1. USING ANDROID WITH THE INTERNET

2. Slide 2 Network Prerequisites The following must be included so as to allow the device to connect to the network The tag should be an immediate child of

3. Slide 3 HTTP (Introduction) In most cases the transfer protocol is HTTP We connect our device to a server and get data We then process that data somehow Two HTTP clients HttpClient HttpURLConnection Both support HTTPS and IPV6 Use HttpURLConnection for post Lollypop devices

4. Slide 4 Checking for Network Access The network might be unavailable for many reasons We may have WiFi service or just cell service Note that service might be metered so we need to limit bandwidth

5. Slide 5 The ConnectivityManager The ConnectivityManager answers questions about the state of the network The getSystemService( Context.CONNECTIVITY_SERVICE) method gets an instance of the class

6. Slide 6 The NetworkInfo Class The getActiveNetworkInfo class returns an NetworkInfo instance Call the isConnected method to determine whether there is a network connection See http://developer.android.com/reference/android /net/NetworkInfo.html

7. Slide 7 Introduction to Multithreading Many activities can take a while to complete Some activities might not complete at all A thread is a concurrent unit of execution There is a thread for the UI We can create other threads This is a complicated topic but I’ll provide just enough here for you to create a thread and run it

8. Slide 8 The AsyncTask Class (Introduction) The android.os.AsyncTask allows background operations to be performed and returned to the UI thread It is a helper class that wraps the Thread class Use it to perform short-lived background tasks Params, Progress, Result

9. Slide 9 The AsyncTask Class (Creating) To use the AsyncTask create a subclass with three generic parameters The first contains the data passed to the thread The second, if used contains an integer used to report the thread’s progress The third, if used contains the data type of the thread value. If the parameter is Void, then it will not be used

10. Slide 10 The AsyncTask Class (Example) Extend AsyncTask A string is passed to the task There is no progress reporting A string is returned from the task When the background task is executed, it goes through four steps

11. Slide 11 The AsyncTask Class (Implementing – Step 1) onPreExecute is invoked on the UI thread before the task begins It is here that you setup the task Initialize a progress meter, for example Implementing this step is optional

12. Slide 12 The AsyncTask Class (Implementing – Step 2) doInBackground is the worker It executes immediately after onPreExecute finishes It is here that you perform the background computation The parameters are passed to this procedure The results are returned in this step Call publishProgress(Progress…) to publish progress results (optional)

13. Slide 13 The AsyncTask Class (Implementing – Step 2) String … denotes a variable length array of type String So urls contains the parameters

14. Slide 14 The AsyncTask Class (Implementing – Step 3) onProgressUpdate is invoked on the UI thread It gets called as a result of the publishProgress call Use it to update a progress meter or log Implementing this method is optional

15. Slide 15 The AsyncTask Class (Implementing – Step 4) onPostExecute is invoked on the UI thread The parameter contains the result of the asynchronous method call

16. Slide 16 STATUS You now know how to set up the asynchronous infrastructure Net we will see how to send a HTTP request with a URL and process the result

17. Slide 17 Android URL and HTTP Related Classes The URL class

18. Slide 18 The URL Class The java.net.URL class represents a url Convert strings to URLs Convert URLs to strings http://developer.android.com/reference/java/ net/URL.html http://developer.android.com/reference/java/ net/URL.html

19. Slide 19 The URL Class

20. Slide 20 Opening a Connection (1) The URL.openConnectcion() method establishes a connection to a resource Over this connection, you make the request and get the response We will use HTTP here but other protocols are supported

21. Slide 21 Opening a Connection (2) The setReadTimeout setter defines the time to wait for data The setConnectTimeout setter the time to wait before establishing a connection The setRequestMethod defines whether the request will be a GET or a POST The setDoInput setter, if true allows receiving of data

22. Slide 22 Opening a Connection (3) Calling the connect() method opens the connection getResponseCode() gets the HTTP response code from the server -1 if there is no response code. Such as 404 not found? getInputStream() gets the input stream from which you can read data Works just like an open file

