Component Architecture

The Jetpack Compose SDK exposes three types of components:

• Screen components: out-of-the-box, screen-sized Composables.
• Bound components: Composables bound to our ViewModels for state handling.
• Stateless components: low-level, stateless Composables for full customizability.

Let’s go through each type to see what the difference is and how to use them.

Screen Components

Complete screen solutions that connect all the operations you need to give users a Chat experience.

These components are very easy to use and they display entire screens for you with default behavior. They allow you to explore the SDK features in a breeze, however, they offer limited customization.

We have two screen components:

• ChannelsScreen: Builds a screen that shows a header with user information, the list of channels for the current user and a search input to filter those channels by name.
• MessagesScreen: Builds a full chat experience with a header that shows information about the channel, list that supports messages (including attachments, reactions, replies, threads and more) and a message composer that lets you write messages and send attachments.

Usage

To use either the ChannelsScreen or the MessagesScreen component within your Activity or Fragment, you just need to call it within setContent():

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    setContent {
        ChatTheme { // Theme wrapper
            ChannelsScreen(
                title = stringResource(id = R.string.app_name),
                onItemClick = {
                    // On item clicked action
                },
                onHeaderActionClick = {
                    // Header header action clicks
                },
                onHeaderAvatarClick = {
                    // Handle header avatar clicks
                },
                onViewChannelInfoAction = {
                    // Show UI to view more info about channel
                },
                onBackPressed = { finish() }
            )
        }
    }
}

This will give you a fully working screen:

Channel List (Light Theme)	Channel List with Open Channel Menu (Light Theme)

Channel List (Dark Theme)	Channel List with Open Channel Menu (Dark Theme)

You can learn more about ChannelsScreen and MessagesScreen on their respective pages.

Bound Components

These components serve a specific use-case and are bound to a ViewModel. The ViewModel provides the components with data and handles input events that the components send.

These components display UI for a portion of the screen and are more customizable than Screen components.

They usually represent features on the screen like the header, input, search field, menu or a list of data. Some of these components are:

• MessageList: Connects to the API using the ViewModel, shows a list of messages or empty or loading states, handles pagination, single and long item taps and more.
• ChannelList: Same as the MessageList, but for channels.
• MessageComposer: Holds an input field to write new messages in, allows you to send attachments and shows different states when replying to or editing a message.
• AttachmentsPicker: Allows you to pick and choose from system media, files or media capture to send attachments.

Usage

These components are great because you can combine them with any other UI you build to form custom screens. Again, to use the components, all you need to do is call them within setContent() in your Activity or Fragment:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    // Your ViewModel instance
    val channelListViewModel: ChannelListViewModel by viewModels { ... }

    setContent {
        ChatTheme { // Theme wrapper
            ChannelList(
                modifier = Modifier.fillMaxSize(),
                viewModel = channelListViewModel,
                onChannelClick = {
                    // Open the MessagesScreen
                },
            )
        }
    }
}

You can build these components in two ways:

• Providing an instance of our ViewModel yourself - this lets you control the lifecycle of the VM or customize the behavior of your UI by calling functions directly on the VM.
• Using the default argument for the ViewModel - this is less work, but you can’t control the lifecycle of the VM, nor can you call functions on it to support custom behavior.

Either way, these components connect all the required operations related to them and they expose more customization as you can override both behavior and UI, like the items in the list. The snippet above will produce the following screen:

Light Theme	Dark Theme

You can combine this component with your custom UI, with other components from the SDK or use it on its own. You can learn more about each of these components in the Compose UI Components section.

Stateless Components

These are pure components that rely on external state and expose various events you can handle yourself. These components don’t depend on a ViewModel, allowing you to decide where the data comes from.

They offer fully customizable behavior as well as customizable UI where it makes sense. Some of these components are:

• Avatar: Shows an image provided as a parameter in a shape defined by the ChatTheme. Fully customizable in terms of size, shape, alignment and more.
• SearchInput: Shows a leading icon for search, an input field to write your query and a trailing icon to clear the input. The leading icon can be fully customized, as well as the listeners for state changes.
• MessageList and ChannelList: We offer stateless alternatives to some ViewModel powered components if you don’t want to use our ViewModel and want to customize the behavior, as well as the UI.
• MessageComposer: A stateless alternative not backed by a ViewModel. Useful if you want more control over the component.

Usage

These components don’t do much on their own and they require state to render. You can use them like before, by calling them in setContent(), but they require more parameters to set up:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    setContent {
        var queryState by remember { mutableStateOf("") } // The query state

        SearchInput(
            query = queryState, // Connect the value to the state holder
            modifier = Modifier
                .fillMaxWidth()
                .padding(vertical = 32.dp, horizontal = 24.dp), // Customize the looks
            onValueChange = {
                queryState = it // Change the value when typing
            }
        )
    }
}

As you can see, these components are still fairly easy to use, but do require instructions on what state they show and how they look. This snippet will produce the following UI:

Search Input (Light Theme)

Search Input (Dark Theme)

You can customize the component to add a background, touch event handlers, elevation and more.