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You have completed Intents and Broadcast Receivers!
You have completed Intents and Broadcast Receivers!
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Intents come in two varieties: Explicit and Implicit. We use explicit intents when we explicitly name the class of the target activity that will handle the intent. Implicit intents are used without a class name, where Android will help determine an appropriate Activity to handle the intent.
I forgot to include a new app icon in the initial project files! If you want to use it, download it here, delete the default icons here in your mipmap folder, and then put the new icon file in there.
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Let's start with one of the most common
scenarios we encounter in Android,
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passing data from one activity to another.
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If you've been taking other courses here,
then you've already seen this, of course.
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But let's take a deeper look at
what Android is doing for us, so
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we can better understand how intents work
and the different ways we can use them.
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A quick note.
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I forgot to include a new app icon
in the initial project files.
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If you want to use it, download it from
the teacher's notes, delete the default
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icons here in the res > mipmap folder,
and then put the new icon file in here.
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All right, so
let's close this build.gradle file and
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open up MainActivity.
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So expand Java and then the package and
double click on it.
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Now for this brief exercise, let's
hijack the code in our download button.
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So I'm gonna scroll down a little bit and
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we have an OnClickListener here in the
OnCreate method for our download button.
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I'll start by refactoring
this code into a method.
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So I'm going to select everything,
right click on it,
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then refactor, Extract into a Method.
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Make sure we select MainActivity,
not an anonymous method.
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And let's call this downloadSongs.
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Hit Enter.
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And okay, so now it's down at the bottom.
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Our code was collapsed.
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I'll just click on it to expand it and
a space and
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I'm going to comment this code out for
now.
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Let's create a new method in
here to simply test intents.
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Now if we go back to this method and
use Alt+Enter, our quick fix,
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we can create this new method.
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And once again select MainActivity.
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And here we go we have a new method stub.
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In here all we want to do
is create a new intent.
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Let's call it intent.
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And then we'll use the constructor new
Intent that expresses our intent to
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start a new activity which needs the
current contexts as the first parameter.
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And the name of the target activity as the
second parameter, DetailActivity.class.
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Now to start this activity, we call
startActivity and pass in this new intent.
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So let's try this out just to
make sure that it's working.
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Okay, here's app and
since we hijacked the download button.
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Let's tap on that.
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All right, and here's our second activity.
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So let's take another look at this code.
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This intent, where we name the class
that's going to handle it,
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is known as an explicit intent.
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Let's take a quick look at some of the
documentation on the Android Developer's
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site about intents.
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If we scroll down just a little bit,
we see a section here on intent types.
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There are two types of intents,
explicit intents and implicit intents.
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So here in explicit, note that it says
you'll typically use an explicit intent to
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start a component in your own app because
you know the class name of the activity or
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service you want to start.
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So right back here,
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we are explicitly using the class
name of the target activity.
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So what do you think it means
to use an implicit intent?
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What intent would we imply without
explicitly using a known class?
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This is where the true power and
beauty of intents comes into play.
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This is something I love about Android.
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We can use intents to easily
leverage other parts of Android, or
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other apps, to help us do things
in the context of our own app.
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Intents change our device from
a grab bag of independent apps
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to a system of integrated components.
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What I really mean is this.
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Implicit intents allow us to imply
a solution to handling an intent
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without explicitly defining what
is going to handle that intent.
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In other words, we say we wanna do
something without knowing exactly
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how to do it, but trusting the Android
system to help us figure it out.
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Or if we take a look at the definition in
the docs, we declare a general action to
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perform which allows a component
from another app to handle it.
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This then goes on to use an example of
showing a specific location on a map.
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We don't need to create an activity or
write special code to show a location.
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Most Android devices have some kind
of map app on them, like Google Maps.
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And if we use an implicit intent to
show it, the Android system will present
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the user with a list of options that
can display a location on a map.
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As always, this is best
explained with a real example.
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We'll come back to that
in a little bit though.
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Let's stick with explicit intents for
a little while longer and
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learn next how to pass data back and
forth between two activities.
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