Showing a text field in the app bar in Jetpack Compose with Material3

I came up with a AppBarTextField after some engineering, see the code below. I had to use the lower-level BasicTextField since the normal TextField is not customizable enough. The code having to do with theming and color was copied directly from TextField's implementation, so that the theme's customizations apply normally to the components of the text field.

The parameters the AppBarTextField composable accepts are:

• value: the content string to show in the text field
• onValueChange: new values are passed here (remember to update value!)
• hint: the hint to show when the text field is empty
• modifier, keyboardOptions and keyboardActions: they are passed directly to BasicTextField and they behave the same as they would in a normal TextField. If you need to customize other TextField parameters just add them to the function signature and then pass them to BasicTextField.

The requested features are implemented:

• the focus acquisition was achieved with a SideEffect, so that it would only happen on the first composition
• putting the cursor at the end on the first composition required using a TextFieldValue
• the strange-looking background is not present anymore, since no .background() modifier is present (while it is in the normal TextField)
• the hint was added using by passing a placeholder to TextFieldDecorationBox in the decorationBox parameter (note that this was also possible with TextField)
• TextFieldDecorationBox's padding is also now only 4dp. Padding was added here (and not with a modifier on BasicTextField) since otherwise the bottom line indicator (which is, instead, displayed using the .indicatorLine() modifier) would not be shown correctly.

@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun AppBarTextField(
    value: String,
    onValueChange: (String) -> Unit,
    hint: String,
    modifier: Modifier = Modifier,
    keyboardOptions: KeyboardOptions = KeyboardOptions.Default,
    keyboardActions: KeyboardActions = KeyboardActions.Default,
) {
    val interactionSource = remember { MutableInteractionSource() }
    val textStyle = LocalTextStyle.current
    val colors = TextFieldDefaults.textFieldColors()

    // If color is not provided via the text style, use content color as a default
    val textColor = textStyle.color.takeOrElse {
        MaterialTheme.colorScheme.onSurface
    }
    val mergedTextStyle = textStyle.merge(TextStyle(color = textColor, lineHeight = 50.sp))

    // request focus when this composable is first initialized
    val focusRequester = FocusRequester()
    SideEffect {
        focusRequester.requestFocus()
    }

    // set the correct cursor position when this composable is first initialized
    var textFieldValue by remember {
        mutableStateOf(TextFieldValue(value, TextRange(value.length)))
    }
    textFieldValue = textFieldValue.copy(text = value) // make sure to keep the value updated

    CompositionLocalProvider(
        LocalTextSelectionColors provides LocalTextSelectionColors.current
    ) {
        BasicTextField(
            value = textFieldValue,
            onValueChange = {
                textFieldValue = it
                // remove newlines to avoid strange layout issues, and also because singleLine=true
                onValueChange(it.text.replace("\n", ""))
            },
            modifier = modifier
                .fillMaxWidth()
                .heightIn(32.dp)
                .indicatorLine(
                    enabled = true,
                    isError = false,
                    interactionSource = interactionSource,
                    colors = colors
                )
                .focusRequester(focusRequester),
            textStyle = mergedTextStyle,
            cursorBrush = SolidColor(MaterialTheme.colorScheme.primary),
            keyboardOptions = keyboardOptions,
            keyboardActions = keyboardActions,
            interactionSource = interactionSource,
            singleLine = true,
            decorationBox = { innerTextField ->
                // places text field with placeholder and appropriate bottom padding
                TextFieldDefaults.TextFieldDecorationBox(
                    value = value,
                    visualTransformation = VisualTransformation.None,
                    innerTextField = innerTextField,
                    placeholder = { Text(text = hint) },
                    singleLine = true,
                    enabled = true,
                    isError = false,
                    interactionSource = interactionSource,
                    colors = colors,
                    contentPadding = PaddingValues(bottom = 4.dp)
                )
            }
        )
    }
}

Here is an example usage:

var value by rememberSaveable { mutableStateOf("initial content") }
CenterAlignedTopAppBar(
    title = {
        AppBarTextField(
            value = value,
            onValueChange = { newValue -> value = newValue },
            hint = "A hint..."
        )
    },
    navigationIcon = /* the back icon */,
    actions = /* the search icon */
)