c# - 如何在保存特定月份天数列表的组合框的选择更改时显示下个月的天数

Question

我有 2 个组合框。第一个组合框显示月份，第二个组合框显示所选月份的日期。

假设选择的月份是 Jan，选择的日期是 31。现在如果用户单击键盘向下箭头，则应该显示下一天。即月组合应该选择二月和日组合应该选择1。我怎样才能做到这一点？

当用户更改月份时，我将绑定所选月份的实际天数。我没有找到当用户尝试越过组合框限制时会触发的正确事件。即当用户在第 31 天单击向下箭头时，我如何跟踪组合框值的限制是否越过，以便我可以填充下个月的日期？

Answer 1

一个想法是在天组合框中添加一个额外且不可见的天，并在选择它时更改所选月份。

这是您的 viewModel（您的视图的数据上下文）

public class ViewModel : DependencyObject
{
    public ViewModel()
    {
        for (int i = 0; i < 12; i++)
        {
            Months.Add(new Month(i+1, 31, this));//this is simplified
        }
        SelectedMonth = Months.First();
    }
    //Months Observable Collection
    private ObservableCollection<Month> _months = new ObservableCollection<Month>();
    public ObservableCollection<Month> Months { get { return _months; } }
    //SelectedMonth Dependency Property
    public Month SelectedMonth
    {
        get { return (Month)GetValue(SelectedMonthProperty); }
        set { SetValue(SelectedMonthProperty, value); }
    }
    public static readonly DependencyProperty SelectedMonthProperty =
        DependencyProperty.Register("SelectedMonth", typeof(Month), typeof(ViewModel), new UIPropertyMetadata(null));
}

这是你的月课

public class Month : DependencyObject
{
    public Month(int number, int count, ViewModel parent)
    {
        _parent = parent;
        Number = number;
        Days.Add(new Day { IsLastDayOfMonth = false, IsFirstDayOfMonth = true });
        for (int i = 0; i < count; i++)
        {
            Days.Add(new Day { 
                Number = i + 1, 
                IsLastDayOfMonth = false, 
                IsFirstDayOfMonth = false });
        }
        Days.Add(new Day { IsLastDayOfMonth = true, IsFirstDayOfMonth = false });
        SelectedDay = Days[1];//first is empty so by default day1 is selected
    }
    ViewModel _parent;

    //Number Dependency Property
    public int Number
    {
        get { return (int)GetValue(NumberProperty); }
        set { SetValue(NumberProperty, value); }
    }
    public static readonly DependencyProperty NumberProperty =
        DependencyProperty.Register("Number", typeof(int), typeof(Month), new UIPropertyMetadata(1));

    //Days Observable Collection
    private ObservableCollection<Day> _days = new ObservableCollection<Day>();
    public ObservableCollection<Day> Days { get { return _days; } }

    //SelectedDay Dependency Property
    public Day SelectedDay
    {
        get { return (Day)GetValue(SelectedDayProperty); }
        set { SetValue(SelectedDayProperty, value); }
    }
    public static readonly DependencyProperty SelectedDayProperty =
        DependencyProperty.Register("SelectedDay", typeof(Day), typeof(Month),
        new UIPropertyMetadata(null, (d, e) =>
        {
            var viewModel = ((Month)d)._parent;
            if (((Day)e.NewValue).IsLastDayOfMonth)
            {
                var selMonth = viewModel.Months.FirstOrDefault(x => x.Number == ((Month)d).Number + 1);
                if (selMonth == null || selMonth.Number == 1) return;
                viewModel.SelectedMonth = selMonth;
                viewModel.SelectedMonth.SelectedDay =
                    viewModel.SelectedMonth.Days[1];//first real day of month
            }
            else if (((Day)e.NewValue).IsFirstDayOfMonth)
            {
                var selMonth = viewModel.Months.FirstOrDefault(x => x.Number == ((Month)d).Number - 1);
                if (selMonth == null) return;
                viewModel.SelectedMonth = selMonth;
                viewModel.SelectedMonth.SelectedDay = 
                    viewModel.SelectedMonth.Days[
                    viewModel.SelectedMonth.Days.Count - 2];//last real day of month
            }
        }));
}

这是你的日课

    //Number Dependency Property
    public int Number
    {
        get { return (int)GetValue(NumberProperty); }
        set { SetValue(NumberProperty, value); }
    }
    public static readonly DependencyProperty NumberProperty =
        DependencyProperty.Register("Number", typeof(int), typeof(Day), new UIPropertyMetadata(1));
    //IsLastDayOfMonth Dependency Property
    public bool IsLastDayOfMonth
    {
        get { return (bool)GetValue(IsLastDayOfMonthProperty); }
        set { SetValue(IsLastDayOfMonthProperty, value); }
    }
    public static readonly DependencyProperty IsLastDayOfMonthProperty =
        DependencyProperty.Register("IsLastDayOfMonth", typeof(bool), typeof(Day), new UIPropertyMetadata(false));
    public bool IsFirstDayOfMonth
    {
        get { return (bool)GetValue(IsFirstDayOfMonthProperty); }
        set { SetValue(IsFirstDayOfMonthProperty, value); }
    }
    public static readonly DependencyProperty IsFirstDayOfMonthProperty =
        DependencyProperty.Register("IsFirstDayOfMonth", typeof(bool), typeof(Day), new UIPropertyMetadata(false));

这是你的 xaml：

    <ComboBox ItemsSource="{Binding SelectedMonth.Days}"
              SelectedItem="{Binding SelectedMonth.SelectedDay}">
        <ComboBox.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding Number}" x:Name="textblock"/>
                <DataTemplate.Triggers>
                    <DataTrigger Binding="{Binding IsLastDayOfMonth}" Value="True">
                        <Setter TargetName="textblock" Property="Visibility" Value="Collapsed"/>
                    </DataTrigger>
                </DataTemplate.Triggers>
            </DataTemplate>
        </ComboBox.ItemTemplate>
    </ComboBox>