Android development-workshop-v2-1228043706544191-8

copyright © 2008 cod technologies ltd www.codtech.com

mobile dev campandroid development workshop

diego torres [email protected]

amsterdam, november 2008


“I have always wished that my computer would be as easy to use as my telephone.

My wish has come true.

I no longer know how to use my telephone.”

Bjarne Stroustrup


agenda

● introduction to android

● android architecture

● building blocks

● your first android application

● testing and performance

● best practices


introduction to android

● identify unique features of android platform

● compare android against other platforms

● understand android building blocks

after this section you will...


what is android ?● android is the first complete, open

and free mobile platform● developed by Open Handset

Alliance● software stack than includes

– operating system– middleware– key applications– rich set of APIs

Portions of this page are reproduced from work created and shared by Google and used according to terms described in

the Creative Commons 2.5 Attribution License.


is android linux ?

● no native windowing system

● no glibc support● no GNU/Linux utilities

android is based on a linux kernel but it's not GNU/Linux

NO, android is not linux !


so is android java ?

● uses the java language● implements part of the

Java5 SE specification● runs on a dalvik virtual

machine instead of JVM

android is not an implementation of any of the Java variants

NO, android is not java !


android linux kernel

● security● memory management● process management● network stack● driver model● abstraction layer

android is based on a linux 2.6 kernel, prnel, providing

kernel source: source.android.com


linux kernel enhancements

● alarm● ashmem● binder● power management● low memory killer (no swap space available)

● logger

android introduces some linux kernel patches


unique platform characteristics

● open source

● “all applications are equal” model

● dalvik virtual machine

android characteristics not found on other platforms


other characteristics

● application framework enabling reuse of components

● integrated browser based on WebKit OSS engine

● 3D graphics based on the OpenGL ES

● SQLite for structured data storage

● media support for common audio, video, and still images

● camera, GPS, compass, and accelerometer

interesting features as well, but they are more common across other mobile platforms


android architectureco

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android building blocks

● recognize the fundamental building blocks

● use these building blocks to create applications

● understand applications lifecycle


building blocks


Activities

● Activities are stacked like a deck of cards

● only one is visible

● only one is active

● new activities are placed on top


Activities lifecycle

rectangles are callbacks wherewe can implement operationsperformed on state changes


Activities states● active

– at the top of the stack

● paused– lost focus but still visible– can be killed by LMK

● stopped– not at the top of th stack

● dropped– killed to reclaim its memory


Views

● Views are basic building blocks

● know how to draw themselves

● respond to events

● organized as trees to build up GUIs

● described in XML in layout resources


pattern: load layout

android compiles the XML layout code that is later loaded in code usually by

public void onCreate(Bundle savedInstanceState) { ... setContentView(R.layout.filename); ...}


Views and Viewgroups● Views and

Viewgroups trees build up complex GUIs

● android framework is responsible for– measuring– laying out– drawing


pattern: ids

using a unique id in a XML View definition permits locating it later in Java code

private View name;

public void onCreate(Bundle savedInstanceState) { ... name = (View) findViewById(R.id.name); ...}


Intents● Intents are used to move from Activity to Activity● describes what the application wants● provides late runtime binding

primary attributes

attribute description

action

data

the general action to be performed, such as VIEW, EDIT, MAIN, etc.

the data to operate on, such as a person record in the contacts database, as URI


intents playground

http://codtech.com/android/IntentPlayground.apk


Services

● services run in the background

● don't interact with the user

● run on the main threadof the process

● is kept running as long as

– is started

– has connections


Notifications

● notify the user about events

● sent through NotificationManager

● types

– persistent icon

– turning leds

– sound or vibration


ConentProviders

● ContentProviders are objects that can

– retrieve data

– store data

● data is available to all applications

● only way to share data across packages

● usually the backend is SQLite

● they are loosely linked to clients

● data exposed as a unique URI


AndroidManifest.xml● control file that tells

the system what to do and how the toplevel components are related

● it's the “glue” that actually specifies which Intents your Activities receive

● specifies permissions



your first android

● create your own android map project

● design the UI● externalize resources● react to events● run the application


android project


default application● autogenerated

application template● default resources

– icon– layout– strings

● default AndroidManifest.xml

● default run configuration


designing the UIthis simple UI designs contains● the window title

● a spinner (drop down box) containing the desired location over the map

● a map displaying the selected location


create the layout

● remove old layout● add a RelativeLayout● add a View (MapView not

supported by ADT)

● replace View by com.google.android.mapview

● change id to mapview● add a Spinner filling

parent width


run the application

● com.google.android.maps it's an optional library not included by default

● add <uses-library android:name="com.google.android.maps" /> to manifest as application node


Google Maps API key

● checking DDMS logcat we find

● to access Google Maps we need a key● application must be signed with the same key● key can be obtained from Google● MapView should include

java.lang.IllegalArgumentException: You need to specify an API Key for each MapView.

android:apiKey="0GNIO0J9wdmcNm4gCV6S0nlaFE8bHa9WXXXXXX"


MapActivy

● checking DDMS logcat again

● change base class to MapActivity

● fix imports

● add unimplemented methods

java.lang.IllegalArgumentException: MapViews can only be created inside instances of MapActivity.


where is the map ?

