Download Android Intents and intent filters By Shinping R. Wang

Android Intents and intent filters
By Shinping R. Wang
CSIE Dept. of Da‐yeh University
Reference

The following discussion is excerpted from
Intents and intent filters
http://developer.android.com/guide/topics/intents/intentsfilters.html
1.
Intent
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Three of the core components of an application —
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activities,
services, and
broadcast receivers —
are activated through messages, called intents.
Intent
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Runtime binding/late binding
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An Intent provides a facility for performing late runtime
binding between the code in different applications.
Intent
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Intent
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serves as glue between activities.
is basically a passive data structure holding an abstract
description of an action to be performed.
Intent
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There are separate mechanisms for delivering intents to
each type of component:
Targeting component types
Corresponding methods for delivering an intent object
Activity
Context.startActivity()
Activity.startActivityForResult()
Activity.setResult()
Service
Context.startService()
Context.bindService()
Broadcast receiver
Context.sendBroadcast()
Context.sendOrderedBroadcast()

For example,
To invoke a started service, you call
Context.startService(intent)
With associated intent
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Activity.setResult()
Context.sendStickyBroadcast()
Intent Objects
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In general, an intent object contains following
information:
Types
Description
Component name
the name of the component that should handle the intent
Action
a string naming the action to be performed
Data
the URI and the MIME type of the data to be acted on.
Category
a string about the kind of component that should handle the
intent.
Extras
Key-value pairs for additional information to the target
component.
Flags
flags of various control purposes.
Intent Objects
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Component name,
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The name of the component that should handle the intent.
fully qualified class name of the target component
for example "com.example.project.app.FreneticActivity“
Fully qualify name :
package name + class name
com.example.project.app.FreneticActivity
Package name:
Class name:
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com.example.project.app
FreneticActivity
The component name is set by setComponent(), setClass(), or
setClassName() and read by getComponent().
Intent Objects
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Component name,
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The package name or the whole component name is optional.
If it is not used, the system will resolve the target component
using other information.
If it is used however, the specified component will supersede
others information.
Intent Objects
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Action,
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A string naming the action to be performed or,
If broadcast intents, the action that took place and is being
reported.
Intent Objects
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Action,
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The following list is not inclusive,
For more generic predefined actions, see Intent.
Constant
Target component
Action
ACTION_CALL
activity
Initiate a phone call.
ACTION_EDIT
activity
Display data for the user to edit.
ACTION_MAIN
activity
Start up as the initial activity of a task, with no data input and no returned output.
ACTION_SYNC
activity
Synchronize data on a server with data on the mobile device.
ACTION_BATTERY_LOW
broadcast receiver
A warning that the battery is low.
ACTION_HEADSET_PLUG
broadcast receiver
A headset has been plugged into the device, or unplugged from it.
ACTION_SCREEN_ON
broadcast receiver
The screen has been turned on.
ACTION_TIMEZONE_CHANGED
broadcast receiver
The setting for the time zone has changed.
Intent Objects
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Action,
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User defined action for activating the components in your
application is possible,
User defined action should prefix with the application package
name, for example: "com.example.project.SHOW_COLOR".
Intent Objects
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Action,
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The action in an Intent object is set by the setAction() method
and read by getAction().
Intent Objects
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Data
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Each data element can specify a URI and a data type (MIME
media type).
Different actions are paired with different kinds of data
specifications.
Intent Objects
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Data
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Action and data are related
For example,
Action field
inference Data field URI
ACTION_EDIT

