Flutter DateTimeRange

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Flutter时间段选择控件的界面优化过程

需求描述

Flutter默认提供的时间段选择组建调用如下:

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DateTimeRange? pickedRange = await showDateRangePicker(
       context: context,
       initialDateRange: DateTimeRange(
           start: DateTime.now().subtract(Duration(days: 30)),
           end: DateTime.now()),
       helpText: "选择领料日期段",
       cancelText: '取消',
       saveText: '确认',
       firstDate: DateTime.now().subtract(Duration(days: 365)),
       lastDate: DateTime.now()
   );

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从效果图来看并不让人满意，需要修改的地方有:
1.背景
2.helpText字体大小
3.跨年的情况下未完全显示的时间段，即时间段字体大小

修改过程

按照原生开发的思路，首先直接找构造属性，没有再通过获取实例动态修改，但是flutter的view是Widget，其呈现和和更新机制和原生不同，先按照一般思路往下操作

一般思路

直接在构造方法中查看是否有配置属性就可以了，通过属性修改即可，查看showDateRangePicker方法源码:

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Future<DateTimeRange?> showDateRangePicker({
  required BuildContext context,
  DateTimeRange? initialDateRange,
  required DateTime firstDate,
  required DateTime lastDate,
  DateTime? currentDate,
  DatePickerEntryMode initialEntryMode = DatePickerEntryMode.calendar,
  String? helpText,
  String? cancelText,
  String? confirmText,
  String? saveText,
  String? errorFormatText,
  String? errorInvalidText,
  String? errorInvalidRangeText,
  String? fieldStartHintText,
  String? fieldEndHintText,
  String? fieldStartLabelText,
  String? fieldEndLabelText,
  Locale? locale,
  bool useRootNavigator = true,
  RouteSettings? routeSettings,
  TextDirection? textDirection,
  TransitionBuilder? builder,
}) async {...//省略

并没有helpText相关的style设置，也就是说并没有属性能够配置，看来该方法不可行

查看源码

当一般方法行不通的时候就需要一点点探究精神了，既然这个Widget的显示中有字体，就一定有字体相关的style属性，同理也一定是在哪里设置了颜色相关配置，那就简单了，直接源码看一下哪里赋值的不就知道了么
直接查找”date_picker.dart”源码类中的 Widget build(BuildContext context) 行,就能找到Widget构建的地方，也就能在这里找到属性的赋值了

先说字体:1313-1336行

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case DatePickerEntryMode.calendarOnly:
  contents = _CalendarRangePickerDialog(
    key: _calendarPickerKey,
    selectedStartDate: _selectedStart.value,
    selectedEndDate: _selectedEnd.value,
    firstDate: widget.firstDate,
    lastDate: widget.lastDate,
    currentDate: widget.currentDate,
    onStartDateChanged: _handleStartDateChanged,
    onEndDateChanged: _handleEndDateChanged,
    onConfirm: _hasSelectedDateRange ? _handleOk : null,
    onCancel: _handleCancel,
    entryModeButton: showEntryModeButton
      ? IconButton(
          //编辑按钮图标
          icon: const Icon(Icons.edit),
          padding: EdgeInsets.zero,
          color: onPrimarySurface,
          tooltip: localizations.inputDateModeButtonLabel,
          onPressed: _handleEntryModeToggle,
        )
      : null,
    confirmText: widget.saveText ?? localizations.saveButtonLabel,
    helpText: widget.helpText ?? localizations.dateRangePickerHelpText,
  );

源码这里IconButton就是我们的日期展示后面的编辑按钮，那么前面的部分就有设置字体大小的地方，前面是一个_CalendarRangePickerDialog，进入源码查看一下 1457-1475行

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@override
Widget build(BuildContext context) {
  final ThemeData theme = Theme.of(context);
  final ColorScheme colorScheme = theme.colorScheme;
  final MaterialLocalizations localizations = MaterialLocalizations.of(context);
  final Orientation orientation = MediaQuery.of(context).orientation;
  final TextTheme textTheme = theme.textTheme;
  final Color headerForeground = colorScheme.brightness == Brightness.light
      ? colorScheme.onPrimary
      : colorScheme.onSurface;
  final Color headerDisabledForeground = headerForeground.withOpacity(0.38);
  final String startDateText = _formatRangeStartDate(localizations, selectedStartDate, selectedEndDate);
  final String endDateText = _formatRangeEndDate(localizations, selectedStartDate, selectedEndDate, DateTime.now());
  //这下面就是设置开始和结束的时间，那这个headlineStyle就是字体大小了
  final TextStyle? headlineStyle = textTheme.headline5;
  final TextStyle? startDateStyle = headlineStyle?.apply(
      color: selectedStartDate != null ? headerForeground : headerDisabledForeground,
  );
  final TextStyle? endDateStyle = headlineStyle?.apply(
      color: selectedEndDate != null ? headerForeground : headerDisabledForeground,
  );
  final TextStyle saveButtonStyle = textTheme.button!.apply(
      color: onConfirm != null ? headerForeground : headerDisabledForeground,
  );