● still no map displayed

● check DDMS logcat

● lots of IOExceptions !

● some uses permissions are missing

– ACCESS_COARSE_LOCATION

– INTERNET


finally our map

still some problems ...

● spinner is covered

● has no prompt

● externalize resource

android:layout_alignParentTop="true"

prompt: @string/prompt


pattern: adapters

an Adapter object acts as a bridge between an AdapterView and the underlying data for that view

ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource( this, R.array.array, android.R.layout.layout);

view.setAdapter(adapter);

The Adapter is also responsible for making a View for each item in the data set.


pattern: resources

resources are external files (that is, noncode files) that are used by your code and compiled into your application at build time.

<resources> <string-array name=”array”> <item>item</item> </string-array></resources>

res = getResources().getType(id);

arrays.xml

<?xml version="1.0" encoding="UTF-8"?>

<resources>

<string-array name="location_names"><item>Mediamatic Duintjer</item><item>NH Hotel</item><item>Airport</item>

</string-array>

<string-array name="locations"><item>52.363125,4.892070,18</item><item>37.244832,-115.811434,9</item><item>-34.560047,-58.44924,16</item>

</string-array></resources>


complete the class● create the locations array

● get the views (ids pattern)

● create the adapter

locations = getResources().getStringArray(R.array.locations);

spinner = (Spinner) findViewById(R.id.Spinner01);mapView = (MapView) findViewById(R.id.mapview);

ArrayAdapter<CharSequence> adapter = ArrayAdapter. createFromResource(this, R.array.location_names, android.R.layout.simple_spinner_item);spinner.setAdapter(adapter)


almost there● map is displayed● spinner is displayed● drop down is

displayed● but there's no

selection button ...adapter. setDropDownViewResource( android.R.layout.simple_spinner_dropdown_item);


respond to events● when an item is

selected map should be centered at that location

● invoke goToSelectedLocation(arg2);

spinner. setOnItemSelectedListener( new OnItemSelectedListener() { });


goToSelectedLocation

protected void goToSelectedLocation(int position) {String[] loc = locations[position].split(",");

double lat = Double.parseDouble(loc[0]);double lon = Double.parseDouble(loc[1]);int zoom = Integer.parseInt(loc[2]);

GeoPoint p = new GeoPoint((int)(lat * 1E6), (int)(lon * 1E6));

Log.d(TAG, "Should go to " + p);

mapController.animateTo(p);mapController.setZoom(zoom);

}


more events● turn map clickable

● override onKeyDown

android:clickable="true”

switch (keyCode) {case KeyEvent.KEYCODE_I:

mapController.zoomIn();break;

case KeyEvent.KEYCODE_O:mapController.zoomOut();break;

case KeyEvent.KEYCODE_S:mapView.setSatellite(

!mapView.isSatellite());break;

}


we did it !

● Some things to try

– select a location

– pan

– zoom in

– zoom out

– toggle satellite


“Remember that there is no code faster than no code”

Taligent's Guide to Designing Programs



testing and performance

● understand the best practices to develop for android

● identify the alternatives to test units, services and applications

● performance


best practices

● consider performance, android is not a desktop● avoid creating objects● use native methods● prefer virtual over interface● prefer static over virtual● avoid internal getter/setters● declares constants final● avoid enums


testing

● android sdk 1.0 introduces

– ActivityUnitTestCase to run isolated unit tests

– ServiceTestCase to test services

– ActivityInstrumentationTestCase to run functional tests of activities

● ApiDemos includes some test samples

● monkey, generates pseudorandom of user events


performance

Action Time

1

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5

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1 2

.1 2 5

1 5

1 65

60 0

220 0 0

250 0 0

1 0 0 0 0 0

1 350 0 0

30 0 0 0 0 0

Add a local variable Add a member variable

Call String.length()Call empty static native methodCall empty static method

Call empty virtual method Call empty interface method Call Iterator:next() on a HashMap Call put() on a HashMapInflate 1 View from XML Inflate 1 LinearLayout with 1 TextView Inflate 1 LinearLayout with 6 ViewInflate 1 LinearLayout with 6 TextView

Launch an empty activity

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summary● introduction to android● android building blocks●


“If things seem under control, you're not going fast enough.”

Mario Andretti


thank youandroid development workshop

diego torres [email protected]

Android development-workshop-v2-1228043706544191-8

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