URI of the document to be displayed
for editing
ACTION_CALL

tel:
ACTION_VIEW

http:
Intent Objects
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Data
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Related Methods
Method name
Description
setData()
Specifies the data URI
setType()
Specifies the data MIME type
setDataAndType()
Specifies both the data URI and MIME type
getData()
Retrieves the data URI
getType()
Retrieves the data MIME type
Intent Objects
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Category
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A string containing additional information about the kind of
component that should handle the intent.
Constant
Meaning
CATEGORY_BROWSABLE
The target activity can be safely invoked by the browser to display data
referenced by a link — for example, an image or an e-mail message.
CATEGORY_GADGET
The activity can be embedded inside of another activity that hosts gadgets.
CATEGORY_HOME
The activity displays the home screen, the first screen the user sees when
the device is turned on or when the Home button is pressed.
CATEGORY_LAUNCHER
The activity can be the initial activity of a task and is listed in the top-level
application launcher.
CATEGORY_PREFERENCE
The target activity is a preference panel.
See the Intent class description for the full list of categories.
Intent Objects
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Category
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Related methods
Constant
Meaning
addCategory()
places a category in an Intent object
removeCategory()
deletes a category previously added
Intent Objects
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Extras
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Key-value pairs for additional information that should be
delivered to the component handling the intent.
Intent Objects
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Extras
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For example,
ACTION_TIMEZONE_CHANGED intent has a "time-zone" extra
that identifies the new time zone, and
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.
Intent Objects
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Extras
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Related methods
There exist many methods for different extras value types, see
putExtras() and getExtras() for detail.
Intent Objects
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Flags
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Flags of various sorts. Many instruct the Android system how
to launch and treat an activity.
Intent Objects
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Invoking applications that come with the Android
platform
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http://developer.android.com/guide/appendix/g-appintents.html
Browser
Dialer
Google Maps
Google Street view
Intent filters
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Intents can be divided into two groups:
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Explicit intents
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designate the target component by its name.
typically used for application-internal messages.
Implicit intents
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typically used to activate components in other applications.
Intent filters
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For implicit intents
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Android system must resolve the best component (or
components) from the information carried by the intent to
handle request.
Android system does this by comparing the contents of the
Intent object to intent filters of all candidate components.
Intent filters
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Only three entries of an Intent object are consulted when
the object is tested against an intent filter:
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Action
data (both URI and data type)
Category
To start the requested component, all three entries of the
intent have to match the corresponding entries of the
intent filter of the requested component.
Intent filters
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Intent filters
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Component (activities, services, and broadcast receivers) has
set of intent filters that describe its capabilities.†
Implicitly intents are either filtering in or out using these filters.
†Component
without intent filter takes only explicit intent.
Intent filters
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Intent filters
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Activities, services, content provider define theirs’ intent filters
in AndroidManifest.xml †
Broadcast receivers do it differently. It uses
Context.registerReceiver() to create intent filter dynamically.
†The
system has to know the capabilities of these components during installation.
Intent filters
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For example,
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The registerBroadCastReceiver() of ClockBackService.java
/ApiDemos/src/com/example/android/apis/accessibility/Clock
BackActivity.java
private void registerBroadCastReceiver() {
// Create a filter with the broadcast intents we are interested in.
IntentFilter filter = new IntentFilter();
filter.addAction(AudioManager.RINGER_MODE_CHANGED_ACTION);
filter.addAction(Intent.ACTION_SCREEN_ON);
filter.addAction(Intent.ACTION_SCREEN_OFF);
// Register for broadcasts of interest.
registerReceiver(mBroadcastReceiver, filter, null, null);
}
Intent filters
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For example,
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The NoteEditor Activity of Note Pad application sample.
There are two intent filters,
<activity android:name="NoteEditor"
android:theme="@android:style/Theme.Light"
android:label="@string/title_note" >
<intent-filter android:label="@string/resolve_edit">
<action android:name="android.intent.action.VIEW" />
<action android:name="android.intent.action.EDIT" />
<action android:name="com.android.notepad.action.EDIT_NOTE" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="vnd.android.cursor.item/vnd.google.note" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.INSERT" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="vnd.android.cursor.dir/vnd.google.note" />
</intent-filter>
</activity>
starting up with a
specific note that
the user can view
or edit
starting with a new,
blank note that
the user can fill in
and save
Intent filters
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http://developer.android.com/reference/android/content
/Intent.html#ACTION_VIEW
public static final String ACTION_VIEW
Since: API Level 1
Activity Action: Display the data to the user. This is the most common action performed on data -- it is the generic action
you can use on a piece of data to get the most reasonable thing to occur. For example, when used on a contacts entry it
will view the entry; when used on a mailto: URI it will bring up a compose window filled with the information supplied
by the URI; when used with a tel: URI it will invoke the dialer.
Input: getData() is URI from which to retrieve data.
Output: nothing.
Constant Value: “android.intent.action.VIEW“
<activity android:name="NoteEditor"
android:theme="@android:style/Theme.Light"
android:label="@string/title_note" >
<intent-filter android:label="@string/resolve_edit">
<action android:name="android.intent.action.VIEW" />
<action android:name="android.intent.action.EDIT" />
<action android:name="com.android.notepad.action.EDIT_NOTE" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="vnd.android.cursor.item/vnd.google.note" />
</intent-filter>
Intent filters

