Programming Android applications: an incomplete introduction J. - - PowerPoint PPT Presentation

Programming Android applications: an incomplete introduction

• J. Serrat

Software Design December 2013

Preliminaries : Goals

• Introduce basic programming Android concepts
• Examine code for some simple examples
• Limited to those relevant for the project at hand
• Provide references to best materials for self

study, read them before programming , trial and error takes longer

• Understand provided project implementation
• Homework for a quick start

Preliminaries: why Android

• Many students own an Android phone
• Known and free development environment

(Android SDK + Eclipse + ADK plugin)

• Well documented
• Good chance to learn UI design
• T

ake away course project in your pocket, funny to see and show your software running in a phone

• Starting point to learn more on mobile

development

Preliminaries: why Android

• Drawbacks: learning curve, lots of details
• Many things left out: fragments, programming

action bars, themes...

• How to learn: try to solve small problems in

separate projects, like

• create an action bar wit actions and overflow

action

• customize a ListView to show name and time
• make a contextual action bar

Contents

• 1. References
• 2. Development framework
• 3. Building blocks
• 4. Structure of an Android project
• 5. Activity life cycle
• 6. Views, Layouts

Contents

• 7. Menus
• 8. Action bar
• 9. Intents, Broadcast receivers, Adapters
• 10. Dialogs, Preferences
• 11. Services
• 12. TimeT

racker architecture

References

Published since 2010 (O'Reilly, Apress, Wrox, Manning) and many more ...

References

Professional Android 4 application

• development. Reto Meier. Wiley, 2012.

Complete, comprehensive, basic and advanced

• topics. I used the Android 2 version to learn.

Source code at eu.wiley.com Hello, Android. 3rd Edition. Ed Burnette. The pragmatic programmers, 2010. Simpler, only basic topics. Sudoku application. Source code at http://pragprog.com/book/eband3/hello-android Android UI fundamentals: develop and

• design. Jason Ostrander. Peachpit, 2012.

Focused on UI only. Example application: a time tracker (1 level). Source code at www.peachpit.com/androiduifundamentals

References

http://cataleg.uab.cat/search*cat/X?SEARCH=%28android%29&SORT=D

December 2013

References

http://developer.android.com/training/index.html

References

In Eclipse, you can install many (legacy) application examples : File → New → Other → Android → Sample project ...

References

Load examples as Eclipse projects: File → New Android project → create from existing sample → Api demos Run and see source code for the API demos.

Virtual device emulator

References

For example, in emulator: Api Demos → Views → Controls → Light theme and in Eclipse:

res/layout/controls_1.xml apis.views/controls1.java

Development framework

http://developer.android.com/resources/dashboard/platform-versions.html

Development framework

1.6 2.2 4.0

Building blocks

Main logical components of Android applications :

• Activity : UI component typically corresponding to
• ne screen. They contain views = UI controls like

buttons, editable text boxes... May react to user input and events (intents) An application typically consists of several screens, each screen is implemented by one activity. Moving to the next screen means starting a new

• activity. An activity may return a result to the

previous activity.

Building blocks

• Service : application part that runs in background

without the user’s direct interaction, similar to a Unix daemon. For example, a music player.

• Content provider : generic interface to manage

(access, change) and share (like “contacts”) application data. Can be stored as SQLite databases.

Activity Application Activity Application Activity Content Provider Service Application Data file SQLite XML file Remote Store Content Resolver Content Resolver Content Resolver

Building blocks

• Intent : “messages” sent by an activity or service

in order to

 launch an activity = show a new screen  broadcast (announce) that a certain event has

• ccurred so that it can be handled

Fundamental to decouple cooperating application components.

• Post 3.0 APIs include some more components:

fragments, tasks...

Building blocks

Structure of an Android project: create and run a “Hello world” application, File → New → Android application project → ...

Do not close the emulator! It takes a lot to start. Each time you build the project, the new version is uploaded and execution starts automatically.

Automatically generated code HelloWordActivity.java

“Inflates” the UI from the main.xml file specifying it Autogenerated class R HelloWordActivity.java

Place to define UI constant strings, values, arrays of integers and strings, colors, size of things (dimensions)... Can use the Resources assistant to edit. values/strings.xml

Message displayed in the screen values/strings.xml

• ther views

xml view AndroidManifest.xml

• includes xml nodes for each of the application

components : Activities, Services, Content Providers and Broadcast Receivers

• using intent filters to specify how they interact

with each other:

 which activities can launch another activity or

service

 which broadcast intents an activity listens to,

in order to handle them with a receiver ...

