Question

在程序中，我有一个DatePicker，允许用户不输入日期。但是，如果用户输入一个日期然后将其删除，则TextBox中的DatePicker会进行某种验证，我想禁用该日期。另外，如果我在“验证”之后保存值，那么之前输入的日期就是保存的日期。

如果没有任何文本，我试图将日期设置为null，但这是行不通的。

private void PART_TextBoxFim_TextChanged(object sender, TextChangedEventArgs e)
{
    if (Dp_DataFim.Text == null)
    {
        Dp_DataFim.SelectedDate = null;
        Dp_DataFim.DisplayDate = DateTime.Today;
    }
}

在页面类中，我有这个：

public Nullable<DateTime> Prop { get; set; }

datepicker的XAML是这样的：

<DatePicker x:Name="Dp_DataFim" Grid.Row="0" Grid.Column="2" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="10,250,0,0" FontSize="16" Height="20" Width="230" SelectedDate="{Binding Prop}" IsTodayHighlighted="False" SelectedDateFormat="Short" BorderThickness="0" Padding="0" BorderBrush="{x:Null}" IsTabStop="True" SelectedDateChanged="Dp_DataFim_SelectedDateChanged" Visibility="Hidden">
    <DatePicker.Resources>
        <Style TargetType="{x:Type DatePickerTextBox}">
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate>
                        <TextBox x:Name="PART_TextBox" Text="{Binding Path=SelectedDate, RelativeSource={RelativeSource AncestorType={x:Type DatePicker}}, StringFormat='dd/MM/yyyy HH:mm:ss'}" Background="#FF494949" Foreground="#FFEEEEEE" BorderThickness="0" IsReadOnly="False" TextChanged="PART_TextBoxFim_TextChanged"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </DatePicker.Resources>
</DatePicker>

我注意到这种情况发生时，出现了这样的错误：

System.Windows.Data Error: 7 : ConvertBack cannot convert value '' (type 'String'). BindingExpression:Path=SelectedDate; DataItem='DatePicker' (Name='Dp_DataFim'); target element is 'TextBox' (Name='PART_TextBox'); target property is 'Text' (type 'String') FormatException:'System.FormatException: The string was not recognized as a valid DateTime value.
   em System.DateTimeParse.Parse(String s, DateTimeFormatInfo dtfi, DateTimeStyles styles)
   em System.Convert.ToDateTime(String value, IFormatProvider provider)
   em System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
   em System.Windows.Data.BindingExpression.ConvertBackHelper(IValueConverter converter, Object value, Type sourceType, Object parameter, CultureInfo culture)'

Answer 1

将SelectedDate的{{1}}属性绑定到DatePicker源属性。

如果通过为Nullable<DateTime>创建自定义ControlTemplate并将其DatePickerTextBox属性绑定到Text属性的方式来更改日期格式，则可以使用一个简单的转换器类，将空的SelectedDate转换为string：

default(DateTime?)

用法：

public class StringToDateTimeConverter : IValueConverter
{
    private const string DateFormat = "dd/MM/yyyy HH:mm:ss";

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        DateTime? dt = (DateTime?)value;
        return dt.HasValue ? dt.Value.ToString(DateFormat, CultureInfo.InvariantCulture) : string.Empty;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        string s = value.ToString();
        if (string.IsNullOrEmpty(s))
            return default(DateTime?);

        DateTime dt;
        return DateTime.TryParseExact(s, DateFormat, CultureInfo.InvariantCulture, DateTimeStyles.None, out dt) ? dt : default(DateTime?);
    }
}

禁用datepicker文本框转换/验证失去焦点

1 个答案: