Jetpack Compose

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

Part 1: Jetpack Compose Basics

5. Decouple Composables

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Previous episode: 4. Add State to Composables Next episode: 6. Build Common UI Components - Part 1

In ui/addBook/AddBookActivity, within AddBookTopBar() composable function, the method onBackPressed() is deprecated and is replaced by onBackPressedDispatcher.onBackPressed() method.

In ui/composeUi/InputField, the statement backgroundColor = Color.White is added to make the background color of OutlinedTextField as white instead of the default theme color.

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Demo

One of the most important things about writing good and clean code is decoupling different components, to make them more reusable.

@Composable
@Preview
fun ActionButton(
  modifier: Modifier = Modifier,
  text: String = "Librarian",
  isEnabled: Boolean = true,
  enabledColor: Color = colorResource(id = R.color.colorPrimary),
  disabledTextColor: Color = Color.Gray,
  onClick: () -> Unit = {}
) {

}

  val backgroundColor = if (isEnabled) enabledColor else Color.LightGray

  TextButton(
    shape = RoundedCornerShape(16.dp),
    enabled = isEnabled,
    colors = ButtonDefaults.textButtonColors(
      backgroundColor = backgroundColor,
      contentColor = Color.White,
      disabledContentColor = disabledTextColor
    ),
    modifier = modifier
      .padding(16.dp),
    content = { Text(text = text) },
    onClick = onClick
  )

@Composable
@Preview
fun BackButton(
  modifier: Modifier = Modifier,
  onBackAction: () -> Unit = {}
) {
  IconButton(
    modifier = modifier,
    content = {
      Icon(
        Icons.Default.ArrowBack,
        tint = Color.White,
        contentDescription = "Back"
      )
    },
    onClick = { onBackAction() }
  )
} 

@Composable
@Preview
fun InputField(
  modifier: Modifier = Modifier,
  value: String = "",
  label: String = stringResource(id = R.string.app_name),
  keyboardType: KeyboardType = KeyboardType.Text,
  isInputValid: Boolean = true,
  imeAction: ImeAction = ImeAction.Next,
  onStateChanged: (String) -> Unit = {}
) {
  val focusedColor = colorResource(id = R.color.colorPrimary)
  val unfocusedColor = colorResource(id = R.color.colorPrimaryDark)

}

  OutlinedTextField(
    value = value,
    onValueChange = { newValue -> onStateChanged(newValue) },
    label = { Text(label) },
    modifier = modifier
      .fillMaxWidth()
      .padding(
        start = 16.dp,
        end = 16.dp,
        top = 4.dp,
        bottom = 4.dp
      ),
    keyboardOptions = KeyboardOptions(keyboardType = keyboardType, imeAction = imeAction),
    visualTransformation = getVisualTransformation(keyboardType),
    isError = !isInputValid,
    colors = ...
  )

colors = TextFieldDefaults.textFieldColors(
      focusedIndicatorColor = focusedColor,
      focusedLabelColor = focusedColor,
      unfocusedIndicatorColor = unfocusedColor,
      unfocusedLabelColor = unfocusedColor,
      cursorColor = focusedColor,
      backgroundColor = Color.White    
    )

private fun getVisualTransformation(keyboardType: KeyboardType) =
  if (keyboardType == KeyboardType.Password || keyboardType == KeyboardType.NumberPassword)
    PasswordVisualTransformation()
  else VisualTransformation.None

@Composable
@Preview
fun TopBar(
  modifier: Modifier = Modifier,
  title: String = "Add a new review",
  actions: @Composable RowScope.() -> Unit = {},
  onBackPressed: (() -> Unit)? = null
) {

}

  val backButtonAction: (@Composable () -> Unit)? = if (onBackPressed != null) {
    @Composable { BackButton(onBackAction = { onBackPressed() }) }
  } else {
    null
  }

  TopAppBar(
    modifier = modifier,
    title = { Text(title) },
    navigationIcon = backButtonAction,
    actions = actions,
    backgroundColor = colorResource(id = R.color.colorPrimary),
    contentColor = Color.White
  )

@Composable
fun AddBookTopBar() {
  TopBar(
    title = stringResource(id = R.string.add_book_title),
    onBackPressed = { onBackPressedDispatcher.onBackPressed() })
}

      InputField(
        value = bookNameState.value,
        onStateChanged = { newValue ->
          bookNameState.value = newValue
          _addBookState.value = _addBookState.value?.copy(name = newValue)
        },
        label = stringResource(id = R.string.book_title_hint)
      )

      InputField(
        value = bookDescriptionState.value,
        onStateChanged = { newValue ->
          bookDescriptionState.value = newValue
          _addBookState.value = _addBookState.value?.copy(description = newValue)
        },
        label = stringResource(id = R.string.book_description_hint)
      )

      ActionButton(
        text = stringResource(id = R.string.add_book_button_text),
        onClick = { onAddBookTapped() }
      )

  @Composable
  fun BooksTopBar() {
    TopBar(
      title = stringResource(id = R.string.my_books_title),
      actions = { FilterButton() })
  }

  @Composable
  fun FilterButton() {
    IconButton(onClick = {
      // TODO
    }) {
      Icon(Icons.Default.Edit, tint = Color.White, contentDescription = "Filter")
    }
  }