------------ Pobieranie stringów z pliku xml ------------
// Get a string resource from your app's Resources
String hello = getResources().getString(R.string.hello_world);

// Or supply a string resource to a method that requires a string
TextView textView = new TextView(this);
textView.setText(R.string.hello_world);



------------ Różne języki ------------
MyProject/
    res/
       values/
           strings.xml
       values-es/
           strings.xml
       values-fr/
           strings.xml




------------ Różne rozdzielczości ------------
MyProject/
    res/
        layout/              # default (portrait)
            main.xml
        layout-land/         # landscape
            main.xml
        layout-large/        # large (portrait)
            main.xml
        layout-large-land/   # large landscape
            main.xml



------------ Współczynniki przeliczania zdjęć dla różnych rozdzielczości ------------
•	xhdpi: 2.0
•	hdpi: 1.5
•	mdpi: 1.0 (baseline)
•	ldpi: 0.75

This means that if you generate a 200x200 image for xhdpi devices, you should generate the same resource in 150x150 for hdpi, 100x100 for mdpi, and 75x75 for ldpi devices.

Then, place the files in the appropriate drawable resource directory:
•	MyProject/
•	    res/
•	        drawable-xhdpi/
•	            awesomeimage.png
•	        drawable-hdpi/
•	            awesomeimage.png
•	        drawable-mdpi/
•	            awesomeimage.png
•	        drawable-ldpi/
•	            awesomeimage.png


------------ Adapter – czyli przesyłanie z danych (tablica stringów) na OnCreateView (adapter is used to populate a ListView) ------------
Parametry – Context, ID of list item layout, ID of text view, list of data
Context – pozwala na dostęp do system resources i services itd., posiada globalne iformacje na temat środowiska aplikacji

- Wywołujemy getActivity aby uzyskać dostęp do activity
ID of list item layout – podajemy layout na którym mają być wyświetlane informacje (R.layout.list_item_forecast)
ID of text view – podajemy id text view (R.id.list_item_forecast_textview) dokładne ID jakiegoś text view
List of data – lista danych (lista stringów zrobiona z tablicy stringów)


------------ Odnajdywanie Views – XML Layout -> View Hierarchy -> Java Code ------------
Button b = (Button) this.findViewById(R.id.btn);
LinearLayout container = (LinearLayout) this.findViewById(R.id.container);


------------ Przypisanie Adaptera do ListView ------------
	mForecastAdapter =
			new ArrayAdapter<String>(
					// The current context (this fragment's parent)
					getActivity(),
					// ID of list item layout
					R.layout.list_item_forecast,
					// ID of the textview to populate
					R.id.list_item_forecast_textview,
					// Forecast data
					weekForecast);

	// Get a reference to the ListView, and attach this adapter to
	ListView listView = (ListView) rootView.findViewById(
			R.id.listview_forecast);
	listView.setAdapter(mForecastAdapter);

	return rootView;

For an Activity
We inflate the layout and associate it with the Activity by calling the setContentView method in onCreate in our Activity:

setContentView(R.layout.activity_main);

For a Fragment
In our Fragment classes we inflate the layout in the onCreateView method, which includes a LayoutInflater as a parameter:

View rootView = inflater.inflate(R.layout.fragment_main, container, false);

The root view, or view element which contains all the other views, is returned by the inflate method of the LayoutInflater. We then should return this rootView for the onCreateView.


------------ Nawiązanie połączenia URL z danymi o stanie pogody JSON ------------
// These two need to be declared outside the try/catch
// so that they can be closed in the finally block.
HttpURLConnection urlConnection = null;
BufferedReader reader = null;

// Will contain the raw JSON response as a string.
String forecastJsonStr = null;
try {
// Construct the URL for the OpenWeatherMap query
// Possible parameters are avaiable at OWM's forecast API page, at
// http://openweathermap.org/API#forecast
URL url = new URL("http://api.openweathermap.org/data/2.5/forecast/daily?q=94043&mode=json&units=metric&cnt=7");

// Create the request to OpenWeatherMap, and open the connection
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();

// Read the input stream into a String
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
	// Nothing to do.
	return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));

String line;
while ((line = reader.readLine()) != null) {
	// Since it's JSON, adding a newline isn't necessary (it won't affect parsing)
	// But it does make debugging a *lot* easier if you print out the completed
	// buffer for debugging.
	buffer.append(line + "\n");
}

if (buffer.length() == 0) {
	// Stream was empty.  No point in parsing.
	return null;
}
forecastJsonStr = buffer.toString();
} catch (IOException e) {
	Log.e("PlaceholderFragment", "Error ", e);
// If the code didn't successfully get the weather data, there's no point in attemping to parse it.
return null;
} finally{
	if (urlConnection != null) {
		urlConnection.disconnect();
	}
	if (reader != null) {
		try {
		reader.close();
} catch (final IOException e) {
Log.e("PlaceholderFragment", "Error closing stream", e);
		}
	}
}
return rootView;
} } }

Any reason why you are using StringBuffer instead of StringBuilder?
Also, nitpicking: the creation of the buffer could be better placed on line 28 instead of 22, because the buffer is needed only after checking that the input stream is not null.


------------ Są dwa rodzaje połączeń w Androidzie (dwie klasy) ------------
HttpUrlConnection oraz HttpClient – polecany to HttpUrlConnection

Logi informacyjne
Error, Warn, Info, Debug, Verbose
Log.e(String tag, String msg), Log.w(‘’,’’), Log.i(), Log.d(), Log.v()

MyOpenWeatherMapApiKey = „b2825dac52ff0d6415eb76a1a2bad2a5;