Intuitive: Thinking in Compose - MAD Skills

Summary

This video explores Jetpack Compose, a declarative UI framework that contrasts with traditional views. It explains how Compose allows developers to describe UI elements in code using Kotlin, emphasizing state-driven UI updates and recomposition. The example of a survey app illustrates the shift from XML-based views to code-driven UI design.

Takeaways

• 🛠️ Jetpack Compose is a declarative UI framework that simplifies the way developers define their app's user interface by describing what it should contain, not how to achieve it.
• 🔄 The traditional View system requires step-by-step UI construction through XML and Java/Kotlin code, whereas Compose allows UI to be entirely described in Kotlin code, leveraging its full syntax and constructs.
• 📝 Compose eliminates the need for XML by enabling developers to define UI elements directly in code, which can be more intuitive and reduces the context-switching between XML and Kotlin.
• 🔄 In Views, UI state is often managed by manually updating views with setter functions, which can be error-prone and lead to synchronization issues across the app's lifecycle.
• 🔄 Compose handles state changes through recomposition, automatically regenerating the UI when the state changes, reducing the risk of synchronization errors.
• 📱 The script uses a survey app called Jetsurvey as an example to illustrate the differences between building UIs with Views and Compose.
• 📑 In the Views approach, a single component in the UI, like a survey answer, is defined in XML and then manipulated in code, which can become complex with multiple dependent states.
• 🔧 Compose treats UI elements as functions rather than objects, meaning they cannot be mutated directly but are controlled by the state passed to them.
• 🎯 Compose's approach to UI development focuses on 'what' the UI should look like, rather than 'how' to render it, which is a fundamental shift in thinking for developers.
• 🔄 The radio button example in Compose shows how UI elements can be toggled not by holding their own state but by the state values provided to them, demonstrating the 'what, not how' principle.
• 📝 To update UI in Compose, developers use events like 'on click' to change state, which triggers recomposition of the UI elements that depend on that state.
• 🚀 The video promises to cover more advanced topics in future episodes, such as how Kotlin functions work in Compose, the nature of state, and the components available in the framework.

Q & A

What is Jetpack Compose?

Jetpack Compose is a declarative UI framework for building Android apps. It allows developers to describe what the UI should contain, and Compose handles the rest, making it different from traditional views.

How does the UI construction differ in Jetpack Compose compared to traditional views?

In traditional views, UI is constructed step by step through XML and code, defining how each element should look. In Compose, UI is described in code using Kotlin, focusing on what the UI should be rather than how to achieve it.

Why is Compose considered more intuitive to work with?

Compose is more intuitive because it allows developers to describe the UI in a declarative manner, leveraging Kotlin constructs, without the need to manually manage the state and mutations of UI elements.

What is the sample survey app called in the script?

The sample survey app mentioned in the script is called Jetsurvey.

How is a single answer component in a survey app structured in Views?

In Views, a single answer component in a survey app is structured using XML to define elements like an image, text, and a radio button, arranged horizontally. UI state is then populated by obtaining references to these views and calling setter functions.

What are the challenges associated with managing UI state in Views?

Managing UI state in Views can be error-prone as developers need to manually update views when state changes. It's easy to forget to update a view or create conflicts when multiple updates happen simultaneously. Additionally, maintaining state consistency during configuration changes like screen rotations can be complex.

How does Compose handle UI elements differently from Views?

In Compose, UI elements are functions, not objects. They are controlled by the state or arguments passed to them, rather than being mutated through method calls. This approach simplifies the process of updating the UI based on state changes.

What is the process of regenerating the UI when state changes called in Compose?

The process of regenerating the UI when state changes in Compose is called recomposition.

How can the radio button state be updated in Compose?

In Compose, the radio button state is updated through events. When a user interacts with the UI element, an event like 'on click' is emitted, and the event handler can decide to change the UI state, triggering a recomposition of the UI.

What is the role of the 'selected' variable in the Compose example?

In the Compose example, the 'selected' variable is a Boolean that controls the selection state of the radio button. It is passed as an argument to the radio button function and toggled in the 'on click' event handler to update the UI state.

What are the key takeaways from the script about thinking in Compose?

To think in Compose, developers should declare what they want the UI to contain using Kotlin functions, pass in state to control the UI, and use events to update the state, which in turn updates the UI. This approach avoids the need to manually manage UI mutations and makes the development process more intuitive.

Outlines

00:00

🚀 Introduction to Jetpack Compose

The video script introduces Jetpack Compose as a declarative UI framework that simplifies the process of building user interfaces. Unlike traditional views, Compose allows developers to describe the desired UI state without detailing the step-by-step process. This is achieved by leveraging Kotlin's language features to define UI elements directly in code, avoiding the need for XML. The script presents a comparison between building a survey app with Views and Compose, highlighting the intuitive nature of Compose. It also demonstrates the challenges faced when using Views, such as manually updating views upon state changes and the complexity of maintaining state consistency across the app's lifecycle.

