Question

所以我写了以下DP和ValidationRule：

public class ComparisonValue : DependencyObject
{
    public Object ComparisonObject
    {
        get { return (Object)GetValue(ComparisonObjectProp); }
        set { 
            SetValue(ComparisonObjectProp, value); 
        }
    }
    public static readonly DependencyProperty ComparisonObjectProp =
        DependencyProperty.Register("ComparisonObject", typeof(object), typeof(ComparisonValue), new UIPropertyMetadata(null));
}

public class ObjectComparisonValidator : ValidationRule
{
    private ComparisonValue _ObjectToCompare;
    public ComparisonValue ObjectToCompare
    {
        get
        {
            return _ObjectToCompare;
        }
        set
        {
            _ObjectToCompare = value;
        }

    }

    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        if (value != null)
        {
            if (!value.Equals(ObjectToCompare.ComparisonObject))
            {
                return new ValidationResult(false, "Values are not equal");
            }
            else
            {
                return new ValidationResult(true, null);
            }
        }
        else
        {
            if (value != ObjectToCompare.ComparisonObject)
            {
                return new ValidationResult(false, "Values are not equal");
            }
            else
            {
                return new ValidationResult(true, null);
            }
        }
    }
}

然后在我的XAML中，我有以下标记：

<UserControl.Resources>
    <l:EnumToStringConverter x:Key="CustomEnumConverter"/>
    <l:BooleanToBrushConverter x:Key="BooleanToBrushConverter"/>
    <l:ObjectComparisonValidator x:Key="ObjectComparisonValidator"/>
    <l:ComparisonValue x:Key="ComparisonValue"/>
</UserControl.Resources>

....

            <TextBox Grid.Row="2" Grid.Column="1" Grid.ColumnSpan="2" Height="25" Text="{Binding Path=NetworkKey.Value, UpdateSourceTrigger=PropertyChanged}">
                <TextBox.Background>
                    <Binding Path="NetworkKey.Changed" Converter="{StaticResource BooleanToBrushConverter}">
                        <Binding.ConverterParameter>
                            <x:Array Type="Brush">
                                <SolidColorBrush Color="Yellow"/>
                                <SolidColorBrush Color="White"/>
                            </x:Array>
                        </Binding.ConverterParameter>
                    </Binding>
                </TextBox.Background>
            </TextBox>

....

            <TextBox Grid.Row="3" Grid.Column="1" Grid.ColumnSpan="2" Height="25">                    
                <TextBox.Text>
                    <Binding Path="DuplicateNetworkKey.Value" UpdateSourceTrigger="PropertyChanged">
                        <Binding.ValidationRules>
                            <l:ObjectComparisonValidator>
                                <l:ObjectComparisonValidator.ObjectToCompare>
                                    <l:ComparisonValue ComparisonObject="{Binding Path=NetworkKey.Value}"/>
                                </l:ObjectComparisonValidator.ObjectToCompare>
                            </l:ObjectComparisonValidator>
                        </Binding.ValidationRules>
                    </Binding>
                </TextBox.Text>
                <TextBox.Background>
                    <Binding Path="DuplicateNetworkKey.Changed" Converter="{StaticResource BooleanToBrushConverter}">
                        <Binding.ConverterParameter>
                            <x:Array Type="Brush">
                                <SolidColorBrush Color="Yellow"/>
                                <SolidColorBrush Color="White"/>
                            </x:Array>
                        </Binding.ConverterParameter>
                    </Binding>
                </TextBox.Background>
            </TextBox>

现在我遇到的问题是调用Validation规则的Validate方法，但是当触发NetworkKey的绑定时，对象的ComparisonValue中的Setter永远不会被调用，所以只要验证规则运行， ObjectComparisonValidator.ObjectToCompare的ComparisonObject属性为null，因此验证失败。我对ComparisonObject的绑定有什么问题？

只是为了澄清一点，NetworkKey和DuplicateKey（VM中的props）的类型是INPC类。继承了他们的代码：

public class ValueField<T> : AChangeReportingViewModel, INotifyPropertyChanged
{
    private T _OriginalVal;
    public T OriginalVal
    {
        get
        {
            return _OriginalVal;
        }
        set
        {
            _OriginalVal = value;
            Value = value;
            Changed = false;
            PropertyChanged(this, new PropertyChangedEventArgs("OriginalVal"));
        }
    }
    private T _Value;
    public T Value
    {
        get
        {
            return _Value;
        }
        set
        {
            _Value = value;
            if (_Value == null)
            {
                if (_OriginalVal != null) Changed = true;
            }
            else
            {
                Changed = !_Value.Equals(_OriginalVal);
            }
            PropertyChanged(this, new PropertyChangedEventArgs("Value"));
        }
    }
    private Boolean _Changed;
    public Boolean Changed
    {
        get
        {
            return _Changed;
        }
        set
        {
            if (_Changed != value)
            {
                if (value) ChangeMade();
                else ChangeReversed();
            }
            _Changed = value;
            PropertyChanged(this, new PropertyChangedEventArgs("Changed"));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged = delegate { };
}

Answer 1

<Binding Path="DuplicateNetworkKey.Value" UpdateSourceTrigger="PropertyChanged">
                    <Binding.ValidationRules>
                        <l:ObjectComparisonValidator>
                            <l:ObjectComparisonValidator.ObjectToCompare>
                                <l:ComparisonValue ComparisonObject="{Binding Path=NetworkKey.Value}"/>
                            </l:ObjectComparisonValidator.ObjectToCompare>
                        </l:ObjectComparisonValidator>
                    </Binding.ValidationRules>
                </Binding>

内部绑定对象不是可视树的一部分，因此不会继承父级的数据上下文。要绑定在可视树之外，请使用x:Reference绑定：

<l:ComparisonValue ComparisonObject="{Binding Source={x:Reference Root} 
                                      Path=DataContext.NetworkKey.Value}"/>

它与ElementName绑定类似，但您无法在可视树之外执行这些绑定。请注意，此示例中的“Root”是根UI元素的名称。

使用依赖项属性参数化ValidationRules的麻烦

1 个答案: