timeStamp);
        this.minTemp = numberFormat.format(minTemp) + "\u00B0C";
        this.maxTemp = numberFormat.format(maxTemp) + "\u00B0C";
        this.humidity = NumberFormat.getPercentInstance().format(humiditiy / 100.0);
        this.description = description;
        this.iconURL = "http://openweathermap.org/img/w/" + iconName + ".png";
    }

    // convert timestamp to a day's name (e.g. Monday, Tuesday, ..)
    private static String convertTimeStampToDay(long timeStamp) {
        Calendar calendar = Calendar.getInstance();
        calendar.setTimeInMillis(timeStamp * 1000);
        TimeZone tz = TimeZone.getDefault(); // get device's time zone

        // adjust time for device's time zone
        calendar.add(Calendar.MILLISECOND, tz.getOffset(calendar.getTimeInMillis()));

        // SimpleDateFormat that returns the day's name
        SimpleDateFormat dateFormatter = new SimpleDateFormat("EEEE");
        return dateFormatter.format(calendar.getTime());
    }
}







************************************************************************
WeatherArrayAdpter.java
************************************************************************

package at.htl.weatherviewer;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class WeatherArrayAdapter extends ArrayAdapter<Weather> {

    private static final String LOG_TAG = WeatherArrayAdapter.class.getSimpleName();

    // class for reusing views as list items scroll off and onto the screen
    private static class ViewHolder {
        ImageView conditionImageView;
        TextView dayTextView;
        TextView lowTextView;
        TextView hiTextView;
        TextView humidityTextView;
    }

    // stores already downloaded Bitmaps for reuse
    private Map<String, Bitmap> bitmaps = new HashMap<>();

    // constructor to initialize superclass inherited members
    public WeatherArrayAdapter(Context context, List<Weather> forecast) {
        super(context, -1, forecast);
    }

    // creates the custom view for the ListView's items
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View rowView = convertView;

        // get Weather object for this specified ListView position
        Weather day = getItem(position);

        ViewHolder viewHolder; // object that references's list item's views

        // check for reusable ViewHolder from ListView item that scrolled
        // offscreen; otherwise create a new ViewHolder
        if (rowView == null) {  // no reusable ViewHolder, so create one
            viewHolder = new ViewHolder();
            LayoutInflater inflater = LayoutInflater.from(getContext());
            rowView = inflater.inflate(R.layout.list_item, parent, false);
            viewHolder.conditionImageView =
                    (ImageView) rowView.findViewById(R.id.conditionImageView);
            viewHolder.dayTextView =
                    (TextView) rowView.findViewById(R.id.dayTextView);
            viewHolder.lowTextView =
                    (TextView) rowView.findViewById(R.id.lowTextView);
            viewHolder.hiTextView =
                    (TextView) rowView.findViewById(R.id.hiTextView);
            viewHolder.humidityTextView =
                    (TextView) rowView.findViewById(R.id.humidityTextView);
            rowView.setTag(viewHolder);  // assign the data to the item as a tag
        } else { // reuse existing ViewHolder stored as the list item's tag
            viewHolder = (ViewHolder) rowView.getTag();
        }

        // if weather condition icon already downloaded use it;
        // otherwise, download icon in a separate thread
        if (bitmaps.containsKey(day.iconURL)) {
            viewHolder.conditionImageView.setImageBitmap(bitmaps.get(day.iconURL));
        } else {
            // download and display weather condition image
            Log.d(LOG_TAG, "day.iconURL = " + day.iconURL);
            new LoadImageTask(viewHolder.conditionImageView).execute(day.iconURL);
        }

        // get other data from Weather object and place into views
        Context context = getContext(); // for loading String resources
        viewHolder.dayTextView.setText(context.getString(
                R.string.day_description, day.dayOfWeek, day.description));
        viewHolder.lowTextView.setText(
                context.getString(R.string.low_temp, day.minTemp));
        viewHolder.hiTextView.setText(
                context.getString(R.string.high_temp, day.maxTemp));
        viewHolder.humidityTextView.setText(
                context.getString(R.string.humidity, day.humidity));

        return rowView; // return completed list item to display
    }

    // AsyncTask to load weather conditions icons in a separate thread
    private class LoadImageTask extends AsyncTask<String, Void, Bitmap> {
        private ImageView imageView; // displays the thumbnail

        // store ImageView on which to set the download Bitmap
        public LoadImageTask(ImageView imageView) {
            this.imageView = imageView;
        }

        // load image: params[0] is the String URL representing the image
        @Override
        protected Bitmap doInBackground(String... params) {
            Bitmap bitmap = null;
            HttpURLConnection connection = null;

            try {
                URL url = new URL(params[0]); // create URL for image

                // open an HttpURLConnection, get its InputStream
                // and download the image
                connection = (HttpURLConnection) url.openConnection();

                try (InputStream inputStream = connection.getInputStream()) {
                    bitmap = BitmapFactory.decodeStream(inputStream);
                    bitmaps.put(params[0], bitmap); // cache for later use
                } catch (Exception e) {
                    e.printStackTrace();
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                connection.disconnect();
            }
            return bitmap;
        }

        // set weather condition image in list item
        @Override
        protected void onPostExecute(Bitmap bitmap) {
            imageView.setImageBitmap(bitmap);
        }
    }
}







************************************************************************
MainActivity.java
************************************************************************
package at.htl.weatherviewer;

import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.view.inputmethod.InputMethodManager;
import android.widget.AdapterView;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private static final String LOG_TAG = MainActivity.class.getSimpleName();

    // List of Weather objects representing the forecast
    private List<Weather> weatherList = new ArrayList<>();

    // ArrayAdapter for binding Weather objects to a ListView
    private WeatherArrayAdapter weatherArrayAdapter;
    private ListView weatherListView;

    // configure Toolbar, ListView and FAB
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // autogenerated code to inflate layout and configure Toolbar
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        // create ArrayAdapter to bind weatherList to the weatherListView
        weatherListView = (ListView) findViewById(R.id.weatherListView);
        weatherArrayAdapter = new WeatherArrayAdapter(this, weatherList);
        weatherListView.setAdapter(weatherArrayAdapter);

        weatherListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Toast.makeText(getBaseContext(), "Item clicked", Toast.LENGTH_SHORT).show();
                Snackbar.make(findViewById(R.id.coordinatorLayout), "item clicked", Snackbar.LENGTH_SHORT).show();
            }
        });

        // Configure FAB to hide keyboard and initiate web service request
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // get next from locationEditText and create web service URL
                EditText locationEditText = (EditText) findViewById(R.id.locationEditText);
                URL url = createURL(locationEditText.getText().toString());

                // hide keyboard and initiate a GetWeatherTask to download
                // weather data from OpenWeatherMap.org in a separate thread
                if (url != null) {
                    dismissKeyboard(locationEditText);
                    GetWeatherTask getLocalWeatherTask = new GetWeatherTask();
                    getLocalWeatherTask.execute(url);
                } else {
                    Snackbar.make(findViewById(R.id.coordinatorLayout),
                            R.string.invalid_url, Snackbar.LENGTH_LONG).show();
                }
            }
        });
    }

    private void dismissKeyboard(View view) {
        InputMethodManager imm =
                (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
        imm.hideSoftInputFromWindow(view.getWindowToken(), 0);
    }

    // create openweathermap.org web service URL using city
    private URL createURL(String city) {
        String apiKey = getString(R.string.api_key);
        String baseUrl = getString(R.string.web_service_url);

        try {
            // create URL for specified city and metric units (Celsius)
            String urlString = baseUrl + URLEncoder.encode(city, "UTF-8") +
                    "&units=metric&cnt=16&APPID=" + apiKey;
                    // "&units=metric&lang=de&cnt=16&APPID=" + apiKey; // deutsche Übersetzung
            return new URL(urlString);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return null; // URL was malformed

    }

    // makes the REST web service call to get weather data and
    // saves the data to a local HTML file
    private class GetWeatherTask extends AsyncTask<URL, Void, JSONObject> {

        private final String LOG_TAG = GetWeatherTask.class.getSimpleName();

        @Override
        protected JSONObject doInBackground(URL... params) {
            HttpURLConnection connection = null;

            try {
                connection = (HttpURLConnection) params[0].openConnection();
                int response = connection.getResponseCode();

                if (response == HttpURLConnection.HTTP_OK) {
                    StringBuilder builder = new StringBuilder();

                    try (BufferedReader reader = new BufferedReader(
                            new InputStreamReader(connection.getInputStream()))) {

                        String line;

                        while ((line = reader.readLine()) != null) {
                            builder.append(line);
                        }
                    } catch (IOException e) {
                        Snackbar.make(findViewById(R.id.coordinatorLayout),
                                R.string.read_error, Snackbar.LENGTH_LONG).show();
                        e.printStackTrace();
                    }

                    Log.d(LOG_TAG, builder.toString());
                    return new JSONObject(builder.toString());
                } else {
                    Snackbar.make(findViewById(R.id.coordinatorLayout),
                            R.string.connect_error, Snackbar.LENGTH_LONG).show();
                }
            } catch (Exception e) {
                Snackbar.make(findViewById(R.id.coordinatorLayout),
                        R.string.connect_error, Snackbar.LENGTH_LONG).show();
                e.printStackTrace();
            } finally {
                connection.disconnect(); // close the HttpURLConnection
            }

            return null;
        }

        // process JSON response and update ListView
        @Override
        protected void onPostExecute(JSONObject weather) {
            convertJSONtoArrayList(weather); // repopulate weatherList
            weatherArrayAdapter.notifyDataSetChanged(); // rebind to ListView
            weatherListView.smoothScrollToPosition(0); // scroll to top
        }
    }

    // create Weather objects from JSONObject containing the forecast
    private void convertJSONtoArrayList(JSONObject forecast) {
        weatherList.clear(); // clear old weather data

        try {
            // get forecast's "list" JSONArray
            JSONArray list = forecast.getJSONArray("list");

            // convert each element of list to a Weather object
            for (int i = 0; i < list.length(); ++i) {
                JSONObject day = list.getJSONObject(i); // get one day's data

                // get the day's temperatures ("temp") JSONObject
                JSONObject temperatures = day.getJSONObject("temp");

                // get day's "weather" JSONObject for the description and icon
                JSONObject weather =
                        day.getJSONArray("weather").getJSONObject(0);

                // add new Weather object to weatherList
                weatherList.add(new Weather(
                        day.getLong("dt"), // date/time timestamp
                        temperatures.getDouble("min"), // minimum temperature
                        temperatures.getDouble("max"), // maximum temperature
                        day.getDouble("humidity"), // percent humidity
                        weather.getString("description"), // weather conditions
                        weather.getString("icon"))); // icon name
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

}






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