• offers attributes to specify application metadata

(like its icon or theme) AndroidManifest.xml

This activity may be the application entry point. Won't start on devices supporting an older API AndroidManifest.xml

The interface design is represented in XML, decoupling design from code (opposite to “programmatic UI”). A call “inflates” the UI. Layout is a special view that contains other views in specific spatial arrangements. LinearLayout arranges its children in a single column or row. TextView is a non-editable text label.

XML view of the UI design

layout/main.xml

string id defined in string.xml layout/main.xml

<LinearLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <TextView android:id="@+id/textViewTitol" android:text="TubeQuoter V0.10" /> <TableLayout android:id="@+id/tableLayout1" android:layout_marginLeft="20dp" > <TableRow android:id="@+id/tableRow1"> <TextView android:id="@+id/textViewLabelLongitud" android:text="Longitud" /> <EditText android:id="@+id/editT extLongitud" android:inputT ype="number" > <requestFocus /> </EditT ext> <TextView android:id="@+id/textViewLabelUnitatsLongitud" android:text="mm" /> </TableRow> : : </TableLayout> <Button android:id="@+id/butocalcul" android:text="Calcula" /> </LinearLayout>

layout/main.xml

Graphical view of the UI design, better to design. Select item and edit properties.

layout/main.xml

Activity Life Cycle

• Many Android devices have limited memory,

CPU power, and other resources.

• The OS assures the most important processes

get the resources they need.

• In addition, the OS takes

responsiveness very seriously: if the application does not answer user input (key press...) in < 5 secons, the ANR dialog appears.

Activity Life Cycle

• Each application runs in its own

process, which has a main thread, within which activities, services... run

• The OS ranks processes and

kills those with lowest priority, if some application needs unavailable resources.

• If a process is killed “in the middle”, somehow

data can not be lost.

Activity Life Cycle

Android in practice. Collins, Galpin, Käpler. Manning, 2012.

Activity Life Cycle

States of an activity and methods invoked when changing state

Hello Android. Ed Burnette. The Pragmatic Programmer, 2010

Activity is active = visible in foreground interacting with user Activity is visible in background Not visible. Will remain in memory. Need to save data, such as a database record being edited.

States of an activity and methods invoked when changing state. Changing orientation landscape ←→ portrait calls onDestroy() +

• nCreate(). Ctrl-F11
• n virtual device.

Homework Recap

• Get some recommended book AND read

developer.android.com/training main topics

• Load API demos in Eclipse : File → New → Other

Android → Android project from existing code + select <SDK folder>/android-18/samples/legacy

• Create a Hello world project
• with string and icon resources
• try different nested layouts

Views, Layouts

Control: extension of class View that implements some simple functionality, like a button. ViewGroup : extensions of the View class that can contain multiple child Views (compound controls). Layout managers, such as LinearLayout. Activities represent the screen being displayed to the user. You assign a View or layout to an Activity:

main.xml HelloWordActivity.java

Controls: catalog and appearance depends on API level. Look at

• Eclipse Graphical layout editor : shows controls

depending on the API level of your project.

• Run Api Demos → Views
• developer.android.com/guide/components

Views, Layouts

Views, Layouts

Common controls : T extView, EditT ext (many types), Button, ListView, ExpandableList, Spinner, Checkbox, ProgressBar, SeekBar, RadioGroup, RatingBar, Time and Date Picker …

Views, Layouts

Layouts control the position of child controls on a screen. Common layouts:

• LinearLayout adds each child View in a straight

line, either vertically or horizontally

• RelativeLayout define the positions of child

Views relative to each other or screen boundaries

• TableLayout lay out Views using a grid of rows

and columns Can be nested, creating arbitrarily complex interfaces.

Views, Layouts

1 2 3 4 1 2 3 4

LinearLayout

1 2

Views, Layouts

RelativeLayout

<LinearLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <T extView android:id="@+id/textViewTitol" android:text="T ubeQuoter V0.10" /> <TableLayout android:id="@+id/tableLayout1" android:layout_marginLeft="20dp" > <T ableRow android:id="@+id/tableRow1"> <T extView android:id="@+id/textViewLabelLongitud" android:text="Longitud" /> <EditT ext android:id="@+id/editT extLongitud" android:inputT ype="number" > <requestFocus /> </EditT ext> <T extView android:id="@+id/textViewLabelUnitatsLongitud" android:text="mm" /> </T ableRow> : : </TableLayout> <Button android:id="@+id/butocalcul" android:text="Calcula" /> </LinearLayout>

T

• DoList example : how to react to user input ?

