Programming Android UI basics

J. SerratSoftware DesignDecember 2015

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

Preliminaries: why Android

● Many students own an Android phone

● Known and free development environment (Android Studio or Eclipse + ADK plugin)

● Well documented

● Good chance to learn UI design

● Take 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 with 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. TimeTracker architecture

ReferencesPublished since 2010 (O'Reilly, Apress, Wrox, Manning)

and many more ...

References

Beginning Android 4 application development.Wei-Meng Lee. Wiley, 2012. Electronic version at UAB library.

Head first Android development. Dawn Griffiths, David Griffiths. O'Reilly, 2015.

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

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

Development framework

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

Development framework1.6

2.2

4.0

Building blocks

Main logical components of Android applications :

● Activity : UI component typically corresponding to one 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.

ActivityActivity

ApplicationActivityActivity

Application

ActivityActivity

Content ProviderContent Provider

ServiceService

Application

Data file

Data file

SQLite XML file

XML file

Remote Store

Content ResolverContent Resolver Content ResolverContent Resolver

Content ResolverContent 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 occurred 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

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 displayedin the screen

values/strings.xml

other viewsxml 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”). The call setContentView(R.layout.main)“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/editTextLongitud" android:inputType="number" > <requestFocus /> </EditText>

<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 seconds, 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 CycleStates 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 backgroundNot 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() + onCreate(). Ctrl-F11 on virtual device.

Homework recap

● Get some recommended book AND read developer.android.com/training main topics

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

● Import our Android TT project into Android Studio, replace our “nucli.jar” for your package “nucli”, edit code to integrate it and make it work

● Read comments, identify activities, service...

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

http://developer.android.com/guide/topics/ui/controls.html

http://developer.android.com/guide/topics/ui/declaring-layout.html

Views, Layouts

Views, Layouts

Common controls : TextView, EditText (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" >

<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/editTextLongitud" android:inputType="number" > <requestFocus /> </EditText>

<TextView android:id="@+id/textViewLabelUnitatsLongitud" android:text="mm" /> </TableRow> : : </TableLayout> <Button android:id="@+id/butocalcul" android:text="Calcula" />

</LinearLayout>

ToDoList 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 Enter to add as a new item to the ToDo list.

Views, Layouts

main.xml

Views, Layouts

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

Views, LayoutsJava anonymous class

Override onKey of class onKeyListener

Which listeners has an EditText ?

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 in the action bar.

Menus

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+

Action bar (now App bar)

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 overflow

spinnerapp. icon

Action bar

Action bars can be split

Display actions and, if necessary, the action overflow

main action bar

top bar

bottom bar

If the user can navigate, contains the up caret, at a minimum

To quickly switch between the views, use tabs or a spinner in the top/main action bar

Action bar

spinner

action overflow

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: Typically 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.

To show the dialog, call showDialog(int)

To change dialog properties each time the dialog is opened, define onPrepareDialog(int)

1st call showDialog(id) onCreateDialog(id)

onPrepareDialog(id)

onPrepareDialog(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.

To 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 on the sharedPreferences object

Preferences

Add pairs “string,value” to the SharedPreferences object

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

origin 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 within 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' means components 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_LIFEString namedouble longitudedouble latitude

Broadcast Receivers

Broadcast intent type

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 intent type

Broadcast Receivers

Alternatively, register the receiver when MyActivity is visible and unregister when not.

Typically 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 TimerTask or Timer, which are not usable in Android. See code comments and references there.

Harder to destroy by Android OS than activities

TimeTracker architectureShow a part of the tree, the childs of some node

.

P TP P T

P TP I I I

root

different fields

TimeTracker architecture

DONAM_FILLSPUJA_NIVELL

BAIXA_NIVELLDONAM_FILLSENGEGA_CRONOMETREPARA_CRONOMETREPUJA_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 objects.

This avoids serializing the whole or a subtree of activities and intervals, slow if the tree is large!(need to do it every 1, 2 secs.)

Creates a random synthetic but data-consistent large tree (durations and dates)