05:02

🔄 Compose's Recomposition and State Management

This paragraph delves into the concept of recomposition in Jetpack Compose, which is the process of regenerating the UI when the underlying state changes. It emphasizes the core principle of Compose where state is used to control UI elements, and events are utilized to update the state. The script provides an example of implementing a radio button in Compose, explaining how the state is toggled on user interaction and how this leads to a recomposition of the UI. It also touches on the importance of using special state objects for managing UI state in a production environment, and it concludes with an invitation to learn more about Compose's features, such as Kotlin functions for UI elements and the various components available.

Keywords

💡Jetpack Compose

Jetpack Compose is a declarative UI framework developed by Google for building Android applications. It allows developers to describe the UI in a more intuitive and concise way without having to manage the UI's lifecycle and state manually. In the video, Compose is contrasted with the traditional views system, emphasizing its ability to handle UI updates automatically when the underlying state changes.

💡Declarative UI

A declarative UI framework, as mentioned in the script, is one where developers specify what the UI should look like, rather than how to achieve it. This approach simplifies the development process as it abstracts away the complexities of UI rendering. In the context of the video, Compose's declarative nature is highlighted as a key advantage over the procedural approach required by traditional views.

💡XML

XML, or Extensible Markup Language, is a markup language used to define the structure of documents and data. In Android development, XML has traditionally been used to define the layout of user interfaces. The video script discusses how Compose eliminates the need for XML by allowing UI to be described entirely in Kotlin code.

💡Kotlin

Kotlin is a statically typed programming language that runs on the Java Virtual Machine and is interoperable with Java. It is now the preferred language for Android development. In the video, Kotlin is used to demonstrate how UI can be declared in code with Compose, taking advantage of its features and constructs.

💡UI Elements

UI elements refer to the individual components that make up a user interface, such as buttons, text fields, and images. The script explains that in Compose, UI elements are defined as functions rather than objects, which is a fundamental shift from the traditional views system.

💡State

State in the context of UI development refers to the data that influences the UI's appearance and behavior. The video emphasizes the importance of state in Compose, where UI elements are controlled by the state passed to them, rather than holding their own state internally.

💡Recomposition

Recomposition is the process in Compose where the UI is automatically updated when the state changes. This is a core concept in the framework, as it allows for a reactive UI that responds to state changes without manual intervention. The script illustrates how recomposition simplifies the development of dynamic UIs.

💡Event Handling

Event handling is the process of responding to user interactions with the UI, such as clicks or touches. In Compose, event handlers can update the state, which in turn triggers recomposition of the UI. The video script uses the example of a radio button's on-click event to demonstrate how state can be toggled in response to user interaction.

💡Survey App

The script uses the example of a 'Jetsurvey' app to illustrate the concepts of building UIs with Compose. A survey app typically requires dynamic UI updates based on user input, making it a relevant example to demonstrate the benefits of Compose's declarative approach and state management.

💡Configuration Change

A configuration change in Android development refers to events like screen rotations or changes in device orientation that can affect the UI state. The video script mentions the challenges of maintaining UI state across configuration changes when using traditional views, whereas Compose simplifies this process by managing state more effectively.

💡Android Developers Channel

The Android Developers Channel is a resource mentioned in the script for viewers to find more content related to Compose and Android development. It serves as a platform for educational content and updates on best practices and new features in Android development.

Highlights

Jetpack Compose is a declarative UI framework that simplifies UI development by handling the 'how' after you describe the 'what'.

Compose differs from traditional views by allowing UI to be entirely described in Kotlin code, eliminating the need for XML.

The declarative nature of Compose makes it more intuitive by focusing on describing UI elements rather than the step-by-step construction.

In Views, UI elements are defined in XML and manipulated in code, requiring references and setter functions to update the UI state.

Compose avoids the complexity of manually updating views when state changes, reducing the potential for errors and bugs.

State management in Compose is more straightforward, as UI updates are triggered by state changes without the need for explicit view mutations.

Compose's approach to UI elements as functions, rather than objects, simplifies the process of passing state to control the UI.

Recomposition in Compose is the process of regenerating the UI when state changes, which is central to its operation as a UI framework.

The example of a survey app called Jetsurvey demonstrates the practical application of Compose for building interactive UIs.

In Compose, UI elements are controlled by the state passed to them, rather than holding their own state that changes due to user events.

Updating state in Compose is achieved through events, such as on-click, which can trigger changes in the UI state.

The video provides a step-by-step guide on how to build a component in Compose, emphasizing the shift in thinking from Views to Compose.

Compose's handling of state and events simplifies the development of interactive UIs, such as enabling a 'Next' button based on user selection.

The video outlines the process of toggling a radio button's selection state in Compose, demonstrating the use of state variables and event handlers.

Compose's approach to UI development promotes a cleaner, more maintainable codebase by abstracting away the complexities of view manipulation.

The video promises to delve deeper into the workings of Compose, including its Kotlin functions, state management, and available components, in future episodes.

The Android Developers Channel encourages viewers to like, share, and subscribe for more educational content on Compose and other Android development topics.

Transcripts

CHRIS ARRIOLA: Jetpack Compose is a declarative UI framework.

You describe what your UI should contain,

and Compose handles the rest.