How to bind data to the UI (lists) ?

Views, Layouts

Write to the edit box and then press D-Pad or Enter to add as a new item to the ToDo list. D-Pad

Views, Layouts

Views, Layouts

From now on, changes on ArrayList todoItems are shown in the screen when adapter notifies it.

Views, Layouts

Java anonymous class Override onKey of class onKeyListener Which listeners has an EditT ext ?

Views, Layouts

It is possible to customize the aspect and content of items in a ListView. See Ch. 4 Reto Meier's book and source code at www.wrox.com

Contents

• 7. Menus
• 8. Action bar
• 9. Intents, Broadcast receivers, Adapters
• 10. Dialogs, Preferences
• 11. Services
• 12. TimeTracker architecture

Menus

Present application functionality using little screen space. Each Activity can specify its own menu. Difference between pre and post 3.0 platform (API level 10):

• pre: physical menu button on the device, three

levels of menus: options, expanded, submenu

• post: superseded by the action bar

Menus

phones with physical navigation keys virtual navigation controls

Menus

Three types of menus

• 1. Options menu
• at the bottom of screen
• icons and text
• if more than 6 items, a More item is displayed

that opens an Expanded menu

• On Android 3.0 and higher, items from the
• ptions menu are presented by the action bar

Menus

action bar expanded menu

Menus

• 2. Context menu
• floating menu that appears when the user

performs a long-click on an element

• similar to “right-click” menu
• provides actions that affect the selected

content, normally an item of a ListView

Menus

• 2. Context menu
• from Android 3.0 on, better use a contextual

action bar to present actions the user can perform on the currently selected item

context menu contextual action bar: actions depend on selected item(s) pre 3.0 3.0+

Menus

• 3. Popup or submenu
• modal menu anchored to a View, appears

below or above it

• good to provide an overflow of actions that

relate to specific content or to provide options for a second part of a command/menu item

• no icons

action overflow : less often used actions submenu title

Menus

• 3. Popup or submenu
• but can't be nested: a submenu item can not

expand another submenu

• On Android 3.0+ : actions should not directly

affect the corresponding content—that's what contextual actions are for

Context menu and submenu for an item

Menus

Programming (1) Recommended: define menu items and properties as a menu resource in XML , not in the code

• easier to visualize the menu structure
• allows to create alternative configurations for

different platform versions, screen sizes...

• compact code: menu is inflated by a single

call

• can use Eclipse's resource editor

Menus

Menus

to reference the menu options in the code : what's been selected? string resource name that will appear in the UI, better use array of strings in xml

Menus

Programming (2) Override Activity method to inflate the xml menu

res/menu/game_menu.xml

Menus

Programming (3) Program event handling : when the user selects an item from the options menu (also action items in the action bar), the system calls the activity's method

selected item item ids

Menus

Spinners offer similar functionality: multiple choice selection from exclusive options on a dropdown menu. Menu items can contain radiobuttons but also checkboxes and form groups

Not a menu control!

Action bar

Replaces the options menu in Android 3.0+ with buttons ('action items') One of the most important design elements of an Android app. :

• dedicated piece of screen
• visible throughout the app.

running

• makes our app. consistent with

the core Android apps.

Action bar

Examples

Action bar

Purposes :

• make important actions prominent and

accessible [3]

• support consistent navigation and view

switching [2] (with spinner or tabs)

• reduce clutter by providing an action overflow

for rarely used actions [4]

• show app identity [1]

action buttons action

• verflow

spinner app. icon

Action bar

Action bars can be split

Display actions and, if necessary, the action

• verflow

main action bar top bar bottom bar If the user can navigate, contains the up caret, at a minimum T

• quickly switch between

the views, use tabs or a spinner in the top/main action bar

Action bar

spinner action

• verflow

Dialogs

Small windows displayed over the screen.

• modal: block all user input and

must be dismissed before the user can continue.

• partially obscures the Activity that

launched it. Purposes : answer questions Yes/No, Ok/Cancel... make selections read warning or error messages show bar progress

Dialog share a common structure:

• Optional title region: Introduces

content

• Content area: text, UI elements,

text fields, checkboxes, etc...

• Action Buttons: T

ypically OK/Cancel, indicating the preferred option.

Dialogs

Special types of Dialogs:

• Alerts: Inform user from a

situation that requires confirmation.

• Pop-ups: Lightweight

dialogs with a single selection from the user.

