In a WPF application I am using a template to style the validation tooltip (red tooltip with rounded edges):

<ControlTemplate x:Key="CommonValidationToolTipTemplate" TargetType="ToolTip">
    <Grid x:Name="Root" Margin="5,0" RenderTransformOrigin="0,0" Opacity="0">
        <VisualStateManager.VisualStateGroups>
            <VisualStateGroup Name="OpenStates">
                <VisualStateGroup.Transitions>
                    <VisualTransition GeneratedDuration="0" />
                    <VisualTransition To="Open" GeneratedDuration="0:0:0">
                        <Storyboard>
                            <DoubleAnimation Storyboard.TargetName="Root" Storyboard.TargetProperty="Opacity" To="1" Duration="0:0:0" />
                        </Storyboard>
                    </VisualTransition>
                </VisualStateGroup.Transitions>
                <VisualState x:Name="Closed">
                    <Storyboard>
                        <DoubleAnimation Storyboard.TargetName="Root" Storyboard.TargetProperty="Opacity" To="0" Duration="0" />
                    </Storyboard>
                </VisualState>
                <VisualState x:Name="Open">
                    <Storyboard>
                        <DoubleAnimation Storyboard.TargetName="Root" Storyboard.TargetProperty="Opacity" To="1" Duration="0" />
                    </Storyboard>
                </VisualState>
            </VisualStateGroup>
        </VisualStateManager.VisualStateGroups>

        <Border Margin="4,4,-4,-4" Background="#052A2E31" CornerRadius="5" />
        <Border Margin="3,3,-3,-3" Background="#152A2E31" CornerRadius="4" />
        <Border Margin="2,2,-2,-2" Background="#252A2E31" CornerRadius="3" />
        <Border Margin="1,1,-1,-1" Background="#352A2E31" CornerRadius="2" />

        <Border Background="#FFDC000C" CornerRadius="2">
            <TextBlock Foreground="White" Margin="8,4,8,4" MaxWidth="250" TextWrapping="Wrap" Text="{Binding (Validation.Errors)[0].ErrorContent}" />
        </Border>
    </Grid>
</ControlTemplate>

The template is applied to the view elements by using a style:

<Style x:Key="ValidatingControlStyle" TargetType="{x:Type FrameworkElement}">
        <Setter Property="Validation.ErrorTemplate" Value="{StaticResource CommonValidationToolTipTemplate}" />
        <Style.Triggers>
            <Trigger Property="Validation.HasError" Value="True">
                <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}" />
            </Trigger>
        </Style.Triggers>
</Style>

Unfortunately the custom tooltip does not show up on validation errors. The "standard" tooltip is displayed.

What am I doing wrong?

CodePudding user response：

Why are you setting Validation.ErrorTemplate to a ToolTip style...?

You should set the Template property of the ToolTip in your Style:

<Style x:Key="ValidatingControlStyle" TargetType="{x:Type FrameworkElement}">
    <Style.Resources>
        <Style TargetType="ToolTip">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="ToolTip">
                        <Grid x:Name="Root" Margin="5,0" RenderTransformOrigin="0,0" Opacity="0">
                            <VisualStateManager.VisualStateGroups>
                                <VisualStateGroup Name="OpenStates">
                                    <VisualStateGroup.Transitions>
                                        <VisualTransition GeneratedDuration="0" />
                                        <VisualTransition To="Open" GeneratedDuration="0:0:0">
                                            <Storyboard>
                                                <DoubleAnimation Storyboard.TargetName="Root" Storyboard.TargetProperty="Opacity" To="1" Duration="0:0:0" />
                                            </Storyboard>
                                        </VisualTransition>
                                    </VisualStateGroup.Transitions>
                                    <VisualState x:Name="Closed">
                                        <Storyboard>
                                            <DoubleAnimation Storyboard.TargetName="Root" Storyboard.TargetProperty="Opacity" To="0" Duration="0" />
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="Open">
                                        <Storyboard>
                                            <DoubleAnimation Storyboard.TargetName="Root" Storyboard.TargetProperty="Opacity" To="1" Duration="0" />
                                        </Storyboard>
                                    </VisualState>
                                </VisualStateGroup>
                            </VisualStateManager.VisualStateGroups>

                            <Border Margin="4,4,-4,-4" Background="#052A2E31" CornerRadius="5" />
                            <Border Margin="3,3,-3,-3" Background="#152A2E31" CornerRadius="4" />
                            <Border Margin="2,2,-2,-2" Background="#252A2E31" CornerRadius="3" />
                            <Border Margin="1,1,-1,-1" Background="#352A2E31" CornerRadius="2" />

                            <Border Background="#FFDC000C" CornerRadius="2">
                                <TextBlock Foreground="White" Margin="8,4,8,4" MaxWidth="250" TextWrapping="Wrap" 
                                                   Text="{TemplateBinding Content}" />
                            </Border>
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Style.Resources>
    <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="True">
            <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, 
                        Path=(Validation.Errors)[0].ErrorContent}" />
        </Trigger>
    </Style.Triggers>
</Style>

...which you then apply to an element, for example like this:

<TextBox Text="{Binding Text}" Style="{StaticResource ValidatingControlStyle}" />