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When using implicit intents, we are trusting that something in the system will be there to handle the intent. We should be defensive and add an error check, and, if we're really nice, guide the user to a solution.
Below is some example code for how to take a user to Google Play to download an app that can handle a specific kind of Intent. For more information, check out Linking to Your Products on the Android Developer site.
Uri googlePlayUri = Uri.parse("market://search?q=map");
Intent googlePlayIntent = new Intent();
googlePlayIntent.putExtra(Intent.ACTION_VIEW, googlePlayUri);
if (googlePlayIntent.resolveActivity(getPackageManager()) == null) {
Snackbar.make(mRootLayout, "Sorry, nothing found to handle this request.", Snackbar.LENGTH_LONG).show();
}
else {
startActivity(googlePlayIntent);
}
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I'd like to show you something
important about implicit intents.
0:00
We always want to be careful when
we imply anything in case our
0:04
intentions are unclear.
0:07
Remember, communication is hard.
0:08
What I mean is,
what if we didn't have a map installed?
0:11
That probably won't happen for
maps specifically, but
0:14
it could be far more likely with
custom intents which we'll see later.
0:17
We can show this by simply disabling
the maps app in the emulator.
0:22
Let's go to the home screen and
then we'll go into our settings.
0:26
So from here will go into apps and
we'll scroll down a little bit and
0:32
we wanna click on maps and then disable.
0:38
You get a little warning but it's okay,
we wanna just disable the app.
0:43
So now if I switch back to our app,
go to MusicMachine and
0:46
I'll click on the Download button.
0:50
And, no, we got an error.
0:53
Unfortunately, MusicMachine has stopped.
0:55
Okay, let's check log cat
to see what it looks like.
0:57
So if I scroll up a little bit here,
we see the error right away and
1:00
it says no activity found
to handle the intent.
1:04
Like I said, this particular
example is a little contrived.
1:08
But this could happen for
real users in different ways.
1:11
So whenever we use an implicit intent,
it's a good idea to check with Android and
1:14
see if something exists to handle it.
1:17
Let's get rid of log cat.
1:20
We do this by querying something
called the package manager.
1:23
Let's add a line here before
we call start activity.
1:26
We're going to make an if statement and
this is built into the intent class.
1:28
So from our intent,
we can call resolveActivity and
1:32
then getPackageManager.
1:37
This will return null if there
are no activities in the system
1:40
that can handle this kind of intent.
1:44
So I've got parenthese error here but
1:48
that's okay, we want to check if this is
null and then add the other parenthese,
1:50
and in this case we want
to handle the error.
1:54
Otherwise, we are able to resolve it.
2:00
So we do want to call startActivity.
2:01
We'll handle the error by simply
showing a message with a snackbar.
2:04
If you haven't seen a snackbar before,
2:07
they're a lot like toasts except unlike
toasts you can trigger an action.
2:09
Since snackbars are newer, we need to add
a support library in our build.gradle file
2:13
to include them on older
versions of Android.
2:17
So let's open that back up.
2:19
So it's down here in the Gradle scripts.
2:21
Click on the one for the app module and
then here, in the dependencies,
2:23
let's add a new one, compile.
2:27
And then we want
com.android.support:design and
2:31
then the version I have is 23.2.1.
2:38
If you need to download or check your
own version, once again you can use
2:40
the STK manager like we did earlier
to see what you should plug in there.
2:43
Okay, so
let's sync these changes with Gradle.
2:48
And now back in main activity, I'm using
get for this project so I have a warning
2:52
about files that were added, I'm gonna say
Remember, Don't Ask Again and then OK.
2:57
Now back in main activity,
3:03
here where we have the error handling
section, we can add a snackbar.
3:05
Snackbar then we call dot make,
just like we make text with a toast.
3:08
First parameter is the parent view
where this snackbar will be displayed.
3:15
Let's go to our layout file for
main activity.
3:19
Expand res, layout, activity_main.xml and
3:20
the root layout is a relative layout.
3:25
Snackbars work best in
coordinator layouts but
3:29
we can still use them in
a relative layout like this.
3:31
We just need an ID for
the relative layout.
3:33
So I'm going to add one here,
at a line say,
3:36
android:id= And then in parens @+id/.
3:39
Let's call this rootLayout.
3:43
So back here in Main Activity,
let's declare a member variable up top.
3:48
So here somewhere around
out PlaylistAdapter,
3:54
I'm going to say private RelativeLayout.
3:56
And let's call it mRootLayout.
4:00
Let's scroll down to uncreate and
we can add it here.
4:04
We'll say mRootLayout =
cast to a RelativeLayout,
4:08
findViewById R.id.rootLayout.
4:14
Now we can reference it
down in our Snackbar.
4:19
So here where we had the air we
can now pass in mRootLayout And
4:20
then the second parameter is our message.
4:26
Let's say, sorry,
nothing found to handle this request.
4:28
I'm going to add a comma, and then drop
down to new line for the third parameter.
4:36
Which, like a toast, is a duration.
4:40
So let's use snackbar.lengthlong.
4:41
And finally, again like a toast,
we need to show it, so we'll call .show.
4:46
Cool.
4:50
All right, let's see how it looks.
4:51
We'll run it.
4:54
Then tap on download and
there's our snackbar.
5:00
Cool.
5:03
As a side note, if you wanted to direct
users to Google Play to download
5:04
a map app, check the teacher's notes for
more info and some sample code.
5:08
And before we go, let's renewable
Google Maps so we don't forget.
5:12
I'll switch back to settings,
click enable for maps, go back in.
5:16
And this time if I go to download, I
should be able to see the location again.
5:22
All right, cool, it's working.
5:26
See you in the next video.
5:28
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