Flutter-如果日期（今天）相同，则DatePicker无法打开

Question

我只想在日历中从星期几开始启用星期五。如果日期不是同一天（例如，如果当前日期不是星期五，那么它正在工作），那么它将正常工作；否则，如果我尝试在星期五打开日历，那么我将获得以下例外。

[ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: 'package:flutter/src/material/date_picker.dart': Failed assertion: line 1147 pos 5: 'selectableDayPredicate == null || selectableDayPredicate(initialDate)': Provided initialDate must satisfy provided selectableDayPredicate

下面是我正在使用的代码。

DateTime selectedDate = DateTime.now();

    bool defineSelectable(DateTime val) {
      DateTime now = DateTime.now();
      // disabled all days before today
      if (val.isBefore(now)) {
        return false;
      }
      // disabled all days except Friday
      switch (val.weekday) {
        case DateTime.friday:
          return true;
          break;
        default:
          return false;
      }
    }

    int daysToAdd(int todayIndex, int targetIndex) {
      print('todayIndex $todayIndex');
      print('targetIndex $targetIndex');
      if (todayIndex < targetIndex) { // jump to target day in same week
        return targetIndex - todayIndex;
      } else if (todayIndex > targetIndex) { // must jump to next week
        return 7 + targetIndex - todayIndex;
      } else {
        return 0; // date is matched
      }
    }

    DateTime defineInitialDate() {
      DateTime now = DateTime.now();
      int dayOffset = daysToAdd(now.weekday, DateTime.friday);
      print('dayOffset: $dayOffset');
      return now.add(Duration(days: dayOffset));
    }

    Future<Null> _selectDate(BuildContext context) async {
      print('defineInitialDate: ${defineInitialDate()}');
      print('defineSelectable: $defineSelectable');
      final DateTime picked = await showDatePicker(
          context: context,
          initialDate: defineInitialDate(),
          selectableDayPredicate: defineSelectable,
          firstDate: DateTime(2018, 12),
          lastDate: DateTime(2020, 12));
      if (picked != null && picked != selectedDate) selectedDate = picked;
      var formatter = DateFormat('EEEE, dd-MMMM-yyyy');
      String formatted = formatter.format(selectedDate);
      print('Select Date: $formatted');
      _askGiveProvider.meetingSink(formatted);
      //addEventBloc.eventDateSink(formatted);
    }

不知道到底是什么问题。如果您能告诉我需要更新哪些内容，那就太好了。

而且我也想从当前日期起仅启用2周。我该如何实现？

谢谢。

Answer 1

这里是解决方案您需要使defineSelectable函数在您传递的intail.date返回true。参见下面的工作代码

DateTime selectedDate = DateTime.now();
DateTime initialData;

bool defineSelectable(DateTime val) {
DateTime now = DateTime.now();
//make it return true on initialDate
if(val.compareTo(initialData)==0){
return true;
}
// disabled all days before today
if (val.isBefore(now)) {
return false;
}
// disabled all days except Friday
switch (val.weekday) {
case DateTime.friday:
  return true;
  break;
default:
  return false;
}
}

int daysToAdd(int todayIndex, int targetIndex) {
print('todayIndex $todayIndex');
print('targetIndex $targetIndex');
if (todayIndex < targetIndex) { // jump to target day in same 
week
return targetIndex - todayIndex;
} else if (todayIndex > targetIndex) { // must jump to next 
week
return 7 + targetIndex - todayIndex;
} else {
return 0; // date is matched
}
}

DateTime defineInitialDate() {
DateTime now = DateTime.now();
int dayOffset = daysToAdd(now.weekday, DateTime.friday);
print('dayOffset: $dayOffset');
return now.add(Duration(days: dayOffset));
}

Future<Null> _selectDate(BuildContext context) async {
initialData = defineInitialDate();
print('defineInitialDate: ${initialData}');
print('defineSelectable: $defineSelectable');
final DateTime picked = await showDatePicker(
  context: context,
  initialDate: initialData,
  selectableDayPredicate: defineSelectable,
  firstDate: DateTime(2018, 12),
  lastDate: DateTime(2020, 12));
if (picked != null && picked != selectedDate) selectedDate = 
picked;
//var formatter = DateFormat('EEEE, dd-MMMM-yyyy');
//String formatted = formatter.format(selectedDate);
print('Select Date: $selectedDate');
//_askGiveProvider.meetingSink(formatted);
//addEventBloc.eventDateSink(formatted);
}

Answer 2

尝试一下，这不会更改日期后的今天的日期

  DateTime selectedDate = DateTime.now();
  DateTime initialData;

  bool defineSelectable(DateTime val) {
    DateTime now = DateTime.now();
    // disabled all days except Friday
    switch (val.weekday) {
      case DateTime.friday:
        return true;
        break;
      default:
        return false;
    }

  }

  int daysToAdd(int todayIndex, int targetIndex) {
    print('todayIndex $todayIndex');
    print('targetIndex $targetIndex');
    if (todayIndex < targetIndex) { // jump to target day in same week
      return targetIndex - todayIndex ;
    } else if (todayIndex > targetIndex) { // must jump to next week
      return 7 + targetIndex - todayIndex ;
    } else {
      return 0; // date is matched
    }
  }

  DateTime defineInitialDate() {
    DateTime now = DateTime.now();
    int dayOffset = daysToAdd(now.weekday, DateTime.friday);
    print('dayOffset: $dayOffset');
    return now.add(Duration(days: dayOffset));
  }

  Future<Null> _selectDate(BuildContext context) async {
    initialData = defineInitialDate();
    print('defineInitialDate: ${defineInitialDate()}');
    print('defineSelectable: $defineSelectable');
    final DateTime picked = await showDatePicker(
        context: context,
        initialDate: initialData,
        selectableDayPredicate: defineSelectable,
        firstDate: DateTime(2018, 12),
        lastDate: DateTime(DateTime.now().year, DateTime.now().month, DateTime.now().day + 14));
    if (picked != null && picked != selectedDate) selectedDate = picked;
    var formatter = DateFormat('EEEE, dd-MMMM-yyyy');
    String formatted = formatter.format(selectedDate);
    print('Select Date: $formatted');
//    _askGiveProvider.meetingSink(formatted);
    //addEventBloc.eventDateSink(formatted);
  }