Training Session 2 - Day 2

Android is built on top of Linux kernel.

Android uses a number of libraries to perform various functionalities.

Just like the Java Virtual Machine in our computers, Android has its
own Dalvik Virtual Machine optimized for itself.

Higher-level services to applications in the form of Java classes:
Application Framework.

Higher-level services to applications in the form of Java classes:
Application Framework.
We will write applications to be installed on the Application layer only.

Android’s defined tags

Introduction to

xml

Used to define some of
the resources
-  Layouts
-  Strings
Used in Android
Manifest
Preferred way for
defining UI elements
-  Separation of
code

LO
AU
YT

Eclipse has a great UI creator
-  Generates all the xml for you
Composed of View objects

Can be speciﬁed for portrait or
landscape
-  Different designs for different
orientation.

VIEWS
A layout/activity is composed of
Views and ViewGroups.
View is something that is visible.
Examples:
- 
- 
- 
- 

TextViews,
Buttons,
TimePicker,
DatePicker

VIEWS
3 ways to declare width and height

a. 
b. 
c. 

ﬁll_parent
wrap_content
match_parent

<Button
android:id = “@+id/button”
android:layout_width = “fill_parent”
android:layout_height = “wrap_content”
android:text = “Button”/>

{

DO NOT FORGET

TO DEFINE US

VIEWS

{

<EditText
android:id = “@+id/number”
android:layout_width = “fill_parent”
android:layout_height = “wrap_content”
android:text = “number”/>

You can change
the type of
inputs as
necessary

VIEWS

<TextView
android:id = “@+id/result”
android:layout_height = “wrap_parent”
android:layout_weight = “fill_content”
android:text = “invisible”/>

3 ways to declare visibility

a. 
b. 
c. 

visible
invisible
gone

FrameLayout

4

One or more View can be
grouped into a ViewGroup

RelativeLayout

3

This is the <body> to your
view.

LinearLayout

2

ViewGroups

1

TableLayout

5

ScrollView, etc.

Each layout has something
unique to it.
Each layout has a purpose!

LinearLayout
Declaring the XML namespace (done
in the 1st ViewGroup)

<LinearLayout
xmlns:android=“http://schemas.android.com/apk/res/
android”
android:layout_width= “match_parent”
android:layout_height= “match_parent”
android:orientation= “vertical”>
… (TextViews, Buttons etc.)
</LinearLayout>
Unique for this ViewGroup
a.  Vertical
b.  Horizontal

RelativeLayout

Does not have any android:orientation.

Affects the layouts inside it

Views are arranged according to references.

RelativeLayout

<RelativeLayout ..>
<Button android:id= “@+id/btn”
android:layout_alignParentTop= "true" … />
<TextView android:layout_below = “@id/btn” … />
<TextView android:layout_toRightOf = “@id/btn” …/>
<TextView android:layout_toLeftOf = “@id/btn” …/>
<TextView android:layout_alignParentBottom =
“true” .../>
</RelativeLayout>
Various other positioning
techniques also there:
alignLeft
alignBaseLine
above, etc.

LinearLayout

vs

RelativeLayout

LETS UNITE!
<LinearLayout … >
<RelativeLayout … >
…
</RelativeLayout>
</LinearLayout>

You can use ViewGroup within ViewGroup

LAYOUTCEPTION!

ENTS

<a href= “target”>page 2</a>

Intent ~ Redirecting !

Intent is used to call into android's drivers,
other applications as well.

Powerful inter/intra application messagepassing framework.

While working with intents we also have to
work with the

Android Manifest

Android Manifest
Presents essential information
about the application to the
Android system
Information the system must have before it
can run any of the application's code.

Manifest
Name of the Java package for the
application.

It describes the components of
the application
the activities, services, broadcast receivers, and
content providers.

Manifest
It declares which permissions the
application must have in order to
access protected parts of the API and
interact with other applications.

It declares the minimum level of the
Android API that the application
requires … and much more.

MODIFICATION IN ANDROID MANIFEST

Declares an activity (an Activity
subclass) that implements part of the
application’s visual user interface.

<activity android:name=".OtherClass">
<intent-filter>
<action android:name="android.intent.action.NAME"/>
<category
android:name="android.intent.category.DEFAULT"/>
</intent-filter>
</activity>
The types of intents that an app can
respond to

Adds an action to an intent ﬁlter

Adds a category name to an intent
ﬁlter

In MainActivity
Intent i = new Intent(MainActivity.this,
OtherClass.class); // Instantiating the intent
class
i.putExtra(“name”, value); // values to be sent
startActivity(i); // Starting the intent

In OtherClass
Intent i = getIntent(); //getting the intent
object
String name = i.getStringExtra(“name”); //
getting value from passed intent

Intents

HAVE YOU EVER WONDERED
WHAT HAPPENS WHEN YOU
PRESS THE BACK BUTTON/
HOME BUTTON ON ANDROID?

Activity
Life
Cycle

onCreate() :
instantiate views, setup
references, implement
listeners.

onPause() :
save data/state in the
application.

onResume() :
can be used to load the
saved state, is always
called when the application
comes into view.

THAT’S ALL FOLKS!
WE’LL SEE YOU TOMORROW

Training Session 2 - Day 2

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Training Session 2 - Day 2