To start the requested component, all three entries
(Action, Data, and Category) have to be unlocked all
together.
Intent
Requesting
Component
Intent Filter
Action
Requested
Component
Data
Category
This does not mean there is no way that the requested component can be reached.
Do remember, there are other set of intent filters that the requesting component might get through!
Action test
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For example, and intent-filter element with action
subelements
<intent-filter . . . >
<action android:name="com.example.project.SHOW_CURRENT" />
<action android:name="com.example.project.SHOW_RECENT" />
<action android:name="com.example.project.SHOW_PENDING" />
...
</intent-filter>
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a filter must contain at least one <action> element, or all
implicit intents will be blocked.
to pass the filtering, at least one of the <action> element has
to be matched.
Action test
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What if action is missing either in the intent filter or an
intent?
Intriguing….
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If the filter fails to list any actions, no intents can get through
the filter.
If an Intent object doesn't specify an action, it will
automatically passes the test — as long as the filter contains at
least one action.
Category test
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An <intent-filter> element with categories as subelements.
For example:
<intent-filter . . . >
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
...
</intent-filter>

Noticed that, more then one category can be listed inside of
the filter.
Be awarded, only use full qualify name for the element value in the intent filter of the manifest file. However, constant
name can be used in the intend object.
For example, we use android.intent.category.BROWSABLE in the filter (at the manifest file) while
CATEGORY_BROWSABLE is used in the corresponding intent object.
Category test
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Every <category> in the intent has to be matched with one in
the intent filter, but not vice versa.
The intent filter may contain more <category> than an intent.
This says, an Intent object with no categories should always
pass this test, regardless of what's in the filter.
Category test
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Activities that are willing to receive implicit intents must
include "android.intent.category.DEFAULT" in their intent
filters.†
Each intent however, does not have to specify
“android.intent.category.DEFAULT” category when using
startActivity() .
†Filters with "android.intent.action.MAIN" and "android.intent.category.LAUNCHER" settings are the exception. They
can put "android.intent.category.DEFAULT" in the filter but they don’t need to.
Data test
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<data> in the intent filter is contained in a subelement.
<data> in the intent filter can appear multiple times, or not at
all.
For example:
<intent-filter . . . >
<data android:mimeType="video/mpeg" android:scheme="http" . . . />
<data android:mimeType="audio/mpeg" android:scheme="http" . . . />
...
</intent-filter>
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Each <data> element can specify a URI and a data type (MIME
media type).
Data test
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Each <data> element can further divide into a URI and a data
type (MIME media type) entry.
Both URI and data type entries are optional.
Data test
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For URI entry,
The URI contains following parts —
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scheme,
host,
port, and
Data test
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A URI Example,
for each part of the URI:
scheme://host:port/path
content://com.example.project:200/folder/subfolder/etc
scheme
host:port or authority
path
Data test
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For URI
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When the URI in an Intent object is compared to a URI
specification in a filter, only attributes that listed in the filter
matters,
What the gatekeeper(filter) says count!! The visitor(intent
object) has to follow.
For example, if a filter specifies only a scheme, all URIs in the
intent object with that scheme match the filter so on so forth
(kind of redundant.)
Data test
