在 WPF 应用程序中绑定可为空的日期时间
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/28561190/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Binding a nullable datetime within WPF application
提问by Lamloumi Afif
I have a wpf application in which I had this property to bind to a datepicker
我有一个 wpf 应用程序，在其中我将此属性绑定到日期选择器
public Nullable<System.DateTime> dpc_date_engagement { get; set; }
So I add a converter :
所以我添加了一个转换器：
public class DateConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value != null)
return ((DateTime)value).ToShortDateString();
return String.Empty;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
string strValue = value.ToString();
DateTime resultDateTime;
return DateTime.TryParse(strValue, out resultDateTime) ? resultDateTime : value;
}
}
In XAML file :
在 XAML 文件中：
<DatePicker >
<DatePicker.Text>
<Binding Path="dpc_date_engagement" UpdateSourceTrigger="PropertyChanged">
<Binding.Converter>
<converter:DateConverter/>
</Binding.Converter>
</Binding>
</DatePicker.Text>
</DatePicker>
The problem is when the date is null, the displayed text is 1/1/0001.
问题是当日期为空时，显示的文本是 1/1/0001。
- How can I fix my code to display an empty string instead of 01/01/0001, for null values?
- 对于空值，如何修复我的代码以显示空字符串而不是 01/01/0001？
回答by Clemens
The Nullable valuepassed to your converter is not itself null, even if it holds a nullvalue (it can't even be null, because it is a struct and therefore not nullable).
value传递给转换器的 Nullable不是它自己null，即使它持有一个null值（它甚至不能为空，因为它是一个结构体，因此不可为空）。
So instead of comparing valueto null, you'll have to cast it to Nullable<Datetime>and then check its HasValueproperty.
因此，而不是比较value来null，你就必须将它转换为Nullable<Datetime>，然后检查其HasValue属性。
Moreover, you seem to have something like DateTime.MinValuein your bound property instead of null. So you should check against that, too:
此外，您DateTime.MinValue的绑定属性中似乎有类似的东西，而不是null. 所以你也应该检查一下：
public object Convert(...)
{
var nullable = (Nullable<DateTime>)value;
if (nullable.HasValue && nullable.Value > DateTime.MinValue)
{
return nullable.Value.ToShortDateString();
}
return String.Empty;
}
回答by Jorge Villalobos Carvajal
The easiest way I've been found to handle nullableDateTimefield using in a DatePickeris setting TargetNullValue=''
我发现在DatePicker 中使用处理可为空的DateTime字段的最简单方法是设置TargetNullValue=''
In XAML file:
在 XAML 文件中：
<DatePicker Text={Binding dpc_date_engagement, Mode=TwoWay, TargetNullValue='', UpdateSourceTrigger=PropertyChanged} />
