c# - DatePicker 抛出可见性异常

Question

我在自己的 View 中添加了一个 DatePicker，但我收到了 Visibility 属性的错误消息(我尚未配置)。

错误是:

System.Windows.Data Error: 'MS.Internal.Data.DynamicValueConverter' converter failed to convert value '8/18/1993' (type 'System.String'); BindingExpression: Path='DateOfBirth' DataItem='Gui.ViewModels.RegisterPersonalViewModel' (HashCode=64515557); target element is 'Microsoft.Phone.Controls.DatePicker' (Name='DateOfBirth'); target property is 'Visibility' (type 'System.Windows.Visibility').. System.ArgumentException: Requested value '8/18/1993' was not found.
   at System.Enum.EnumResult.SetFailure(ParseFailureKind failure, String failureMessageID, Object failureMessageFormatArgument)
   at System.Enum.TryParseEnum(Type enumType, String value, Boolean ignoreCase, EnumResult& parseResult)
   at System.Enum.Parse(Type enumType, String value, Boolean ignoreCase)
   at MS.Internal.SilverlightTypeConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value)
   at MS.Internal.Data.DefaultValueConverter.ConvertHelper(Object o, Type destinationType, CultureInfo culture, Boolean isForward)
   at MS.Internal.Data.TargetDefaultValueConverter.Convert(Object o, Type type, Object parameter, CultureInfo culture)
   at MS.Internal.Data.DynamicValueConverter.Convert(Object value, Type targetType, Object parameter, CultureInfo culture)
   at System.Windows.Data.BindingExpression.ConvertToTarget(Object value). 

View 字段如下所示:

<toolkit:DatePicker x:Name="DateOfBirth" />

以及 View 模型中的属性:

public DateTime DateOfBirth { get; set; }

因此，我没有将 Visibility 属性映射到该字段的任何内容。那么它为什么要进行绑定(bind)呢？

我还尝试添加这样的可见性绑定(bind):

<toolkit:DatePicker x:Name="DateOfBirth"
                       Visibility="{Binding Path=IsDateOfBirthVisible,
                                    Converter={StaticResource BooleanToVisibilityConverter}}"/>

并添加一个字段:

public DateTime DateOfBirth { get; set; }
public bool IsDateOfBirthVisible { get; set; }

但随后我得到以下异常:

An exception of type 'System.Exception' occurred in System.Windows.ni.dll and wasn't handled before a managed/native boundary

我还尝试添加自定义约定:

ConventionManager.AddElementConvention<DatePicker>(DateTimePickerBase.ValueProperty, "Value", "SelectedDate");
ConventionManager.AddElementConvention<DatePicker>(DateTimePickerBase.ValueStringFormatProperty, "ValueStringFormat", "ValueStringFormatChanged");
ConventionManager.AddElementConvention<DatePicker>(DateTimePickerBase.ValueStringProperty, "ValueString", "ValueStringChanged");
ConventionManager.AddElementConvention<DatePicker>(UIElement.VisibilityProperty, "Visibility", "VisibilityChanged");

但这并没有什么不同。

我是 Caliburn 和 Windows Phone 的新手，所以某处可能有一个愚蠢的错误。

如何摆脱该异常？

(日期选择器来自 https://phone.codeplex.com/)

Answer 1

Caliburn.Micro 在 FrameworkElement 上定义了一个“包罗万象”的惯例它将您在 View 模型上的匹配属性绑定(bind)到 FrameworkElement.VisibilityProperty

AddElementConvention<FrameworkElement>(
    FrameworkElement.VisibilityProperty, "DataContext", "Loaded");

因为 Caliburn.Micro 不知道 Microsoft.Phone.Controls.DatePicker类型或其基类( DateTimePickerBase ， Control )它回退到 FrameworkElement约定，它会尝试绑定(bind)您的 DateTime到 DatePicker VisibilityProperty所以您会在“输出”窗口中看到异常。

有两种解决方法:

• 手写绑定(bind):<toolkit:DatePicker Value="{Bidning DateOfBirth}" />

• 创建自定义约定，在本例中为:

  ConventionManager.AddElementConvention<DatePicker>(
       DateTimePickerBase.ValueProperty, "Value", "SelectedDate");
  

  注意:给定类型只能有一个约定，因此这应该是您的唯一 AddElementConvention<DatePicker>打电话。