.net - WPF验证装饰器-仅显示控件之前是否已保持焦点

在我的WPF应用程序中，我只想在用户编辑/输入/关注控件后才显示验证装饰器。这样，用户就有机会在字段中提供有效的输入，并且只有当他们选择不输入时，才会显示验证。

我们希望鼓励每个字段都填写完整，以便在表单第一次打开时指出必填字段，这样一来，用户将立即倾向于完成所需的内容，以消除可能也可以避免的大红色验证错误。表单的流程。

是否有办法知道控件是否已成为焦点？ 附加属性可能有用吗？

如果它有助于提供更具体的响应:这是我当前的验证样式，该样式显示红色边框(如果控件具有边框)和带有感叹号的小惊叹号，并带有错误消息的提示(实际上是非常标准的):

<Style TargetType="Control">
    <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="true">
            <Setter Property="ToolTip"
                    Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                    Path=(Validation.Errors).CurrentItem.ErrorContent}"/>

            <Setter Property="Validation.ErrorTemplate">
                <Setter.Value>
                    <ControlTemplate>
                        <DockPanel LastChildFill="true">
                            <Image Source="../Resources/Icons/Error.ico" Margin="4" Width="15" ToolTip="{Binding ElementName=customAdorner, Path=AdornedElement.(Validation.Errors).CurrentItem.ErrorContent}" />
                            <AdornedElementPlaceholder Name="customAdorner" VerticalAlignment="Center" >
                                <Border BorderBrush="red" BorderThickness="1" Visibility="{Binding ElementName=customAdorner, Path=AdornedElement.BorderThickness, Converter={StaticResource hasBorderToVisibilityConverter}}" />
                            </AdornedElementPlaceholder>
                        </DockPanel>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Trigger>
        <Trigger Property="IsVisible" Value="False">
            <Setter Property="Validation.ErrorTemplate" Value="{x:Null}"/>
        </Trigger>
    </Style.Triggers>
</Style>

最佳答案

您可以将“附加行为”与“附加属性”结合使用。附加行为ObserveFocus将订阅GotFocus事件，并在事件处理程序中将HasHeldFocus附加属性设置为True
它可以像这样在ViewModel中设置属性

<Button local:HasHeldFocusBehavior.ObserveFocus="True"
        local:HasHeldFocusBehavior.HasHeldFocus="{Binding HasHeldFocus,
                                                          Mode=OneWayToSource}"/>

这是一个示例，说明如何在聚焦后将其用于更改Background的Button

<Style TargetType="Button">
    <Setter Property="Background" Value="Red"/>
    <Setter Property="local:HasHeldFocusBehavior.ObserveFocus" Value="True"/>
    <Style.Triggers>
        <DataTrigger Binding="{Binding RelativeSource={RelativeSource Self},
                                       Path=(local:HasHeldFocusBehavior.HasHeldFocus)}"
                        Value="True">
            <Setter Property="Background" Value="Green"/>
        </DataTrigger>
    </Style.Triggers>
</Style>

HasHeldFocus行为

public static class HasHeldFocusBehavior
{
    public static readonly DependencyProperty ObserveFocusProperty =
        DependencyProperty.RegisterAttached("ObserveFocus",
                                            typeof(bool),
                                            typeof(HasHeldFocusBehavior),
                                            new UIPropertyMetadata(false, OnObserveFocusChanged));
    public static bool GetObserveFocus(DependencyObject obj)
    {
        return (bool)obj.GetValue(ObserveFocusProperty);
    }
    public static void SetObserveFocus(DependencyObject obj, bool value)
    {
        obj.SetValue(ObserveFocusProperty, value);
    }
    private static void OnObserveFocusChanged(DependencyObject dpo,
                                              DependencyPropertyChangedEventArgs e)
    {
        UIElement element = dpo as UIElement;
        element.Focus();
        if ((bool)e.NewValue == true)
        {
            SetHasHeldFocus(element, element.IsFocused);
            element.GotFocus += element_GotFocus;
        }
        else
        {
            element.GotFocus -= element_GotFocus;
        }
    }
    static void element_GotFocus(object sender, RoutedEventArgs e)
    {
        UIElement element = sender as UIElement;
        SetHasHeldFocus(element, true);
    }

    private static readonly DependencyProperty HasHeldFocusProperty =
        DependencyProperty.RegisterAttached("HasHeldFocus",
                                            typeof(bool),
                                            typeof(HasHeldFocusBehavior),
                                            new UIPropertyMetadata(false));
    public static void SetHasHeldFocus(DependencyObject element, bool value)
    {
        element.SetValue(HasHeldFocusProperty, value);
    }
    public static bool GetHasHeldFocus(DependencyObject element)
    {
        return (bool)element.GetValue(HasHeldFocusProperty);
    }
}

更新

您可以使用MultiTrigger替换Validation.HasError触发器

<Style TargetType="Control">
    <Style.Triggers>
        <MultiDataTrigger>
            <MultiDataTrigger.Conditions>
                <Condition Binding="{Binding RelativeSource={RelativeSource Self},
                                             Path=(Validation.HasError)}"
                           Value="True"/>
                <Condition Binding="{Binding RelativeSource={RelativeSource Self},
                                             Path=(local:HasHeldFocusBehavior.HasHeldFocus)}"
                           Value="True"/>
            </MultiDataTrigger.Conditions>
            <!-- Setters.. -->
        </MultiDataTrigger>
        <!-- ... -->
    </Style.Triggers>
</Style>