- Introduction to intents & intent filters. - How intents and intent filters work. Presentation by: Sharafat Ibn Mollah Mosharraf sharafat_8271@yahoo.co.uk http://www.sharafat.co.cc

1. Android Insights - 1
Intents

2. Topics to be Covered
• Basic Components of Android
• Intents & Intent Filters
• Intent Resolution
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3. Basic Components of Android
• Activity
– provides a screen with which users can interact in
order to do something
• Service
– performs long-running operations in the background
and does not provide a user interface
• Content Provider
– manages access to a structured set of data
• Intent
– an abstract description of an operation to be
performed
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4. Motivation Towards Intents
• We want all the activities, services, broadcast
receivers etc. to be loosely-coupled.
• Message Passing is the way to go.
• Intents are those messages which are used to
communicate among the components.
Remember? “An intent is an abstract description
of an operation to be performed.”
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5. Primary Structure of an Intent
• Action
– The general action to be performed
• Data
– The data to operate on, expressed as a URI.
Example of an action-data pair:
ACTION_VIEW content://contacts/people/1
Display information about the person whose identifier
is "1".
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6. How Intents Work
• Given an arbitrary intent we need to know what to do
with it.
• This is handled by the process of Intent
resolution, which maps an Intent to an
Activity, BroadcastReceiver, or Service (or sometimes
two or more activities/receivers) that can handle it.
• The intent resolution mechanism basically revolves
around matching an Intent against all of the <intent-
filter> descriptions in the installed application
packages.
• There is a manifest file in the next slide where activities
are marked with the intents they can operate on.
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7. How Intents Work...
What are those category and data elements in intent filters??
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8. The Other Parts of Intent
• Category
– Gives additional information about the action to execute.
– For example, CATEGORY_LAUNCHER means it should appear in the Launcher as a top-level
application.
• Type
– Specifies an explicit type (a MIME type) of the intent data.
– Normally the type is inferred from the data itself. By setting this attribute, you disable that
evaluation and force an explicit type.
– For example, setting type to image/jpeg means the activity can handle only jpeg files and not
other image files such as png, gif etc.
• Extras
– A Bundle of any additional information.
– Can be used to provide extended information to the component.
– For example, an ACTION_HEADSET_PLUG has a "state" extra indicating whether the headset is
now plugged in or unplugged, as well as a "name" extra for the type of headset.
• Flags
– Flags of various sorts.
– For example, in the case of FLAG_ACTIVITY_NO_ANIMATION, if set in an Intent passed to
Context.startActivity(), this flag will prevent the system from applying an activity transition
animation to go to the next activity state.
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9. Explicit Intents
Hey, the Intent-Resolution mechanism of Android is cool, but
I just need to start a new activity – that’s all. All those fuzz
aren’t worth of merely starting an activity, I guess???
• You’re right.
• There is a last part in an intent – Component.
• An intent can have specified a component (via
setComponent(ComponentName) or
setClass(Context, Class)), which provides the exact class to be
run.
• Often these will not include any other information, simply being a
way for an application to launch various internal activities it has as
the user interacts with the application.
• Intents having components set are called Explicit Intents in contrast
to their counterparts Implicit Intents.
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10. References
• Intent Structure and Intent Resolution
Mechanism:
http://developer.android.com/guide/topics/in
tents/intents-filters.html
• Standard actions, categories, flags and extra
data:
http://developer.android.com/reference/andr
oid/content/Intent.html
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