可空数据库属性，但texbox仍然显示内容时删除红色边框 [英] Nullable database property but texbox still shows red border when content deleted

问题描述

你好我绑定一个WPF文本框的实体框架特性如下：

Hi I am binding a WPF textbox to an Entity Framework property as follows:

<TextBox Grid.Column="1" Grid.Row="0" Margin="5,2" 
         Text="{Binding Path=MyEntityObject.SizeLower, Mode=TwoWay}" />

它结合精致的财产，当我改变它，因为预计其保存到数据库中。但是，如果我删除文本框的内容，我得到的红色错误边框周围。我没有在任何地方验证，所以我猜texbox抱怨不是可为空值。但实际上这个属性在DB是空的，因此我不明白为什么它会报错。

It binds fine to the property and when I change it, it saves to the DB as expected. But if I delete the content of the Textbox I get the red error border around it. I dont have any validator in place so I am guessing the texbox is complaining about the value not being nullable. But in fact this property in the DB is nullable, so I cannot understand why it would error.

本系统生成EF属性定义如下：

The system generated EF property definition is as follows:

<EdmScalarPropertyAttribute(EntityKeyProperty:=false, IsNullable:=true)>
<DataMemberAttribute()>
Public Property SizeLower() As Nullable(Of Global.System.Int64)
    Get
        Return _SizeLower
    End Get
    Set
        OnSizeLowerChanging(value)
        ReportPropertyChanging("SizeLower")
        _SizeLower = StructuralObject.SetValidValue(value)
        ReportPropertyChanged("SizeLower")
        OnSizeLowerChanged()
    End Set
End Property

Private _SizeLower As Nullable(Of Global.System.Int64)

有我丢失的东西？我想绑定系统能够确定是否财产是可为空，并允许空值如果是这样？

Is there something I am missing? I thought the binding system was able to determine if a property was nullable and allow nulls if so?

我怎么能看到的错误是什么？悬停似乎没有这样的伎俩。

How can I see what the error is? Hovering doesnt seem to do the trick.

感谢您的任何建议。

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其他信息

=================================== ADDITIONAL INFO

如果我选择全部删除，然后更改焦点，会出现验证框。之前和之后这里有一个抓屏。我也已经证实，我可以手动把空值在数据库中的绑定属性所以那不是问题。

If I select all and delete, then change focus, the validation box appears. Here's a screencapture before and after. Also I have confirmed that I can manually put NULLs in the database for the bound properties so thats not the problem.

拒绝。试图把这里的图片，但我没有10分...！
下面是一个异地而不是链接：点击此处

DENIED. Tried to put picture here but I dont have 10 points...! Here is an offsite link instead: CLICK HERE

推荐答案

您应该在 TargetNullValue 属性添加到您的绑定：

You should add the TargetNullValue property to your binding:

<TextBox Grid.Column="1" Grid.Row="0" Margin="5,2" 
         Text="{Binding Path=MyEntityObject.SizeLower, 
         Mode=TwoWay, 
         TargetNullValue=''}" />

这告诉绑定设置时，对待 MyEntityObject.SizeLower 空值的String.Empty用于显示，作为的String.Empty空。

This tells the binding to treat null values in MyEntityObject.SizeLower as string.empty for display, and string.empty as null when setting.

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