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Android uses something called intent filters to track and register apps that can handle certain kinds of intents. Let's see how to specify an intent filter in the Android Manifest.
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At this point, you might be wondering
how the heck does the Google Maps
0:00
app know that we want to show a location.
0:03
And how does the Android system
know if any app can show a location
0:06
on a map or not?
0:09
Well, Android uses something
called intent filters to track and
0:10
register apps that can handle
certain kinds of intents.
0:13
The idea is pretty simple.
0:17
If you want your app to handle
a certain kind of intent,
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either one of the system ones
like this location example, or
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a custom one that you or
another developer creates.
0:23
Then you need to say so
in your apps manifest.
0:26
The Android manifest file contains
all that juicy metadata about
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your app that the operating system and
0:32
Google Play can use to keep track
of which apps do certain things.
0:35
You've actually already seen
intent filters in a manifest.
0:39
We just haven't really
talked in detail about them.
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Let's open up AndroidManifest.xml.
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So it's up here in the manifest folder.
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Double click on it.
0:49
And check out the registration for
MainActivity here.
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It has an element called intent-filter.
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And inside are two children,
action and category.
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This is the standard mean
launcher intent filter
1:02
that specifies which activity
is used to start an app.
1:05
Wait a minute.
1:09
That means that apps
are started by intents.
1:10
Yeah, these things are really
used all over the place.
1:12
Since we don't have a map
viewer in this app,
1:16
let's learn about intent filters
with a different example.
1:18
One of the most common things
to share is simple text data.
1:21
Many apps allow you to share data like,
select text, names, URLs or whatever.
1:24
And many other apps use intent
filters to accept that data and
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do something with it,
like save it or post online.
1:32
For demonstration purposes,
1:35
let's just display the text in
the detail activity somewhere.
1:36
So detail activity is listed
down here at the bottom.
1:40
And inside,
we can add an intent filter element.
1:44
So first, I'm gonna split this into a real
tag with a start and end activity tag.
1:47
Make this line up.
1:54
I'm also gonna add a little
bit of space at the bottom so
1:56
that this bumps up on my screen.
1:58
And we wanna add an intent filter.
2:00
Now, how should we set this?
2:04
Let's take a look at the documentation for
intents and intent filters.
2:07
In the navigation here on the right,
2:11
we see a section called
receiving an implicit intent.
2:12
That's just what we're looking for.
2:15
If we scroll down a little bit,
2:17
we come to a section that lists the three
things we may need for an intent-filter.
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To be specific, we need one or
more of action, data and
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category, depending on
what we're trying to do.
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Pay attention to this
important note right here.
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In order to receive implicit intents,
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you must include the category default
category in the intent-filter.
2:35
We are trying to receive an implicit
intent, so we need to add that.
2:40
We also need an action and
hey, [LAUGH] look at that.
2:43
Down here is an example
of sharing text data.
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It says we need to use
the ACTION_SEND as the action, and
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we can also specify the mime type
of the data with text/plain.
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Mime types can specify text,
images and other types of data.
3:00
So let's add the action.
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Action and
then we say android:name equals,
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android.intent.action.SEND.
3:11
And close this tag and
next we need the default category.
3:15
So we say category,
then we add android:name, and
3:18
this time I will pick from the list,
we want the default category.
3:21
Close this tag and finally for
text, we can add the data, element.
3:26
Then we wanna use android:mimeType and
type text/plain.
3:32
All right.
3:40
Our intent-filter is set.
3:40
At this point,
3:41
if a user wants to share text, our app
will show up as an option for sharing.
3:42
It will launch the DetailActivity but
3:46
nothing would happen because we haven't
actually handled the intent yet.
3:48
All we've done is enable
the routing essentially.
3:51
Let's take a short break and then we'll
add the code to handle the intent.
3:54
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