• Toasts: Small pop-up that

feedbacks about

• something. Disappear

automatically.

Dialogs

Dialogs

Programming (1) Dialogs should normally be created(instantiated) within the Activity's onCreateDialog(int). This is called only the first time the dialog is showed. T

• show the dialog, call showDialog(int)

T

• change dialog properties each time the dialog

is opened, define onPrepareDialog(int)

1st call showDialog(id)

• nCreateDialog(id)
• nPrepareDialog(id)
• nPrepareDialog(id)

2nd call showDialog(id)

Programming (2) The best way to define onCreateDialog(int) is with a switch statement that checks the id of the dialog being created. The method must return the dialog created.

Dialogs

Programming (3) When it's time to show one of the dialogs, call showDialog with the desired ID. T

• close a dialog, you can dismiss it by calling

dismiss() from the Dialog object. If necessary, you can also call dismissDialog(int) from the Activity.

Dialogs

Preferences

Android provides classes to manage application preferences and implement the preferences UI.

• ensures consistency, with

specific UI elements (e.g ListPreference)

• all preferences within each

application is maintained in the same manner.

Preferences

The SharedPreferences class:

• provides a general framework to save and

retrieve key-value pairs.

• there is a single instance of this class.
• its data will persist across user sessions (even if

the app is killed)

Preferences

Steps to implement the Preferences:

• 1. Add string resources needed for preferences.

Preferences

• 2. Create the preferences UI layout (using

standard Preference UI elements).

We can reference the string resources

Preferences

• 3. Create the Preferences Activity, and inflate the

layout overriding the onCreate method.

• 4. Add static string values to identify each of the

preferences by a unique key.

Preferences

• 5. Implement the OK/Cancel listeners and a

method to save preferences.

This method commits changes

• n the sharedPreferences object

Preferences

Add pairs “string,value” to the SharedPreferences

• bject

Commit changes. If the preferences file MYPREFS does not exist, it will be created

• 5. Implement the OK/Cancel listeners and a

method to save preferences.

Preferences

• 6. Apply the preferences when the activity starts.

Preferences file

• name. If it does not

exist will be created when committing changes Unique preference key (string) Default value if it is not defined

Intents

Intents is a fundamental concept in Android development : “the glue that binds applications' components”. Message-passing mechanism to

• explicitly or implicitly start an Activity or a

Service

• broadcast that an event has occurred,

application or system-wide to handle user action or process a piece of data

Intents

Intents

• rigin

context activity to start Intents can return a result: startActivityForResult()

Intents

Need to declare all activities in AndroidManifest.xml

Broadcast Receivers

Intents can also be used to broadcast messages to anonymous components with one same application. The sender can associate data to those intents. A broadcast receiver (maybe within other app. component):

• listens for selected types of broadcast intents
• responds to them = processes associated data

'Anonymous' implies components are loosely coupled, do not need to know each other.

Broadcast Receivers

On button click a broadcast intent of type “NEW_LIFE” is sent, along with three data fields. A broadcast receiver object has subscribed to this type of messages in the AndroidManifest.xml. The receiver does not belong to an Activity or Service in this case. Response is printing a message.

NEW_LIFE String name double longitude double latitude

Broadcast Receivers

Broadcast Receivers

data field names Broadcast intent type

Broadcast Receivers

The broadcast receiver will always be active (listening), even when MyActivity has been killed or not started

Broadcast Receivers

Register the receiver when MyActivity is visible and unregister when not. T ypically when the receiver updates am UI element.

TimeTracker architecture

LlistaActivitatsActivity.java LlistaIntervalsActivity.java ListView controls

TimeTracker architecture

Contains the actual activities and intervals tree Analogous to TimerT ask or Timer, which are not usable in Android. See code comments and references there. Harder to destroy by Android OS than activities

TimeTracker architecture

Show a part of the tree, the childs of some node . P T P P T P T P I I I

root

different fields

TimeTracker architecture

DONAM_FILLS PUJA_NIVELL BAIXA_NIVELL DONAM_FILLS ENGEGA_CRONOMETRE PARA_CRONOMETRE PUJA_NIVELL

TimeTracker architecture

TE_FILLS + array of project and task data : dates and duration TE_FILLS + array of interval data : name, dates and duration

TimeTracker architecture

Intent data to activities is a serialized array list of these

• bjects.

This avoids serializing the whole or a subtree of activities and intervals, slow if the tree is large! (need to do it every 2 secs.) Creates a random synthetic but data-consistent large tree (durations and dates)