Struct MaterialBanner 

pub struct MaterialBanner<Msg = Callback> { /* private fields */ }

A message across the top of the screen with the actions that answer it.

It sits in the flow, not over it: a banner is put above the content it is about, usually as the first child of a screen’s column. Nothing hides it on a timer, which is the whole difference from a snack bar — an action does.

Implementations

impl<Msg: Clone + 'static> MaterialBanner<Msg>

pub fn new(content: impl Into<String>) -> Self

A banner saying content. Add at least one action: a banner stays until one is taken, and the reference makes them required for that reason.

pub fn with_content(content: impl Widget<Msg> + 'static) -> Self

The same, with a widget in place of the text.

pub fn leading(self, leading: impl Widget<Msg> + 'static) -> Self

A glyph before the message.

pub fn action(self, action: impl Widget<Msg> + 'static) -> Self

Adds an action. One action sits on the message’s own line; two or more take a line of their own (banner.dart:348).

pub fn force_actions_below(self, force: bool) -> Self

Puts the actions on a line of their own even when there is only one.

pub fn content_text_style(self, style: TextStyle) -> Self

What the message is set in. bodyMedium by default.

pub fn background(self, color: Color) -> Self

The banner’s colour. A low container tone by default.

pub fn surface_tint(self, color: Color) -> Self

What the surface is tinted towards for its elevation. Unset, nothing is — the reference’s Material 3 answer (banner.dart:513).

pub fn shadow_color(self, color: Color) -> Self

The shadow’s colour. Unset, there is none.

pub fn divider_color(self, color: Color) -> Self

The rule along the bottom, which is drawn only when the banner is flat — see Self::elevation.

pub fn elevation(self, elevation: f32) -> Self

How far off the page it sits. 0 by default — see BANNER_ELEVATION.

It decides two other things, which is why it is worth naming: a banner off the page keeps a 10-pixel margin under it so its shadow has room, and a banner flat on the page draws a rule along its bottom edge instead (banner.dart:425). Height or a line, never both — the same either-or Card makes between a shadow and a hairline.

pub fn padding(self, padding: Insets) -> Self

The padding around the message row.

pub fn margin(self, margin: Insets) -> Self

The margin around the banner.

pub fn leading_padding(self, padding: Insets) -> Self

What the leading slot is held off the message by.

pub fn min_action_bar_height(self, height: f32) -> Self

The shortest the actions bar gets. 52 by default.

pub fn build(self) -> Box<dyn Widget<Msg>>

Assembles the banner.

Deferred to a ThemeBuilder: whether the actions sit on the message’s line decides which children exist and in what order, and the padding and the rule are the theme’s to answer, so the composition cannot happen before the theme is known.