1. Chapter 3: Engage! Android User Input, Variables, and Operations

2. Objectives In this chapter, you learn to: Use an Android theme
Add a theme to the Android Manifest file
Develop the user interface using Text Fields
State the role of different Text Fields
Display a hint using the Hint property
Develop the user interface using a Spinner control
Add text to the String table
Android Boot Camp for Developers using Java

3. Objectives (continued)
Add a prompt to the Spinner control
Declare variables to hold data
Code the GetText() method
Understand arithmetic operations
Convert numeric data
Format numeric data
Code the SetText() method
Run the completed app in the emulator
Android Boot Camp for Developers using Java

4. Android Themes
Engaging the user by requesting input customizes the user experience each time the application is executed
A theme is a style applied to an Activity or an entire application
The default theme is a title bar (often gray) with a black background
Android Boot Camp for Developers using Java

5. Android Themes (continued)
Figure 3-3 Default Theme
Figure 3-4 Holographic Theme
Previewing a Theme
Check the main.xml file in the emulator to see what your screen looks like
Android Boot Camp for Developers using Java

6. Android Themes (continued)
Coding a Theme in the Android Manifest File
Insert this code into the AndroidManifest.xml file
Figure 3-10 Adding the theme to the Android Manifest File
Android Boot Camp for Developers using Java

7. Simplifying User Input
The onscreen keyboard is called a softkeyboard
Input can be in the form of tapping or gestures (using two fingers to pan, rotate, or zoom)
Primary design challenge is to simplify user experiences
Use legible fonts, simplify input, and optimize each device’s capabilities to maximize user experience
Figure 3-13 Onscreen keyboard
Android Boot Camp for Developers using Java

8. Simplifying User Input (continued)
Android Text Fields
Text Fields are the most common type of mobile input
Can be free-form plain text
Numbers
A person’s name, password, , phone number
A date
Multiline text
Android Boot Camp for Developers using Java

9. Simplifying User Input (continued)
Figure 3-12 Types of Text Fields controls
Android Boot Camp for Developers using Java

10. Simplifying User Input (continued)
Adding a Text Field
Use the Id property in the Properties pane to enter a name that begins with the prefix txt
Use descriptive names like txtTickets instead of txtText1
Figure 3-14 TextView control added and formatted
Android Boot Camp for Developers using Java

11. Simplifying User Input (continued)
Setting the Hint Property for the Text Field
A hint is a short description of a field visible as light-colored text (called a watermark)
Figure 3-17 Hint added to text Field control
Android Boot Camp for Developers using Java

12. Simplifying User Input (continued)
Coding the EditText Class for the Text Field
A variable is used in programming to contain data that changes during the execution of a program
Final variables can be initialized but cannot be changed
Insert this code to create a variable:
final EditText tickets=(EditText) findViewById(R.id.txtTickets);
Android Boot Camp for Developers using Java

13. Simplifying User Input (continued)
Figure 3-18 Coding the EditText class for the Text Field
Android Boot Camp for Developers using Java

14. Simplifying User Input (continued)
Android Spinner Control
A Spinner control is similar to a drop-down list for selecting a single item from a fixed list
The spinner control displays a list of strings called items in a pop-up window
A string is a series of alphanumeric characters that can include spaces
Android Boot Camp for Developers using Java

15. Simplifying User Input (continued)
Using the String Table
A file named strings.xml is part of all Android apps and contains a list of commonly used strings
Android loads the resources from the project’s String table
Android can select text using Localization which allows for changing text based on the user’s preferred language
A prompt is used to display instructions at the top of the spinner control
Android Boot Camp for Developers using Java

16. Simplifying User Input (continued)
Adding a Spinner Control with String Array Entries
A Spinner property named Entries connects the String Array to the Spinner control
Coding the Spinner Control
Figure 3-26 Coding the Spinner Control
Android Boot Camp for Developers using Java

17. Simplifying User Input (continued)
Adding the Button, TextView, and ImageView Controls
Figure 3-27 Adding a Button control
Android Boot Camp for Developers using Java

18. Simplifying User Input (continued)
Figure 3-28 Coding the button
Android Boot Camp for Developers using Java

19. Simplifying User Input (continued)
Figure 3-29 Adding a TextView control to display results
Android Boot Camp for Developers using Java

20. Simplifying User Input (continued)
Figure 3-30 Assigning the TextView control to a variable
Android Boot Camp for Developers using Java

21. Simplifying User Input (continued)
Figure 3-31 Adding a ImageView control
Android Boot Camp for Developers using Java

22. Declaring Variables Primitive Data Types
Table 3-1 Primitive data types in Java
Android Boot Camp for Developers using Java

23. Declaring Variables (continued)
String Data Type
A string can be a character, word, or phrase
Declaring the Variables
Typically declared at the beginning of an Activity
Variables must be declared before you can use them
Android Boot Camp for Developers using Java

24. Declaring Variables (continued)
Figure 3-32 Declaring variables for the Activity
Android Boot Camp for Developers using Java

25. Declaring Variables (continued)
GetText() Method
Read data stored in the EditText control with the GetText() method
Data is read in as a string, by default
A Parse class is used to convert strings into numbers
Table 3-2 Parse type conversions
Android Boot Camp for Developers using Java

26. Working with Mathematical Operations
Arithmetic Operators
Table 3-3 Java arithmetic operators
Android Boot Camp for Developers using Java

27. Working with Mathematical Operations (cont’d)
Formatting Numbers
Currency format requires a dollar sign, a comma (if needed), a decimal point, and two decimal places
Java has a class called DecimalFormat that provides patterns, such as $###,###.## for displaying on the Android screen
Figure 3-34 Calculating and formatting the ticket cost
Android Boot Camp for Developers using Java

28. Displaying Android Output
GetSelectedItem() Method
The GetSelectedItem() method returns the text label of the currently selected Spinner item
SetText () Method
The SetText() method displays text in a TextView control
Android Boot Camp for Developers using Java

29. Displaying Android Output (continued)
Figure 3-35 Completed code
Android Boot Camp for Developers using Java

30. Summary
Assign a theme to an Activity or an entire application to prevent apps from looking too similar
Define a theme in the Android Manifest file for each Activity
Use Text Fields to request input from users
Use a control’s Hint property to provide guidelines to users so they know what to enter
Use the EditText class to extract text users have entered and store that text in a variable
Use GetText() to get data and SetText() to display data
Android Boot Camp for Developers using Java

31. Summary (continued) Strings.xml is part of every Android application
You can edit a string in the strings.xml file to update text anywhere in the application
Use GetSelectedItem() to return the text of the selected Spinner item
To use a variable, you must first declare it
Variables are declared at the beginning of an Activity
Convert variables to the correct data type using the Parse class
Android Boot Camp for Developers using Java