Introduction to Android Programming

Transcription

1 2 Topics of discussion Introduction to Android Programming CS314 Sudipto Ghosh Notes based on contributions from Laura Adams as well as various tutorials on the internet. Adapted by Jim Bieman Web services (just for background) Android applications (needed in P4) Useful references: Vogel s tutorial on Android Development Android developer site: 3 Models and views 4 Model view controller pattern - Pie - O X - Bar - O X a b c a b c - Table - O X a = 50% b = 30% c = 20% a b c x y z MVC components: Model 6 MVC Components: View The processing component which includes the core functionality of the system. This functionality is independent of the output representation or the input behavior. The model interacts with View and Control objects by registering them, and then notifying them when the Model's state changes. The View includes the components that display information to the user. This is the output component. Multiple views are allowed. View objects register with the Model; they retrieve data from the Model when they are notified of an update. 1

2 7 MVC Components: Controller 8 Web application framework This is the input component. There may be a controller for each view. The controller receives input, for example, it interprets mouse movement, buttons, and/or keyboard input. Inputs are received as events, which are translated by the controller into requests for service. The service requests are sent to either the Model or View. The user interacts solely via controllers. 9 Server side 10 Client side Data storage Database File system Memory Server Controller code in PHP, Java,.Net Server framework runs on top of operating system Examples: LAMP Linux, Apache, MySQL, PHP Reads in data from view Renders view in a variety of ways Pushes user data to controller A variety of clients can be supported 11 Client Server Architecture 12 Web service program 2

3 13 Web services 14 Extensible Markup Language (XML) Clients communicate with server over the internet Use Internet protocols to transfer information Example: http Client gets data from a specialized webpage Client can submit data using POST or GET Data is represented as XML (can use JSON as well) Human and machine readable data format Written in plain text Standard practice for web services Parsers exist Components: Tags: <item> ElementsL <item>item 1</item> Content: Item 1 Attributed: <item id= 1 > Elements can be nested 15 XML Example 16 Eclipse demo <menu> Write server code to generate XML files <item id= 1 > Run a web server <pizza name= Pepperoni Pizza > Extend code to take user input through GET <topping>pepperoni</topping> <topping>cheese</topping> </pizza> </item> </menu> 17 Steps for Server 18 Steps for Server [2]: Use controller Create a Java project called Server Include networking capabilities by adding http jar to the buld path Create a simple server called Server Create another class that represents the Controller Call it MenuController Imports a class from the jar file HttpHandler Import com.sun.net.httpserver.httphandler Needs to implement handle() method Print something in the handle method (such as the word Request ) Implement the main method in server Create new HttpServer object with a new socket address and a port 8000 Throws exceptionimport the com. Package and java.net package. Throw exception Instantiate the controller MenuController Specify the URL using server.createcontext( /menu, menu) URL: localhost:8000/menu Start the server: server.start() Run as Java application Open browser and type localhost:8000/menu 3

4 19 Steps for Server [3] 20 Steps for Server [4]: Using model Can t run another server instance at the same time on the same port Handle method isn t very useful Make it do something Capture the information coming in to do something useful and return info Get the URI of the request URI uri = exchange.getrequesturi(); Print it Write a new method to get the XML to return. Call that method. Send the response. Send code 200 in the request to denote everything s good., and the length of the message. Output the data using the OutputStrem class. Close the stream Write the container class for the Model called MenuItem with type, description Generate getters and setters In MenuController class, Create an arraylist of menuitems. Add constructor to initialize arraylist Create some menu items. Add to items Change getxml method to actually go through the items and create an xml version Run the server and reload URL on browser 21 Steps for Server [5]: Using another 22 Steps for Server [6]: Processing the get controller to take user data call Create an Order Controller class Handle method prints order received Create an Order model class Create getters and setters In Main method Create a new Order Controller instance Create context for order Run server and load localhost:8000/order in browser We will use get (it s easier, but you can use post) Copy code from handle in MenuController to OrderController Change response to order submitted Run Server and browser Add?name=Ghosh to URL, type=pizza Run Server and browser Write a method to parse the request called parserequest() 23 Android 24 Android Architecture We will use Android for our client Install Android from this link: Option 1: install Android Studio which is an Eclipse-like environment that supports Java. Option 2: install the combined eclipse/android SDK package, but you can install just the SDK to an existing IDE Launch SDK manager and choose what to download Download everything that is blue under Tools Download Android 5.0 Launch Device Manager and clone a device for Android 5.0 Quite different from desktop applications Focus on Activities Activity: Single focused thing a user can do An app may have more than one activity Activities are stored on the Activity Stack Only visible activity is executed, all others are paused 4

5 25 Activity lifecycle 26 Creating an application File New Other Android Android Application Project Creates a single default Activity with autogenerate methods Android manifest contusing application permissions Add Internet permission if you need to communicate with server R.java file is generated and contains references to resources Res/layout/activity_main.xml is the layout for the activity Name the text view 27 Android demo (Later) 28 Create MainActivity Create a basic application and run on emulator Change the value of layout objects programmatically Make web call using AsyncTask Send data to the server over GET Look at and understand Java file MainActivity XML file AndroidManifest.xml res/values/strings.xml Compare Editing the XML files directly Using the eclipse graphical editor to place GUI elements or set values Start with Hello World and run the app Add new Button, which needs an onclick method name in the android manfest Define buttonclick method in the MainActivity.java file Run the app Explore console output, logcat output 29 Create a new activity that results from 30 Using intent passed to a new activity button click File New Android Activity (blank) Give a name for the activity Give a project where it should go Use Intent to pass information from one activity to the next You can put extra data inside the intent to provide it to the next activity Data is in the form of name, value pair Start the new activity passing the intent Run the app Now to grab the intent in the new activity. Inside the oncreate method, use the getintent method Pull the message out from the Intent. Modify the activity_web_service.xml file to include the id of the TextView you want to modify Create a textview in the oncreate method by using that ID (involes the R.java class) Set the message of the textview Run the app 5

6 31 For apps involving web servers: Write a web call class to get data from the server and update the textview Regular Java class WebCall class extends AsyncTask Implement the method called doinbackground Create the result Provide the URL Create an HttpClient to make the connection Create a new HttpGet object with the URL Create a response from the httpget Get the Entity from the Response Get the input stream form the entity Convert the input stream to a string Make sure you call it in the WebServiceActivity class and update the text in the textview Add internet to the permissions 6