23. Slide 23 Opening A Connection (Example)

24. Slide 24 Reading the Input

25. Slide 25 Introduction to XML XML is briefly discussed here as it provides a generalized means to get URL data Many services return data as XML

26. Slide 26 What XML Does Nothing

27. Slide 27 What XML is Philosophically (1) It’s a language designed to describe data in a hierarchical way By itself, XML is useless XML does not process the data it describes Simply put, XML elements are collected together into an XML document It’s up to “something else” to process that document

28. Slide 28 What XML is Philosophically (2) Hierarchical XML data can represent anything Even though XML does nothing with the data That’s because XML describes data XML does not describe the meaning of data There are other XML “recommendations” that give meaning to XML data

29. Slide 29 A First XML Example The answer (question) to the universe is 42 42

30. Slide 30 How XML Works (1) An XML document is processed using a generic XML parser Companies that support XML have an implementation of an XML parser The XML Document Object Model (DOM) represents an XML document in-memory Again, this representation is defined by the W3C.NET supports the “level 2” DOM representation

31. Slide 31 How XML Works (2) An XML parser processes hierarchical XML data, which is made up of: markup – Tags, references, and declarations, which are processed by the XML parser character data – Data appearing between the markup Character data is not processed by the XML parser It’s the document’s data

32. Slide 32 XML Documents (Introduction) XML syntax is simple but rigorous An XML document must be syntactically correct to be well formed As opposed to HTML document which can be processed even though the are incorrect An XML document must adhere to the rules set for by a DTD or XSD to be valid Formally, an XML document is an instance of a class defined by the DTD or XSD More on this topic later when we get to document validation

33. Slide 33 Introduction to XML Syntax (1) XML tags resemble HTML tags but they are not predefined That is, you give names to tags just as you give names to variables and other identifiers Starting tags appear as Ending tags appear as Empty elements can appear as XML elements MUST have an ending tag unlike HTML A starting and ending tag makes up an element

34. Slide 34 Introduction to XML Syntax (2) An element can have different types of content If an element contains other elements, it has element content If an element contains text and other elements, the element has mixed content If an element contains only data, then the element has simple content Elements can also have 0, 1 or more attributes

35. Slide 35 Introduction to XML Syntax (3) Tags can be nested These are hierarchical nodes Tags MUST be nested correctly though There must be only one root tag White space is preserved in XML documents This is a big departure from HTML A new line is represented with the LF character Space and Tab characters are also considered white space

36. Slide 36 XML Attributes (Introduction) Tags can have one or more attributes Attributes appear after the tag name Attributes are conceptually similar to properties An attribute could also be implemented as a nested element The choice is yours As you will see, a schema restricts and attribute’s values or occurrences

37. Slide 37 XML Attributes (Syntax 1) Attributes appear as key=value pairs An attribute must have both a key and a value Attribute keys do not appear in quotation marks Attribute values must appear in quotation marks Remember, single and double quotes are interchangeable A space separates each key=value pair

38. Slide 38 XML Attributes (Example) In the following example, id is the attribute 42

39. Slide 39 Comparing Attributes and Elements The following 2 documents are (roughly) equivalent Bill 12345 Bill

40. Slide 40 Processing XML In Android There are several Android and Java classes with which we can process an XML document Generally speaking we can Read the data sequentially using a SAX parser Read the data into an in-memory XML document, with which we can do some DOM processing We will use a DOM parser My demo continues to work with the weather.

41. Slide 41 Processing XML All XML nodes have a type http://www.w3schools.com/dom/dom_nodetype.asp

42. Slide 42 Processing XML Create a DocumentBuilder via the DocumentBuilderFactory Call the parse method on an input stream to read and parse the document Using the Document object, navigate and work with the in-memory XML document

43. Slide 43 Classes We Need DocumentBuilderFactory DocumentBuilder Document NodeList Node InputSource StringReader

44. Slide 44 The DocumentBuilderFactory Class It lets applications get a parser that produced XML object trees from XML documents This is pretty much the same DOM with which you are familiar (JavaScript) As the name implies, we use a factory class and method to create the

45. Slide 45