Jetpack Compose

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

Part 1: Jetpack Compose Basics

6. Build Common UI Components - Part 1

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Previous episode: 5. Decouple Composables Next episode: 7. Build Common UI Components - Part 2

The student materials have been reviewed and are updated as of September 2022.

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Intro

[Slide 1 - Material Design]

Demo

Let’s start off by making more of your components reusable. Open the AddBookActivity. Now let’s move the DropdownMenu from the class to a separate file in the composeUi package, to make it reusable:

@Composable
fun GenrePicker(
  genres: List<Genre>,
  selectedGenreId: String,
  onItemPicked: (Genre) -> Unit
) {
  ...
}

  DropdownMenu(expanded = isGenresPickerOpen.value,
    onDismissRequest = { isGenresPickerOpen.value = false }) {
    for (genre in genres) {
      DropdownMenuItem(onClick = {
        onItemPicked(genre)
        isGenresPickerOpen.value = false
      }) {
        Text(text = genre.name)
      }
    }
  }

GenrePicker(genres = genres, onItemPicked = {
  _addBookState.value = _addBookState.value.copy(genreId = it.id)
}, selectedGenreId = _addBookState.value.genreId ?: "")

private val _addBookState = mutableStateOf(AddBookState())
private val _genresState = mutableStateOf(emptyList<Genre>())	

@Composable
fun BooksContent() {
    val bookFilterDrawerState = rememberBottomDrawerState(initialValue = BottomDrawerValue.Closed)

  Scaffold(topBar = { BooksTopBar(bookFilterDrawerState) },
    floatingActionButton = { AddNewBook(bookFilterDrawerState) }) {
    BookFilterModalDrawer(bookFilterDrawerState = bookFilterDrawerState)
  }
}

@Composable
fun BooksTopBar(bookFilterDrawerState: BottomDrawerState) {
  TopBar(
    actions = { FilterButton(bookFilterDrawerState) })
}

@Composable
fun FilterButton(bookFilterDrawerState: BottomDrawerState) {
  val scope = rememberCoroutineScope()

  IconButton(onClick = {
    scope.launch {
      if (!bookFilterDrawerState.isClosed) {
        bookFilterDrawerState.close()
      } else {
        bookFilterDrawerState.expand()
      }
    }
  }) {
    Icon(Icons.Default.Edit, tint = Color.White, contentDescription = "Filter")
  }
}
               
@Composable
fun AddNewBook(bookFilterDrawerState: BottomDrawerState) {
  val scope = rememberCoroutineScope()

  FloatingActionButton(
    content = { Icon(Icons.Filled.Add, contentDescription = "Add Book") },
    onClick = {
      scope.launch {
        bookFilterDrawerState.close()
        showAddBook()
      }
    },
  )
}

  @ExperimentalMaterialApi
  @Composable
  fun BookFilterModalDrawer(bookFilterDrawerState: BottomDrawerState) {
    val books = _booksState.value ?: emptyList()

    BottomDrawer(
      drawerState = bookFilterDrawerState,
      drawerContent = {
        BookFilterModalDrawerContent(Modifier.align(CenterHorizontally), bookFilterDrawerState)
      },
      content = { BooksList(books) })
  }

@ExperimentalMaterialApi
@Composable
fun BookFilterModalDrawerContent(
  modifier: Modifier,
  bookFilterDrawerState: BottomDrawerState
) {
  val scope = rememberCoroutineScope()
  val genres = _genresState.value ?: emptyList()

  BookFilter(modifier, filter, genres, onFilterSelected = { newFilter ->
    scope.launch {
      bookFilterDrawerState.close()
      filter = newFilter
      loadBooks()
    }
  })
}

@Composable
fun BookFilter(
  modifier: Modifier,
  filter: Filter?,
  genres: List<Genre>,
  onFilterSelected: (Filter?) -> Unit
) {
  val currentFilter = remember {
    mutableStateOf(
      when (filter) {
        null -> 0
        is ByGenre -> 1
        is ByRating -> 2
      }
    )
  } // 0 - no filter, 1 - ByGenre, 2 - By Rating

  val currentGenreFilter = remember { mutableStateOf<Genre?>(null) }
  val currentRatingFilter = remember { mutableStateOf(0) }

Column(
  modifier = modifier,
  horizontalAlignment = Alignment.CenterHorizontally
) {

  Column {
  }
}

Row {
  RadioButton(
    selected = currentFilter.value == 0,
    onClick = { currentFilter.value = 0 },
    modifier = Modifier.padding(8.dp)
  )
  Text(
    text = stringResource(id = R.string.no_filter),
    modifier = Modifier.align(Alignment.CenterVertically)
  )
}

Row {
  RadioButton(
    selected = currentFilter.value == 1,
    onClick = { currentFilter.value = 1 },
    modifier = Modifier.padding(8.dp)
  )

  Text(
    text = stringResource(id = R.string.filter_by_genre),
    modifier = Modifier.align(Alignment.CenterVertically)
  )
}
Row {
  RadioButton(
    selected = currentFilter.value == 2,
    onClick = { currentFilter.value = 2 },
    modifier = Modifier.padding(8.dp)
  )

  Text(
    text = stringResource(id = R.string.filter_by_rating),
    modifier = Modifier.align(Alignment.CenterVertically)
  )
}

val currentlySelectedGenre = currentGenreFilter.value

if (currentFilter.value == 2) {
  RatingBar(
    range = 1..5,
    currentRating = currentRatingFilter.value,
    isLargeRating = true,
    onRatingChanged = { newRating -> currentRatingFilter.value = newRating })
}

if (currentFilter.value == 1) {
  GenrePicker(
    genres = genres,
    selectedGenreId = currentlySelectedGenre?.id ?: "",
    onItemPicked = {
      currentGenreFilter.value = it
    }
  )
}

ActionButton(
  modifier = Modifier.fillMaxWidth(),
  text = stringResource(id = R.string.confirm_filter),
  onClick = {
    val newFilter = when (currentFilter.value) {
      0 -> null
        ...
    }
  }
)

      1 -> ByGenre(currentGenreFilter.value?.id ?: "")
      2 -> ByRating(currentRatingFilter.value)
      else -> throw IllegalArgumentException("Unknown filter!")
    }

    onFilterSelected(newFilter)