Jetpack Compose

Oct 11 2022 · Kotlin 1.7.10, Android 13, Android Studio Chipmunk

Part 1: Jetpack Compose Basics

02. Learn About Composable Functions

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Previous episode: 01. Review Android UI Toolkit Next episode: 03. Use Basic Compose Building Blocks

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Notes: 02. Learn About Composable Functions

This course was originally recorded in 2020. It has been reviewed and all content and materials updated as of September 2022.

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Demo

To understand how Jetpack Compose works, it’s best to start from Composable functions and the way Compose renders the UI.

return ComposeView(requireContext()).apply {
  setContent { // new code
    BooksContent() 
  }
}

fun setContent(content: @Composable () -> Unit) {
  shouldCreateCompositionOnAttachedToWindow = true
  this.content.value = content
  if (isAttachedToWindow) {
    createComposition()
  }
}

@Composable
fun BooksContent() {
  Scaffold(topBar = { BooksTopBar() },
    floatingActionButton = { AddNewBook() }) {
   }
}

fun Scaffold(
    modifier: Modifier = Modifier,
    scaffoldState: ScaffoldState = rememberScaffoldState(),
    topBar: @Composable () -> Unit = {},
    bottomBar: @Composable () -> Unit = {},
    snackbarHost: @Composable (SnackbarHostState) -> Unit = { SnackbarHost(it) },
    floatingActionButton: @Composable () -> Unit = {},
    floatingActionButtonPosition: FabPosition = FabPosition.End,
    isFloatingActionButtonDocked: Boolean = false,
    drawerContent: @Composable (ColumnScope.() -> Unit)? = null,
    drawerGesturesEnabled: Boolean = true,
    drawerShape: Shape = MaterialTheme.shapes.large,
    drawerElevation: Dp = DrawerDefaults.Elevation,
    drawerBackgroundColor: Color = MaterialTheme.colors.surface,
    drawerContentColor: Color = contentColorFor(drawerBackgroundColor),
    drawerScrimColor: Color = DrawerDefaults.scrimColor,
    backgroundColor: Color = MaterialTheme.colors.background,
    contentColor: Color = contentColorFor(backgroundColor),
    content: @Composable (PaddingValues) -> Unit
)

@Composable
fun BooksTopBar() {
  TopAppBar(
    title = { Text(stringResource(id = R.string.my_books_title)) },
    backgroundColor = colorResource(id = R.color.colorPrimary),
    contentColor = Color.White
  )
}

fun TopAppBar(
    title: @Composable () -> Unit,
    modifier: Modifier = Modifier,
    navigationIcon: @Composable (() -> Unit)? = null,
    actions: @Composable RowScope.() -> Unit = {},
    backgroundColor: Color = MaterialTheme.colors.primarySurface,
    contentColor: Color = contentColorFor(backgroundColor),
    elevation: Dp = AppBarDefaults.TopAppBarElevation
)

@Composable
fun AddNewBook() {
  FloatingActionButton(
    content = { Icon(Icons.Filled.Add, contentDescription = "Add Book") },
    onClick = {
      showAddBook()
    },
  )
}

fun FloatingActionButton(
    onClick: () -> Unit,
    modifier: Modifier = Modifier,
    interactionSource: MutableInteractionSource = remember { MutableInteractionSource() },
    shape: Shape = MaterialTheme.shapes.small.copy(CornerSize(percent = 50)),
    backgroundColor: Color = MaterialTheme.colors.secondary,
    contentColor: Color = contentColorFor(backgroundColor),
    elevation: FloatingActionButtonElevation = FloatingActionButtonDefaults.elevation(),
    content: @Composable () -> Unit
)