blocks|key|1168453|text|您可以尝试使用ValueConverter+(IValueConverter)+http://msdn.microsoft.com/en-us/library/system.windows.data.ivalueconverter.aspx|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1168454|我的后脑勺，就像这样：|1168455|public+class+DoubleConverter+:+IValueConverter
{
++++public+object+Convert(object+value,+Type+targetType,+
++++++++object+parameter,+CultureInfo+culture)
++++{
++++++++return+(double)value;
++++}

++++public+object+ConvertBack(object+value,+Type+targetType,+
++++++++object+parameter,+CultureInfo+culture)
++++{
++++var+doubleValue+=+Convert.ToDouble(value);

++++return+(doubleValue+==+0+?+null+:+doubleValue);
++++}
}|code-block|syntax|javascript|1168456|(可能需要一些调整)|1168457|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.windows.data.ivalueconverter.aspx^0|14|28|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|Z|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|C|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

You can try using a ValueConverter (IValueConverter)
<a href="http://msdn.microsoft.com/en-us/library/system.windows.data.ivalueconverter.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/system.windows.data.ivalueconverter.aspx</a>

Of the back of my head here, something like:

<pre><code>public class DoubleConverter : IValueConverter
{
 public object Convert(object value, Type targetType, 
 object parameter, CultureInfo culture)
 {
 return (double)value;
 }

 public object ConvertBack(object value, Type targetType, 
 object parameter, CultureInfo culture)
 {
 var doubleValue = Convert.ToDouble(value);

 return (doubleValue == 0 ? null : doubleValue);
 }
}
</code></pre>

(Might need some tweaking though)

blocks|key|1168500|text|这个值转换器应该可以做到这一点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1168501|public+class+StringToNullableDecimalConverter+:+IValueConverter
{
++++public+object+Convert(object+value,+Type+targetType,+object+parameter,+
++++++++CultureInfo+culture)
++++{
++++++++decimal?+d+=+(decimal?)value;
++++++++if+(d.HasValue)
++++++++++++return+d.Value.ToString(culture);
++++++++else
++++++++++++return+String.Empty;
++++}

++++public+object+ConvertBack(object+value,+Type+targetType,+
++++++++object+parameter,+CultureInfo+culture)
++++{
++++++++string+s+=+(string)value;
++++++++if+(String.IsNullOrEmpty(s))
++++++++++++return+null;
++++++++else
++++++++++++return+(decimal?)decimal.Parse(s,+culture);
++++}
}|code-block|syntax|javascript|1168502|在资源中声明此转换器的实例：|1168503|<Window.Resources>
++++<local:StringToNullableDecimalConverter+x:Key="nullDecimalConv"/>
</Window.Resources>|1168504|并在绑定中使用它：|1168505|<TextBox+Text="{Binding+Price,+Converter={StaticResource+nullDecimalConv}}"/>|1168506|请注意，TargetNullValue在这里并不合适:它用于定义当绑定的source为null时应该使用哪个值。这里Price不是源，它是源的属性...|offset|length|style|CODE|1168507|entityMap^0|0|0|0|0|0|0|4|F|10|6|1M|5|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|12|8|@$Q|13|R|14|S|T]|$Q|15|R|16|S|T]|$Q|17|R|18|S|T]]|9|@]|A|$]]|$1|U|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|V|$]]

This value converter should do the trick :

<pre><code>public class StringToNullableDecimalConverter : IValueConverter
{
 public object Convert(object value, Type targetType, object parameter, 
 CultureInfo culture)
 {
 decimal? d = (decimal?)value;
 if (d.HasValue)
 return d.Value.ToString(culture);
 else
 return String.Empty;
 }

 public object ConvertBack(object value, Type targetType, 
 object parameter, CultureInfo culture)
 {
 string s = (string)value;
 if (String.IsNullOrEmpty(s))
 return null;
 else
 return (decimal?)decimal.Parse(s, culture);
 }
}
</code></pre>

Declare an instance of this converter in the ressources :

<pre><code>&lt;Window.Resources&gt;
 &lt;local:StringToNullableDecimalConverter x:Key="nullDecimalConv"/&gt;
&lt;/Window.Resources&gt;
</code></pre>

And use it in your binding :

<pre><code>&lt;TextBox Text="{Binding Price, Converter={StaticResource nullDecimalConv}}"/&gt;
</code></pre>

Note that <code>TargetNullValue</code> is not appropriate here : it is used to define which value should be used when the <code>source</code> of the binding is null. Here <code>Price</code> is not the source, it's a property of the source...

blocks|key|1383623|text|我使用的是.NET+3.5+SP1，所以非常简单：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1383624|<TextBox+Text="{Binding+Price,+TargetNullValue=''}"/>|code-block|syntax|javascript|1383625|它代表(感谢Gregor的评论)：|1383626|<TextBox+Text="{Binding+Price,+TargetNullValue={x:Static+sys:String.Empty}}"/>|1383627|sys是为mscorlib中的System导入的xml命名空间|offset|length|style|CODE|1383628|xmlns:sys="clr-namespace:System;assembly=mscorlib"|1383629|希望这能帮上忙。|1383630|entityMap^0|0|0|0|0|0|3|5|8|F|6|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|10|8|@$M|11|N|12|O|P]|$M|13|N|14|O|P]|$M|15|N|16|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|18|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|V|$]]

I am using .NET 3.5 SP1 so it's very simple:

<pre><code>&lt;TextBox Text="{Binding Price, TargetNullValue=''}"/&gt;
</code></pre>

Which stands for (thanks Gregor for your comment):

<pre><code>&lt;TextBox Text="{Binding Price, TargetNullValue={x:Static sys:String.Empty}}"/&gt;
</code></pre>

<code>sys</code> is the imported xml namespace for <code>System</code> in <code>mscorlib</code>:

<pre><code>xmlns:sys="clr-namespace:System;assembly=mscorlib"
</code></pre>

Hope that helped.

please take a look at the following line

<pre><code>&lt;TextBox Text="{Binding Price}"/&gt;
</code></pre>

This Price property from above is a <code>Decimal?</code> (Nullable decimal).

I want that if user deletes the content of the textbox (i.e. enters empty string, it should automatcally update source with null (Nothing in VB).

Any ideas on how I can do it 'Xamly'?

Set value to null in WPF binding

请看下面这行<TextBox Text="{Binding Price}"/>上面的Price属性是一个Decimal? (可以为空的小数)。我希望如果用户删除了文本框的内容(即输入空字符串)，它应该自动更新为null的源代码(在VB中为Nothing)。我该怎么做'Xamly‘，有什么建议吗？

问在WPF绑定中将值设置为null
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