build method

  1. @override
Widget build(
  1. BuildContext context
)
override

Describes the part of the user interface represented by this widget.

The framework calls this method when this widget is inserted into the tree in a given BuildContext and when the dependencies of this widget change (e.g., an InheritedWidget referenced by this widget changes). This method can potentially be called in every frame and should not have any side effects beyond building a widget.

The framework replaces the subtree below this widget with the widget returned by this method, either by updating the existing subtree or by removing the subtree and inflating a new subtree, depending on whether the widget returned by this method can update the root of the existing subtree, as determined by calling Widget.canUpdate.

Typically implementations return a newly created constellation of widgets that are configured with information from this widget's constructor and from the given BuildContext.

The given BuildContext contains information about the location in the tree at which this widget is being built. For example, the context provides the set of inherited widgets for this location in the tree. A given widget might be built with multiple different BuildContext arguments over time if the widget is moved around the tree or if the widget is inserted into the tree in multiple places at once.

The implementation of this method must only depend on:

If a widget's build method is to depend on anything else, use a StatefulWidget instead.

See also:

  • StatelessWidget, which contains the discussion on performance considerations.

Implementation

@override
Widget build(BuildContext context) {
  // We assume ScaleNotifier and CalendarTemplateProvider are available via Provider.
  final scale = context.watch<ScaleNotifier>().scale;
  final templateProvider = context.watch<CalendarTemplateProvider>();
  final theme = Theme.of(context);

  if (templateProvider.isLoading) {
    // Show a compact loader while loading.
    return SizedBox(
        width: 157 * scale,
        height: 25 * scale,
        child: const Center(
            child: SizedBox(
                width: 24,
                height: 25,
                child: CircularProgressIndicator(strokeWidth: 2.0))));
  }

  if (templateProvider.availableTemplates.isEmpty) {
    return const SizedBox.shrink(); // Don't show if no templates exist.
  }

  // Define a consistent text style for the dropdown to reduce font size.
  final TextStyle dropdownTextStyle = TextStyle(
    fontSize: _baseFontSize * scale,
    color: theme.textTheme.bodyLarge?.color,
  );

  return SizedBox(
    width: 157 * scale,
    height: 24 * scale, // Reduced height for a more compact appearance.
    child: DropdownButtonFormField<String>(
      isExpanded: true,
      initialValue: templateProvider.selectedTemplateId,
      style:
          dropdownTextStyle, // Apply style to the selected item and dropdown menu items.
      decoration: InputDecoration(
        // isDense reduces the field's intrinsic height, making it more compact.
        isDense: true,
        // Adjust vertical padding to center the text and icon within the 24px container.
        contentPadding:
            EdgeInsets.symmetric(horizontal: 8 * scale, vertical: 5 * scale),
        border: const OutlineInputBorder(),
      ),
      items: templateProvider.availableTemplates.map((template) {
        return DropdownMenuItem<String>(
          value: template['id'] as String?,
          child: Text(template['name'] as String? ?? 'Unknown',
              overflow: TextOverflow.ellipsis),
        );
      }).toList(),
      // Disable the dropdown while the default template is being updated on the backend.
      onChanged: templateProvider.isUpdatingDefault
          ? null
          : (newTemplateId) {
              if (newTemplateId != null) {
                // Use context.read to call a method inside an event handler like onChanged
                context
                    .read<CalendarTemplateProvider>()
                    .setSelectedTemplateId(newTemplateId);
              }
            },
    ),
  );
}