All language subtitles for 2 - L7 01 Introduction V3 - lang_en

Displaying a list of data is one of the most common UI tasks in Android.

In a weather app, you might show a list of forecasts.

In a chat app, you will show a list of chat messages.

In a news app, you will show a list of news items.

If you look at the apps on your phone,

almost every single app has at least one list.

List vary from a simple list of TextViews that show simple data,

to very complex items that show the user lots of details inside the scrolling list.

Some apps even use a list as their main user interface,

displaying complex summaries for the user to browse.

Some apps use a grid to show a lot of elements in a compact form.

This is a really good pattern that you can communicate effectively with icons or images,

like a photo browsing app.

To support all these use cases,

android comes with the RecyclerView widget.

RecyclerView is designed to be efficient even when displaying extremely large lists.

It allows you to build everything from simple lists of

TextViews all the way to very complex collections of views.

It only support displaying different types of items in the same list.

For example, a news app may want to mix video items into a list of headlines.

RecyclerView is also highly customizable.

Out-of-the-box, it supports lists and grids.

You can configure it to scroll horizontally or vertically.

If the default options aren't enough,

you can even build your own layout manager to make

RecyclerView display any design you dream up.

RecyclerView is efficient in a few ways.

It uses an adapter pattern,

which we will talk about in the next video,

to minimize the work it does when drawing a list.

By default, it will only do work to

process or draw items that are currently visible on the screen.

That means, if your list has 1,000 elements but only 10 are visible,

it will only do enough for it to draw

the first 10 items on screen until the user scrolls.

When the user scrolls,

RecyclerView will figure out what new items should be

on screen and to just enough work to display those.

What's really nice is,

you don't have to do anything to get this behavior.

It comes by default in RecyclerView.

Another way that RecyclerView is efficient is by reusing or recycling as much as it can.

When an item scrolls off the screen, it's recycled.

That means, it will reuse the views it

allocated for the next item that will scroll onto the screen.

It turns out this saves a lot of processing time,

and it helps making sure your list scroll fluidly.

Finally, when an item changes in RecyclerView,

instead of redrawing the entire list,

it just updates that one single item.

This is a huge efficiency gain when displaying lists of complex items.

Recycling as much as possible is key to

making RecyclerView efficient that it's part of the name.

As you'll see in this lesson,

RecyclerView is designed to do this recycling for you.

You don't have to do anything to enable the recycling,

but it does mean you need to be aware that your views will get re-used.

If you don't use the RecyclerView API correctly,

you can extently show old items when the views are reused.

Here, you can see one view that has been filled

and it keeps getting reused by the RecyclerView.

Instead of getting reset when recycled,

it's keeping to fill and showing it on the next item.

We'll talk later in this lesson about how to

use RecyclerView properly when your view is recycled.

RecyclerView, while efficient and customizable,

is not the only way to display a list of things on Androids.

Android also ships with a few other options for displaying lists.

The first are ListView and GridView

for displaying a scrolling list and grid respectively.

You can think of this as RecyclerView simpler,

but less powerful siblings.

Both of them work for displaying a small list of

items that aren't too complex, like 100 items.

They are not nearly as efficient as RecyclerView,

and they don't offer nearly as many options for customizing the display.

In general, the increased performance and flexibility

of RecyclerView makes it a better choice for your app.

The other option is LinearLayout.

You've already seen that earlier linear layout

can be used to display a small list of items,

for example three to five.

But using something as powerful as an RecyclerView is not needed.

However, if you aren't sure that you will ever need to display more than a few elements,

RecyclerView is a better choice.

In this lesson, you will take the sleep tracker app and update it to your RecyclerView.

Last lesson, we'll retrieve and display the scrollable text on-screen.

But wait a minute.

That doesn't look really nice.

The printed concatenated text is very hard to format.

We had to provide a whole pretty complex formatter for it,

and it's almost impossible to have a nice layout design.

For example, we have to show the qualities and number,

and it would look much better as an icon.

Finally, it definitely won't scale as our data grows and changes.

In this lesson, we'll use a recycler view to

show all the sleep data as a simple list like this.

You will implement each part of a RecyclerView,

and we will explain how it works as we go along.

Once you have a working app with a list,

we'll change gears and display the sleep data as a grid.

This is another way to represent the same data,

and we'll see how our RecyclerView architecture helps us easily make updates like this.

At the end of this lesson,

you'll be comfortable using RecyclerView for both lists and grids.

In addition, you will have an understanding of

the adapter pattern used by the RecyclerView.