Tip Calculator App Building an Android App with Java ©1992-2013 by Pearson Education, Inc. All...

Tip Calculator AppBuilding an Android App with Java

©1992-2013 by Pearson Education, Inc. All Rights

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Test driving the Tip Calculator App©1992-2013 by Pearson Education, Inc. All Rights

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Technologies Overview

• This chapter uses many Java OO programming capabilities▫ Classes▫ Anonymous inner classes▫ Objects▫ Methods▫ Interfaces ▫ Inheritance

• We’ll create a subclass of Activity class to programmatically define the logic

• Programmatically interact with EditText, TextView and SeekBar

• We’ll use event handing and anonymous inner classes to process GUI’s interactions


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Building the App’s GUI•We’re using TableLayout to arrange GUI components▫6 rows, 4 columns▫Each cell can be empty or hold one component –

which can be a layout to contain other components▫A component can span multiple columns (SeekBar)▫A row’s height is determined by tallest component

Similarly column’s width by widest component or wider ▫By default, components added to a row left to right▫Can specify exact location – rows, columns start at 0 by

default


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Layout©1992-2013 by Pearson Education, Inc. All Rights

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Names of GUI components in this app©1992-2013 by Pearson Education, Inc. All Rights

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TableLayout and Components•Start with basic layout and controls•Customize control’s properties•As you add components▫Set the ID property▫Set the Text property

• Literal string values should be placed in the strings.xml file in the app’s res/values folder, esp. if you intent to localize app for multiple languages▫Author chose not to use string resources for % TextViews

•Build in exact order specified▫If you don’t, you can rearrange in Outline or in

main.xml


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StepsNOTE: Author uses Outline window to add components to proper TableRows of TableLayout. With more complex Layouts, you can use Visual Layout Editor. (Author thinks it’s easier to use Outline.)

1.Create Project2.Delete and Recreate main.xml file3.Configure Visual Layout Editor to use Appropriate Android SDK4.Configure Visual Layout Editor’s Size and Resolution5.Configure TableLayout6.Add TableRows7.Add Components for tableRow0 – tableRow5


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Review Layout

• billEditText and customSeekBar do not span columns yet

• text is light gray and hard to read

• some components are in wrong columns – will self-correct after we fix customSeekBar

• text is all left-aligned


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Customizing Componets

• Change text colors of TextViews• Move 10%-20% to correct columns• Center Text• Span elements properly• Right align TextViews in column 0• Vertically center TextViews in 5th row• Set SeekBar’s properties• Prevent user from manipulating text in EditTexts other than

billEditText• Set Layout weights for various components to fit on screen


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Final XML Markup


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Editing string resources©1992-2013 by Pearson Education, Inc. All Rights

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Adding Functionality to App©1992-2013 by Pearson Education, Inc. All Rights

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Adding Functionality• Open source code• Add comments at top of file• Add import statements• Android apps do not have a main method▫ Have activities, services, content providers and broadcast receivers▫ The TipCalculator app has only one Activity class, which extends

(inherits from) class Activity.• Add instance variables• Override OnCreate and onSaveInstanceStatemethods• Add method updateStandard, update updateCustom• Add anonymous inner class that implements interface

OnSeekBarChangeListener, and TextWatcher and overrided some of their methods


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package and import statements• Class Activity – provides basic lifecycle methods of an app• Class Bundle – represent’s an app’s state info, so app can save its state

when sent to background• Interface Editable – change content and markup of text in GUI• Interface TextWatcher to respond to events when user interacts with

EditText component• Package widget – contains widgets (GUI components) and layouts used in

GUIs


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• Interface OnSeekBarChangeListeners – responds to user moving the SeekBar’s thumb

Activity

Throughout its life an activity can be in several states•Active (running)•Paused (but visible-not focused-could be killed)•Stopped (not visible – likely to be killed)Methods associated with state transitions (pg. 108)


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Keep this method simple, It has to load in 5 seconds!Time consuming initializationsshould be done in a backgroundprocess.

Key/value pairs

Must call superclass methodwhen overriding any Activitymethod

R is a class built by ADT whenyou build GUI (see gen folder)contains nested static classes representing each type of resourceIn your res folder


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Programmer-defined method


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In Eclipse, you can generate a shell of this method by right clicking in the sourceCode, then selecting Source > Override|Implement Methods…Dialog shows you every method that can be overridden or implementedin a class


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Line 81 registered thisas customSeekBar’sevent-handling object

Java requires weoverride every methodof an interface we implement (even if wedon’t use them)


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Wrap-Up

•Created first interactive Android app▫Overviewed, test-drove, followed detailed instructions

to build GUI using ADT’s Plugin’s tools in Eclipse Including Visual Layout Editor, the Outline Window and

the Properties Window▫Edited main.xml file▫Did a detailed code walkthrough of Activity class

•Future chapters only discuss new GUI capabilities as needed


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Learned• TableLayout▫ Each cell can be empty, hold one component – which could itself be a

layout• TableRow▫ Number of columns determined by the row with most components▫ Row’s height determined by tallest component▫ Column’s width by widest component, unless you stretch them

• TextView▫ Is a label

• EditView▫ Receives input from the user, non-focusable Edit Texts to display various values

• SeekBar▫ Allow user to specify custom values on a scale


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Learned many Java OO concepts

•Final static•Classes▫Overriding methods

•Subclasses (extending/inheriting from)•Anonymous inner classes•Objects•Methods• Interfaces•Get references to GUI components that the app

interacts with programmatically


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Next chapter

• Learn about collections• Layout GUI programmatically – allowing you to add

and remove components dynamically in response to user’s interactions


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Tip Calculator App Building an Android App with Java ©1992-2013 by Pearson Education, Inc. All...

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