c# - WPF 绑定(bind)到 ElementName 引发 NullReferenceException

Question

我正在尝试验证 WPF 中的一些输入数据，并且正在使用此处所述的 DataResource 代理: http://www.wpfmentor.com/2009/01/how-to-add-binding-to-property-on.html

所以，这是我的 XAML(简化版):

<mvvm:BaseDataView
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:md="clr-namespace:Mfc.Mvvm.Master"
    >
<mvvm:BaseDataView.Resources>
    <ResourceDictionary>
        <md:DataResource x:Key="mmSS" BindingTarget="{Binding ElementName=tbMmss,Path=Text}"/>
        <md:DataResource x:Key="mmTS" BindingTarget="{Binding ElementName=tbMmts,Path=Text}"/>
    </ResourceDictionary>
</mvvm:BaseDataView.Resources>
...
<TextBox x:Name="tbMmts" HorizontalAlignment="Left" VerticalAlignment="Top" Grid.Row="2" Grid.Column="1" Width="100" Margin="3,3,0,0">
            <TextBox.Text>
                <Binding Path="MTS" UpdateSourceTrigger="PropertyChanged">
                    <Binding.ValidationRules>
                        <md:DoubleRangeValidationRule MinValue="10.0" MaxValue="5000.0"/>
                        <md:LessThanValidationRule>
                            <md:LessThanValidationRule.LessThanChecker>
                                <md:ProxyForComparisonString
                                    CompareTo="{md:DataResourceBinding DataResource={StaticResource mmSS}}">
                                </md:ProxyForComparisonString>
                            </md:LessThanValidationRule.LessThanChecker>
                        </md:LessThanValidationRule>
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>
...

<TextBox x:Name="tbMmss" HorizontalAlignment="Left" VerticalAlignment="Top" Grid.Row="3" Grid.Column="1" Width="100" Margin="3,3,0,0">
            <TextBox.Text>
                <Binding Path="STS" UpdateSourceTrigger="PropertyChanged">
                    <Binding.ValidationRules>
                        <md:DoubleRangeValidationRule MinValue="10.0" MaxValue="5000.0"/>
                        <md:GreaterThanValidationRule>
                            <md:GreaterThanValidationRule.GreaterThanChecker>
                                <md:ProxyForComparisonString
                                    CompareTo="{md:DataResourceBinding DataResource={StaticResource mmTS}}">
                                </md:ProxyForComparisonString>
                            </md:GreaterThanValidationRule.GreaterThanChecker>
                        </md:GreaterThanValidationRule>
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>

第二个 文本框的验证工作完美，但它因第一个 文本框的 NullReferenceException 而崩溃。 DataResource 似乎没有得到初始化，调试说

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=tbMmss'. BindingExpression:Path=Text; DataItem=null; target element is 'DataResource'

有什么想法吗？谢谢!

Answer 1

您对此采取了完全错误的方法。不要使用 Freezable。他们很坏。他们不会被困在资源中并像桥梁一样被侵犯!请使用附加属性或 INotifyDataError 信息来干净且正确地解决此问题。