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

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

6. AndroidThemes (continued) • Coding a Theme in the Android Manifest File • Insert this code into the AndroidManifest.xml file android:theme="@android:style/Theme.Black.NoTitleBar“ 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, email, 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