showMaterialBanner method

ScaffoldFeatureController<MaterialBanner, MaterialBannerClosedReason> showMaterialBanner(
  1. MaterialBanner materialBanner
)

Shows a MaterialBanner across all registered Scaffolds. Scaffolds register to receive material banners from their closest ScaffoldMessenger ancestor. If there are several registered scaffolds the material banner is shown simultaneously on all of them.

A scaffold can show at most one material banner at a time. If this function is called while another material banner is already visible, the given material banner will be added to a queue and displayed after the earlier material banners have closed.

To remove the MaterialBanner with an exit animation, use hideCurrentMaterialBanner or call ScaffoldFeatureController.close on the returned ScaffoldFeatureController. To remove a MaterialBanner suddenly (without an animation), use removeCurrentMaterialBanner.

See ScaffoldMessenger.of for information about how to obtain the ScaffoldMessengerState.

Here is an example of showing a MaterialBanner when the user presses a button.
link

To create a local project with this code sample, run:
flutter create --sample=material.ScaffoldMessengerState.showMaterialBanner.1 mysample

Implementation

ScaffoldFeatureController<MaterialBanner, MaterialBannerClosedReason> showMaterialBanner(MaterialBanner materialBanner) {
  assert(
    _scaffolds.isNotEmpty,
    'ScaffoldMessenger.showMaterialBanner was called, but there are currently no '
    'descendant Scaffolds to present to.',
  );
  _materialBannerController ??= MaterialBanner.createAnimationController(vsync: this)
    ..addStatusListener(_handleMaterialBannerStatusChanged);
  if (_materialBanners.isEmpty) {
    assert(_materialBannerController!.isDismissed);
    _materialBannerController!.forward();
  }
  late ScaffoldFeatureController<MaterialBanner, MaterialBannerClosedReason> controller;
  controller = ScaffoldFeatureController<MaterialBanner, MaterialBannerClosedReason>._(
    // We provide a fallback key so that if back-to-back material banners happen to
    // match in structure, material ink splashes and highlights don't survive
    // from one to the next.
    materialBanner.withAnimation(_materialBannerController!, fallbackKey: UniqueKey()),
    Completer<MaterialBannerClosedReason>(),
        () {
      assert(_materialBanners.first == controller);
      hideCurrentMaterialBanner();
    },
    null, // MaterialBanner doesn't use a builder function so setState() wouldn't rebuild it
  );
  setState(() {
    _materialBanners.addLast(controller);
  });
  _updateScaffolds();
  return controller;
}