从UserControl访问Validation.HasError

Question

could someone help me, how can I access the HasError property from my custom usercontrol?

<UserControl.Resources>
    <Style TargetType="{x:Type TextBox}">
        <Setter Property="Margin" Value="0,2,0,2" />
        <Setter Property="Validation.ErrorTemplate">
            <Setter.Value>
                <ControlTemplate>
                    <DockPanel LastChildFill="true">
                        <Border Background="Red" DockPanel.Dock="right" Margin="5,0,0,0" Width="20" Height="20" CornerRadius="10"
                                ToolTip="{Binding ElementName=customAdorner, Path=AdornedElement.(Validation.Errors)[0].ErrorContent}">
                            <!--<TextBlock Text="!" VerticalAlignment="center" HorizontalAlignment="center" FontWeight="Bold" Foreground="white">
                            </TextBlock>-->
                        </Border>
                        <AdornedElementPlaceholder Name="customAdorner" VerticalAlignment="Center" >
                            <Border BorderBrush="red" BorderThickness="1" />
                        </AdornedElementPlaceholder>
                    </DockPanel>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</UserControl.Resources>

<Grid x:Name="Layout" DataContext="{Binding RelativeSource={RelativeSource AncestorType=UserControl}}">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="Auto" />
    </Grid.ColumnDefinitions>
    <TextBox Name="TbHostname" Grid.Column="1"
             VerticalContentAlignment="Center" MinWidth="200">
        <TextBox.Text>
            <Binding Path="Hostname" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" ValidatesOnDataErrors="True" NotifyOnValidationError="True">
                <Binding.ValidationRules>
                    <serverStarter2:HostnameValidator ErrorMessage="Wrong hostname format."/>
                </Binding.ValidationRules>
            </Binding>
        </TextBox.Text>
    </TextBox>
</Grid>

This is my custom usercontrol, that is used in MainWindow.xaml . What I want, when everything is fine, enable submit button, when not, disable it.

Here is code for button inside MainWindow.xaml :

<Button Content="Test connection" Command="{Binding ConnectionViewModel.TestConnectionCommand}"
                          >
                        <Button.Style>
                            <Style TargetType="{x:Type Button}" >
                                <Style.Triggers>
                                    <DataTrigger Binding="{Binding Path=(Validation.HasError), ElementName=StudioHostname}" Value="True">
                                        <Setter Property="IsEnabled" Value="False"/>
                                    </DataTrigger>
                                </Style.Triggers>
                            </Style>
                        </Button.Style>
                    </Button>

ElementName=StudioHostname is name of my UserControl.

Answer 1

It is the Validation.HasError attached property of the TextBox in the UserControl that is being set to true . The Validation.HasError property of the UserControl itself won't be set and you can't bind to an element that is defined the UserControl from the MainWindow using an ElementName .

You are doing this wrong. What you should do is to implement the validation in the view model class where the Hostname property is defined. You can do this by implementing the INotifyDataErrorInfo interface.

Then you can simply bind the IsEnabled property of the Button to the HasErrors property of the view model, or bind it to an ICommand whose CanExecute method returns the value of the HasErrors property.

There is an example of how to implement the interface available here: https://social.technet.microsoft.com/wiki/contents/articles/19490.wpf-4-5-validating-data-in-using-the-inotifydataerrorinfo-interface.aspx .