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In this video we start looking at what Anko's doing behind the scenes!
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We've just used the magic of Anko
to create our entire layout and
0:00
side our activity.
0:04
But what's really going on
behind the scenes here?
0:05
To get a better look let's get rid of
everything inside a relative layout,
0:09
and then let's take a deep dive
into the inner workings of Anko,
0:15
starting with this
relative layout function.
0:19
Let's start by getting rid
of the brackets, as well and
0:21
then adding parentheses so
we can see what the parameters really are.
0:26
The first parameter is an integer
representing which theme we're using.
0:31
And it defaults to zero.
0:35
We won't be using a theme for this app,
so we'll be omitting the theme parameter.
0:37
The second parameter is
a function named init.
0:43
This is the code that will be used
to initialize the relative layout.
0:46
And it will be an extension function
on the _relativeLayout class
0:50
which returns nothing.
0:54
Wait, did he say _relativeLayout?
0:57
Sure did, on the next line let's
type underscore, relative layout.
1:00
And then use command or
control + B to go to the declaration.
1:07
Here we can see that
underscore relative layout
1:11
extends the regular relative layout class.
1:14
It then goes on to declare a few different
versions of the l params function.
1:18
Let's take a look at the second one.
1:28
First off if you're not
familiar with generics.
1:31
That's what's going on
here with this letter T.
1:34
In this function T can be
any class that extends view.
1:38
So lparams is an extension function
on any class that extends view.
1:43
And inside this function,
first we create the layout params
1:49
by using the width and height attributes
which defaults to wrap content.
1:54
Then, we initialize those layout params
using the init function we passed in
2:00
and next,
we add those layoutParams to our view.
2:06
And remember this is of
type t which extends view.
2:11
And finally, we return the view.
2:16
Cool, right?
2:19
This whole class is just to make it so
that we have an easier time
2:21
of setting layout params for
the views and our relative layouts.
2:24
In fact, the point of this entire file
2:29
is just to add the L primes extension
function to the views, and our layouts.
2:32
It's just a bunch of different
underscore layout, extends layout.
2:38
And then all the different l
params functions for that layout.
2:46
Also I don't think I've mentioned it yet
but
2:52
classes in Collin are closed by default.
2:54
So if you want to be
able to extend the class,
2:58
you need to declare that class as open.
3:00
Okay, now that we know that underscore
relative layout is just a relative layout
3:04
with some extra lparams functions,
let's get back to main activity and
3:09
the relative layout function.
3:14
Let's delete the underscore relative
layout line and then let's take another
3:17
look at the parameters to this
relative layout function.
3:21
It looks like there is one version of this
function with only a theme as a parameter
3:25
and another version that takes on
both a theme and an init function.
3:30
And it looks like each of these
versions is declared twice.
3:35
What's up with that?
3:39
Let's use command or
control + B to jump to the declaration and
3:41
see what's happening.
3:44
And here we can see that both versions
of our relative layout function,
3:47
the one that takes in only a theme and
the one that takes in both a theme and
3:51
an init function, are declared as
extension functions on the activity class.
3:55
But if we double click on relative
layout and then use command or
4:00
control + F to find each occurrence.
4:04
It becomes clear that both versions of our
relative layout function are declared as
4:08
extension functions on each of the view
manager, context, and activity classes.
4:13
So since main activity
is both an activity and
4:19
a context because the activity
extends from context,
4:22
when we call the relative layout function
it could be any of these four functions.
4:27
Okay, now let's dig a little bit deeper.
4:33
What actually happens when
we call this function?
4:36
And since these are the same two functions
let's just look at the activity ones.
4:39
First we've got the version
that only takes in a theme.
4:49
This is the version we're currently using.
4:53
When we call relative layout
without passing in any parameters
4:55
we're calling this function
which gives us a theme of zero.
4:59
And then calls the second relative layout
function while passing in that theme and
5:03
an empty init function.
5:08
The second relative layout function
5:10
then takes a relative layout
constant along with our theme and
5:13
an if function and passes them on
to a new function called ankoView.
5:18
But before we move on to Anko view, let's
look at that relative layout constant.
5:23
Let's use command or
control + B to jump to its declaration.
5:28
And here we can see that relative
layout is just an anonymous function
5:34
which takes in a context and returns
an instance of underscore relative layout.
5:38
Which remember, is just a relative layout
with some extra lparams functions.
5:43
All right, now let's scroll back down
to the relative layout function, And in
5:48
the next video, we'll finish our deep dive
by jumping into the Anko view function.
5:55
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