build method

  1. @override
Widget build (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).

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) {
  final ThemeData themeData = Theme.of(context);
  final MaterialLocalizations localizations = MaterialLocalizations.of(context);
  final int year = displayedMonth.year;
  final int month = displayedMonth.month;
  final int daysInMonth = getDaysInMonth(year, month);
  final int firstDayOffset = _computeFirstDayOffset(year, month, localizations);
  final List<Widget> labels = <Widget>[
    ..._getDayHeaders(themeData.textTheme.caption, localizations),
  ];
  for (int i = 0; true; i += 1) {
    // 1-based day of month, e.g. 1-31 for January, and 1-29 for February on
    // a leap year.
    final int day = i - firstDayOffset + 1;
    if (day > daysInMonth)
      break;
    if (day < 1) {
      labels.add(Container());
    } else {
      final DateTime dayToBuild = DateTime(year, month, day);
      final bool disabled = dayToBuild.isAfter(lastDate)
          || dayToBuild.isBefore(firstDate)
          || (selectableDayPredicate != null && !selectableDayPredicate(dayToBuild));

      BoxDecoration decoration;
      TextStyle itemStyle = themeData.textTheme.body1;

      final bool isSelectedDay = selectedDate.year == year && selectedDate.month == month && selectedDate.day == day;
      if (isSelectedDay) {
        // The selected day gets a circle background highlight, and a contrasting text color.
        itemStyle = themeData.accentTextTheme.body2;
        decoration = BoxDecoration(
          color: themeData.accentColor,
          shape: BoxShape.circle,
        );
      } else if (disabled) {
        itemStyle = themeData.textTheme.body1.copyWith(color: themeData.disabledColor);
      } else if (currentDate.year == year && currentDate.month == month && currentDate.day == day) {
        // The current day gets a different text color.
        itemStyle = themeData.textTheme.body2.copyWith(color: themeData.accentColor);
      }

      Widget dayWidget = Container(
        decoration: decoration,
        child: Center(
          child: Semantics(
            // We want the day of month to be spoken first irrespective of the
            // locale-specific preferences or TextDirection. This is because
            // an accessibility user is more likely to be interested in the
            // day of month before the rest of the date, as they are looking
            // for the day of month. To do that we prepend day of month to the
            // formatted full date.
            label: '${localizations.formatDecimal(day)}, ${localizations.formatFullDate(dayToBuild)}',
            selected: isSelectedDay,
            sortKey: OrdinalSortKey(day.toDouble()),
            child: ExcludeSemantics(
              child: Text(localizations.formatDecimal(day), style: itemStyle),
            ),
          ),
        ),
      );

      if (!disabled) {
        dayWidget = GestureDetector(
          behavior: HitTestBehavior.opaque,
          onTap: () {
            onChanged(dayToBuild);
          },
          child: dayWidget,
          dragStartBehavior: dragStartBehavior,
        );
      }

      labels.add(dayWidget);
    }
  }

  return Padding(
    padding: const EdgeInsets.symmetric(horizontal: 8.0),
    child: Column(
      children: <Widget>[
        Container(
          height: _kDayPickerRowHeight,
          child: Center(
            child: ExcludeSemantics(
              child: Text(
                localizations.formatMonthYear(displayedMonth),
                style: themeData.textTheme.subhead,
              ),
            ),
          ),
        ),
        Flexible(
          child: GridView.custom(
            gridDelegate: _kDayPickerGridDelegate,
            childrenDelegate: SliverChildListDelegate(labels, addRepaintBoundaries: false),
            padding: EdgeInsets.zero,
          ),
        ),
      ],
    ),
  );
}