Some concepts to understand the things that relate to basics of development on the Android Platform. The presentation explains the concept of formation of virtual machine for each android app. It also explains the main components like Activities, Services, Content Provider and Broadcast Receiver. The purpose of Intent is also explained. One can also find a brief on things that one can write in the Manifest file. The types of resources have also been explained. Finally one learns to know about the android metrics.
4. Basic Fundas
• Programs are mainly written in Java. Can
be written in other languages, but need to
create DVM compatible code.
• Entire Application Code, Data and
Resources are compiled and created into
one package that comes with an .apk
suffix.
• The .apk file is the file that is used to
install applications onto the target system.
5. Application Working Concept
5
Linux
VM1
VM2
VM3
VM4
App-1
App-2
App-3
App-4
App-4
UserID - A
UserID - B
UserID - C
UserID - D
We can arrange for
two apps to share
same VM and same
User ID to share data
Most apps will run in their own
VM and a self generated
UserID (unknown to app)
Apps can make specific requests
to get permission to access
device data like contacts, SMS,
SD card, Camera, Bluetooth.
This permission is specifically
granted at installation time.
6. Application Working
• Each process is started only
when required and shut-off when
not in need, to recover memory
for other application.
• Each applications runs in its own
Sandbox.
8. Power Needs Security
• Each process can use only the
components needed.
• It can not crossover to other memory area
and read/write anything where other
application is doing something.
• This makes it highly secure and free of
memory leaks.
10. Secure Things also need Sharing
• When sharing between applications is
required they share the same Linux user
id.
• Same user Id processes can also arrange
to run in same process and share same
virtual machine.
• Application requests permission to access,
contacts, SD card, SMS etc.
• Permissions are granted by the end user
the time of application installation.
13. Activities
• A single screen with a user interface.
• Activity can be divided into multiple screen areas
called fragments.
• For an Email application
– View Email List Activity
– Compose Email Activity
– View Settings Activity
• Each activity is independent and can be started
by other applications/activities.
• Activities are implemented as a subclass of
Activity.
15. Activitiy-Fragments
• Conceptually fragments allow to define screen area that could be
used as a reusable components by multiple activities.
• A fragment is a sub-activity which has its own lifecycle of creation,
use and destruction, but is paused or destroyed along with its parent
activity.
17. Services
• Some thing that runs in background and
doesn't have a user interface.
• Ex. Playing music in background.
• Ex. Watching whether a new email is
coming.
• It is implemented as a subclass of Service.
• Services are also independent and can be
started by different applications.
18. Content Provider
• It manages a shared set of data.
• In a file system, SQLite, SDCard,
• Through this data query, data update is
possible.
• Permissions need to be set to use any
content.
• Implemented as subclass of
ContentProvider.
19. Broadcast Receiver
• Responds to system wide announcements
• For e.g.
– Battery low
– Screen turned off
– Picture captured
• Application can also initiate broadcast
– Some data has been downloaded.
• Implemented as subclass of
BroadcastReciever.
20. Components Activation
• Components like Activities, services,
broadcast are activated by using Intents.
• Intents are asynchronous in nature.
• The purpose of Intents is to bind
application components together at
runtime.
• They act as messengers between them.
• Created with an Intent object.
• The component ContentProvider is
activated by a request from
23. Manifest Purpose
• It is to tell the system about existence of
various components.
• To tell about user permissions.
• Declaration of API version requirement
• Hardware/Software features required by
the application.
• Libraries the application needs to link.
• Saved as AndroidManifest.xml
25. Manifest Nodes - 1
• uses-permission
requests a permission from user, that must be
granted to operate it correctly.
• permission
permission to use a local resource or activity, as
well as to allow
• permission-tree
declares a base name for a tree of permissions.
•
26. Manifest Nodes - 2
• permission-group
allows to group logically related permissions.
• instrumentation
required to handle instrument class
• uses-sdk
allows to set minimum, maximum and target SDK
version required to run the app.
27. Manifest Nodes - 3
• uses-configuration
allows to set configuration of uses like allowing
keyboard, keyboard type, touch screen uses etc.
• uses-features
allow to set feature uses like for camera,
bluetooth etc.
• supports-screens
allows to set things related to screen sizes and
densities.
28. Manifest Nodes - 4
• compatible-screens
allows to set compatibility of application with
different screens.
• supports-gl-texture
allow to set the type of texture compression used
for storing images.
29. Manifest Nodes - 5
• application
this special node related to application
configuration, further supports sub-nodes such
as:
– activity
– activity-alias
– service
– receiver
– provider
– uses-library
31. Items separate from Source codes
• Defined Strings and other variables.
• Images, Icons etc.
• Layout of activities.
• Audio/Video files.
• Menus, Styles, Colours etc.
32. Understanding Resources - 1
• Resources are carried as integral part of
android apps (apk files).
• Resources are static content which are
fixed for typical apk file.
• One can however dynamically select the
which resource portion to use for a given
action..
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33. Understanding Resources - 2
• The purpose of having external resources
at development time is the maintainability
of application code.
• Resources are usually kept in /res/ folder
of the typical android project.
• Resource can contain the media files or
XML based configuration files
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34. Understanding Resources – 3
• Typically available Resources are
– Animations resources (in res/anim or res/drawables)
– Color State Lists (in res/color), used for control states
likes, pressed, focused etc.
– Image resources (in res/drawables)
– Layouts (in res/layout)
– Menu (in res/menu)
– Values (in res/values/strings.xml,
res/values/dimens.xml, res/values/styles.xml,
res/values/colors.xml)
– Raw Audio/Video files (in res/raw folder)
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35. Understanding Resources – 4
• Preferred Bitmap Graphics used for Android is png
format. Jpg is acceptable. Gif is supported but
discouraged.
• Many drawable folders for bitmap graphics are made
available on the basis of android screen pixel density.
– ldpi (Low density – 120dpi)
– mdpi (Medium density – 160 dpi)
– hdpi (High Density – 240 dpi)
– xhdpi (extra high density – 320 dpi)
– xxhdpi (double extra high density – 480 dpi)
– xxxhdpi (triple extra high density – 640 dpi)
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37. Units used in android apps
• dp or dip – Device independent pixels. Use it for
element sizes (text box, button etc.) and gaps.
Same size feel on different screens. 1px = 1 dp
on mdpi (px = dp * (dpi/160) )
• sp or sip – Scale Independent pixels.
Use it for fonts. Usually equal to dp, but it reacts
to font size configurations.
• ems – Size of width of m of given fonts. Allows
to set relative unit for elements with respect to
font sizes.
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39. 39
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