CalendarDatePicker绑定空值

本文关键字：空值 绑定 CalendarDatePicker | 更新日期: 2023-09-27 18:09:36

我正在使用CalendarDatePicker

<CalendarDatePicker x:Name="DatePick" DisplayMode="Decade" Date="{Binding DisplayValue, Mode=TwoWay}"/>

问题是当我绑定日期属性时，选择器不再显示默认占位符文本(选择日期)，而是现在显示01.1.1916，如果属性为空(属性总是设置为空)。

public DateTimeOffset? DisplayValue {get;set;}

如果我手动将null作为Date的值，它现在会再次显示PlaceholderText。

DatePick.Date=null;

并且绑定仍然有效/我在选择日期时获得所需的值。那么是否有可能显示占位符文本而不使用隐藏代码?

CalendarDatePicker绑定空值

似乎calendardatepicker "min value"总是当前年份小于100，我已经修改了你的代码在我这边:

  public class CalendarDatePickerEx : CalendarDatePicker
  {
    public DateTimeOffset? DefaultValue { get; set; }
    public static readonly DependencyProperty DefaultValueProperty =
      DependencyProperty.Register("DefaultValue", typeof(DateTimeOffset), typeof(CalendarDatePickerEx), new PropertyMetadata(null, (sender, e) =>
      {
        if ((DateTimeOffset?)e.NewValue != null && ((CalendarDatePickerEx)sender).Date.Value.Date.Year == DateTime.Today.Year - 100)
        {
          ((CalendarDatePickerEx)sender).SetDisplayDate((DateTimeOffset)e.NewValue);
          ((CalendarDatePickerEx)sender).Date = null;
        }
        else if ((DateTimeOffset?)e.NewValue == null && ((CalendarDatePickerEx)sender).Date.Value.Date.Year == DateTime.Today.Year - 100)
        {
          {
            ((CalendarDatePickerEx)sender).SetDisplayDate(DateTimeOffset.Now);
            ((CalendarDatePickerEx)sender).Date = null;
          }
        }
      }));
  }

首选的解决方案

如果您使用x:Bind而不是Binding，则一切正常，并且如果绑定的日期值为空，您可以看到占位符。

直接在XAML页面中:

<CalendarDatePicker Date="{x:Bind DataContext.DisplayValue, Mode=TwoWay}"/>

或在DataTemplate内:

<DataTemplate x:Key="DateFieldItemTemplate"
              x:DataType="DataModel:ObjectTypeWithDate">
    <Grid>
        <CalendarDatePicker Date="{x:Bind DateField, Mode=TwoWay}"/>
    </Grid>
</DataTemplate>

我找到了一个可行的解决方案。因此，我扩展了默认的calendarDatePicker。我添加了一个额外的可绑定属性，它既可以作为选择日期的defaultValue Setter，也可以在需要时作为日期值的Setter。

public class CustomNewCalendarDatePicker : CalendarDatePicker
{
public DateTimeOffset? DefaultValue { get; set; }
public static readonly DependencyProperty DefaultValueProperty =
  DependencyProperty.Register("DefaultValue", typeof(DateTimeOffset), typeof(CustomNewCalendarDatePicker), new PropertyMetadata(null, (sender, e) =>
  {
    if ((DateTimeOffset?)e.NewValue != null && ((CustomNewCalendarDatePicker)sender).Date.Value.Date.Year == 1916)
    {
      ((CustomNewCalendarDatePicker)sender).SetDisplayDate((DateTimeOffset)e.NewValue);
      ((CustomNewCalendarDatePicker)sender).Date = null;
    }
    else if ((DateTimeOffset?)e.NewValue == null && ((CustomNewCalendarDatePicker)sender).Date.Value.Date.Year == 1916)
    {
      {
        ((CustomNewCalendarDatePicker)sender).SetDisplayDate(DateTimeOffset.Now);
        ((CustomNewCalendarDatePicker)sender).Date = null;
      }
    }
  }));
}

我的解决方案，它对我来说很好

public class CalendarDatePickerExt : CalendarDatePicker
{
    public CalendarDatePickerExt()
    {
        this.DateChanged += CalendarDatePickerExt_DateChanged;
    }
    private void CalendarDatePickerExt_DateChanged(CalendarDatePicker sender, CalendarDatePickerDateChangedEventArgs args)
    {
        if (args.NewDate != null && args.NewDate.Value.Year == DateTime.Today.Year - 100)
        {
            this.SetDisplayDate(DateTimeOffset.Now);
            this.Date = null;
        }
    }
}

在具有属性的类中，您需要实现INotifyPropertyChanged接口。在属性DisplayValue中，你必须调用onPropertyChanged-method。

示例代码:Xaml: 

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <CalendarDatePicker x:Name="DatePick" DisplayMode="Decade" Date="{Binding DisplayValue, Mode=TwoWay}"/>
</Grid>

MainPage.cs: 

public sealed partial class MainPage : Page
{
    public MainPage()
    {
        this.InitializeComponent();
        ViewModel viewModel = new ViewModel();
        DataContext = viewModel;
    }
}
自定义类(ViewModel): 
class ViewModel : INotifyPropertyChanged
    {
        private DateTimeOffset _displayValue;
        public DateTimeOffset? DisplayValue
        {
            get
            {
                return _displayValue;
            }
            set
            {
                if (value != null) _displayValue = value.Value;
                OnPropertyChanged();
            }
        }
        public ViewModel()
        {
            DisplayValue = new DateTimeOffset(2016, 9, 29, 6, 39, 10, 3, new TimeSpan());
        }


        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
相关文章：