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For URI,
a path specification in the filter can contain wildcards to
require only a partial match of the path.
content://com.example.project:200/folder/subfolder/etc*
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Data test
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For data type entry,
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specifies the MIME type of the data.
can use a "*" wildcard for the subtype field. For example,
"text/*" or "audio/*" — indicating any subtype matches(?
What will a subtype of type text be ?).
Data test
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Matching the data between intent and intent filter.
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In general, for any entry in the filter, there must be a
corresponding matching entry in the intent.
filter
URI
Data type
URI
Data type
intent
Data test
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Matching the data between intent and intent filter.
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For URI like mailto: and tel: which do not refer to actual data,
only matching URI entry in intent and filter is sufficient.
mailto:
tel:
filter
mailto:
tel:
intent
Data test
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Matching the data between intent and intent filter.
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For component that support content: and file:, its filter can
neglect the URI and carry only the data type entry.
The corresponding intent with URI like content: and file: and
matching data type is sufficient.
content:
file:
Data type
filter
Data type
intent
Note Pad Example
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.notepad">
<application android:icon="@drawable/app_notes"
android:label="@string/app_name" >
The first activity,
NotesList consists of
two sets of intent filter.
<provider android:name="NotePadProvider"
android:authorities="com.google.provider.NotePad" />
<activity android:name="NotesList" android:label="@string/title_notes_list">
<intent-filter>
This activity is the main activity of the
<action android:name="android.intent.action.MAIN" />
application. It is the launcher of the
<category android:name="android.intent.category.LAUNCHER" />
application.
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.VIEW" />
Declares things that the activity can
<action android:name="android.intent.action.EDIT" />
do on a directory of notes: VIEW, EDIT,
<action android:name="android.intent.action.PICK" />
PICK.
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="vnd.android.cursor.dir/vnd.google.note" />
</intent-filter>
Note Pad Example
<intent-filter>
<action android:name="android.intent.action.GET_CONTENT" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="vnd.android.cursor.item/vnd.google.note" />
</intent-filter>
</activity>
<activity android:name="NoteEditor"
android:theme="@android:style/Theme.Light"
android:label="@string/title_note" >
<intent-filter android:label="@string/resolve_edit">
<action android:name="android.intent.action.VIEW" />
<action android:name="android.intent.action.EDIT" />
<action android:name="com.android.notepad.action.EDIT_NOTE" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="vnd.android.cursor.item/vnd.google.note" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.INSERT" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="vnd.android.cursor.dir/vnd.google.note" />
</intent-filter>
</activity>
Note Pad Example
<activity android:name="TitleEditor"
android:label="@string/title_edit_title"
android:theme="@android:style/Theme.Dialog">
<intent-filter android:label="@string/resolve_title">
<action android:name="com.android.notepad.action.EDIT_TITLE" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.ALTERNATIVE" />
<category android:name="android.intent.category.SELECTED_ALTERNATIVE" />
<data android:mimeType="vnd.android.cursor.item/vnd.google.note" />
</intent-filter>
</activity>
</application>
</manifest>
Intent filters

Data test


As general rules, when matching intent object to the filter,
What the filter says count. What the filter doesn’t say,
doesn’t matter.
About our final project,
Due date: 18 June, 2012
 Submit a written report + source in a .rar package
1. Title, student ID(s)
2. Introduction
3. Design description (spec., UML drawing, and et c)
4. Implementation (codes segment , run time screenshots)
5. Conclusion
+ APK and source.
and mail to [email protected].