This way of writing UI is very different from views.

In this video, we'll cover the difference between the two

and how you can shift your thinking

to build apps with Compose.

[MUSIC PLAYING]

With Views, you describe step by step

how to get your UI to look a certain way.

You do this by defining UI in XML,

finding views from XML in code, and then calling

setter functions to get your UI to look the way you want.

With Compose, you no longer have to write XML.

UI can entirely be described in code in Kotlin,

taking full advantage of Kotlin constructs.

Constructing UI by describing what, not how,

is a key difference between Compose and Views.

It's what makes Compose much more intuitive to work with.

Let's take a look at a sample survey app called Jetsurvey.

The screen shows a single choice question

the user has to answer.

Once they make a selection, they can then

proceed to the next question.

To understand how to think about building this in Compose,

let's first look at how we might build this using Views.

To simplify things, we'll look at a single component

in the screen.

A single answer in the survey.

This component is composed of an image, some text,

and a radio button all arranged horizontally.

In Views, these elements would all be defined in XML.

To populate the views with UI state,

we would have to obtain a reference

to each view in Kotlin or Java in our fragment

or activity using findViewById.

After obtaining references, we would then mutate each view

by calling setter functions like setImage or setText

to display the desired UI state.

When state changes, for example, when a user selects an answer,

the view that was interacted with would appear selected.

In our example, when a user selects

an answer in the question, we also

want the Next button to be enabled.

So if we want other views to update

as a side effect of a view being selected,

we would have to set a listener to that view,

and explicitly mutate other affected views.

But having to manually update views when

state changes is error prone.

It's possible to forget to update a view

with its dependent state.

And it's also easy to create a legal status

when multiple updates conflict in unexpected ways.

What if your app goes through a configuration

change like a screen rotation?

And in the process, you might correctly

remember the selection from the user.

But you might forget to re-enable the Next button.

Synchronizing state changes throughout the lifespan

of an app is a recurring challenge

when working with Views.

This problem also increases in complexity

as the number of views and dependent states

grow in your app.

It's a solvable problem.

But it's a common source of bugs.

Let's switch gears and see how we

can think about building this component in Compose.

In Compose, we would construct the UI in a similar fashion--

in a container arranged horizontally

with an image, text, and a radio button.

Instead of writing this in XML, we would define our elements

directly in code, in Kotlin.

Doing it this way, we no longer have

to jump between XML and code as the UI would already

be declared in code.

In Compose, UI elements are functions, and not objects.

This means you can't find a reference to them,

and call methods to mutate them.

Instead, UI elements are entirely

controlled by the state or arguments that you pass.

Here, we are just describing what our UI should look like.

No calls to find view by ID, setImage, or setText.

Our UI is described succinctly in the functions

we are calling.

To display the UI state that we want,

we're passing the answer's properties to the image

function, to the text function, and for now let's

just pass false to the radio button function

which shows it as unselected.

Another important distinction here from Views

is that tapping this answer will not show the item as selected.

This is because we're always providing false to the radio

button, meaning that it will stay unselected regardless

of user interaction.

Unlike in Views, the radio button

doesn't hold its own state that automatically

changes due to a user event.

But rather, the radio button state

is controlled by the values that are provided into it.

This is what we mean by what, not how.

We're declaring what our UI should

look like by providing the necessary states

where our UI functions.

But we're not telling Compose how

it should render that state.

So if state controls the UI, how do we

go about updating state to update the UI?

In Compose, we do that through events.

When a user interacts with the UI element,

the UI emits an event such as on click.

And the event handler can then decide if the UI

state should be changed.

If UI state changes, the functions, or UI elements,

that depend on that state will be re-executed.

This process of regenerating the UI when state changes is

called recomposition.

The process of converting state into UI and state changes

causing UI to regenerate is at the core of how Compose

works as a UI framework.

Let's revisit our example and update our implementation

so that the radio button gets toggled when it's clicked.

First, let's define a Boolean variable called selected,

and pass that into the radio button function argument.

Next, in on click event handler, let's

change the selected value to be the opposite

of its current value.

This way, when it's clicked, it toggles the selection state.

With this change, we should now see the radio button being

toggled when clicking on it.

Notice that I left out the implementation

of the select variable because for this to work,

we have to use a special state object, which

we'll cover in the next video.

In a production app, the state of the radio button

should come from the answer state object.

But we kept it like this to showcase

how radio button state works.

To summarize, to think in Compose,

we declare what we want our UI to contain,

but we don't tell it step by step how to do it.

Unlike views.

We use Kotlin functions to represent our UI elements.

We pass in state to control UI.

And we use events to update state,

which in turn updates our UI.

This was a really high level overview

of how to think in Compose.

But there's so much more to learn.

For instance, how do these Kotlin functions work?

What does state look like?

What are the different components provided in Compose?

We'll answer those questions in the upcoming episodes.

Check out the resources below to learn more.

If you like this video, go ahead and like, share,

and subscribe to the Android Developers Channel

to see more videos on Compose.

I'll see you in the next episode.

[MUSIC PLAYING]