成功找到headline的style设置来源于textTheme.headline5,说明这些属性是通过Theme的属性设置的,那是不是给我们的日期选择dialog外面加一个Theme并配置相关属性就可以了呢？是的，就是这么简单，但还需要找到属性的对应关系，也就是说应该配置哪些属性。这里有两个问题 1.怎么包装这个dialog，2.找剩余需要配置的属性

1.怎么包装这个dialog

很显然要拿到这个dialog的widget才行，所以再次后去看showDateRangePicker的源码1007-1023行

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if (locale != null) {
  dialog = Localizations.override(
    context: context,
    locale: locale,
    child: dialog,
  );
}

return showDialog<DateTimeRange>(
  context: context,
  useRootNavigator: useRootNavigator,
  routeSettings: routeSettings,
  useSafeArea: false,
  builder: (BuildContext context) {
      //这里会判断是否有builder，如果有，则使用builder来封装dialog
    return builder == null ? dialog : builder(context, dialog);
  },
);

还记得showDateRangePicker的属性TransitionBuilder? builder吗？是的，可以通过设置builder来获取到该dialog，再包装一层Theme就解决了

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    DateTimeRange? pickedRange = await showDateRangePicker(
        context: context,
        initialDateRange: DateTimeRange(
            start: DateTime.now().subtract(Duration(days: 30)),
            end: DateTime.now()),
        helpText: "选择领料日期段",
        cancelText: '取消',
        saveText: '确认',
        firstDate: DateTime.now().subtract(Duration(days: 365)),
        lastDate: DateTime.now()
        builder: (context, child) => customDatePickTheme(context,child)
    ); 

    customDatePickTheme(context, child) {
        ThemeData theme = Theme.of(context);
    return Theme(
        data: theme,
        child: Container(
            child: child,));
}

2.其他属性的查找

使用上面的方法查找属性在1506-1514行,找到helpText的字体大小由textTheme.overline设置

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child: Column(
    crossAxisAlignment: CrossAxisAlignment.start,
    children: <Widget>[
        Text(
        helpText,
        style: textTheme.overline!.apply(
            color: headerForeground,
        ),
        ),

查看_HighlightPainter类即选中的时间段颜色在_buildDayItem中2247-2254行

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Widget _buildDayItem(BuildContext context, DateTime dayToBuild, int firstDayOffset, int daysInMonth) {
  final ThemeData theme = Theme.of(context);
  final ColorScheme colorScheme = theme.colorScheme;
  final TextTheme textTheme = theme.textTheme;
  final MaterialLocalizations localizations = MaterialLocalizations.of(context);
  final TextDirection textDirection = Directionality.of(context);
  //这里设置选中的颜色
  final Color highlightColor = _highlightColor(context);
  final int day = dayToBuild.day;
  ...略

  //可以看出选中颜色由Theme的colorScheme控制
  Color _highlightColor(BuildContext context) {
      return Theme.of(context).colorScheme.primary.withOpacity(0.12);
  }

总结

阅读源码并不难，只要根据自己的需求抓主要线索就能很快定位到需要查找的地方，这比引入一个新控件节省更多的时间和学习成本，下次遇到其他修改需求也能更快的找到并修改，最后贴一下DateTimeRange的Theme配置和效果图

image

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DateTimeRange? pickedRange = await showDateRangePicker(
    context: context,
    initialDateRange: DateTimeRange(
        start: DateTime.now().subtract(Duration(days: 30)),
        end: DateTime.now()),
    helpText: "选择日期段",
    cancelText: '取消',
    saveText: '确认',
    firstDate: DateTime.now().subtract(Duration(days: 365)),
    lastDate: DateTime.now()
    builder: (context, child) => customDatePickTheme(context,child)
);

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//日期选择的主题和字体大小设置
customDatePickTheme(context, child) {
  ThemeData theme = Theme.of(context);
  final TextTheme partialTheme = TextTheme(
      headline4: TextStyle(fontSize: ScreenUtil().setSp(30)),
      headline5: TextStyle(fontSize: ScreenUtil().setSp(30)),
      overline: TextStyle(fontSize: ScreenUtil().setSp(36)));
  theme = theme.copyWith(
      colorScheme:
          theme.colorScheme.copyWith(primary: AppBarColors.backgroundColor),
      textTheme: theme.textTheme.merge(partialTheme),
      appBarTheme: AppBarTheme(
        backgroundColor: AppBarColors.backgroundColor,
      ));
  return Theme(
      data: theme,
      child: Container(
        child: child,
      ));
}