Vfrdtyky

I am using a typical Style to display validation errors as a tooltip from IErrorDataInfo for a textbox as shown below and it works fine.

    <Style TargetType="{x:Type TextBox}">

        <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>

But when i try to do the same thing for a ComboBox like this it fails

    <Style TargetType="{x:Type ComboBox}">

        <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>

The error I get in the output window is:

System.Windows.Data Error: 17 : Cannot get 'Item' value (type 'ValidationError') from '(Validation.Errors)' (type 'ReadOnlyObservableCollection`1'). BindingExpression:Path=(0)[0].ErrorContent; DataItem='ComboBox' (Name='ownerComboBox'); target element is 'ComboBox' (Name='ownerComboBox'); target property is 'ToolTip' (type 'Object') ArgumentOutOfRangeException:'System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.Parameter name: index'

Oddly it also attempts to make invalid Database changes when I close the window if I change any ComboBox values (This is also when the binding error occurs)!!!

Cannot insert the value NULL into column 'EmpFirstName', table 'OITaskManager.dbo.Employees'; column does not allow nulls. INSERT fails.
The statement has been terminated.

Simply by commenting the style out everyting works perfectly. How do I fix this?

Just in case anyone needs it one of the comboBox' xaml follows:

<ComboBox ItemsSource="{Binding Path=Employees}" 

                  SelectedValuePath="EmpID"                       

                  SelectedValue="{Binding Path=SelectedIssue.Employee2.EmpID,

                     Mode=OneWay, ValidatesOnDataErrors=True}" 

                  ItemTemplate="{StaticResource LastNameFirstComboBoxTemplate}"

                  Height="28" Name="ownerComboBox" Width="120" Margin="2" 

                  SelectionChanged="ownerComboBox_SelectionChanged" />





<DataTemplate x:Key="LastNameFirstComboBoxTemplate">

    <TextBlock> 

         <TextBlock.Text> 

             <MultiBinding StringFormat="{}{1}, {0}" > 

                   <Binding Path="EmpFirstName" /> 

                   <Binding Path="EmpLastName" /> 

             </MultiBinding>

         </TextBlock.Text>

    </TextBlock>

</DataTemplate>

SelectionChanged: (I do plan to implement commanding before long but, as this is my first WPF project I have not gone full MVVM yet. I am trying to take things in small-medium sized bites)

// This is done this way to maintain the DataContext Integrity 

// and avoid an error due to an Object being "Not New" in Linq-to-SQL

private void ownerComboBox_SelectionChanged(object sender, 

                                            SelectionChangedEventArgs e)

{

    Employee currentEmpl = ownerComboBox.SelectedItem as Employee;

    if (currentEmpl != null && 

        currentEmpl != statusBoardViewModel.SelectedIssue.Employee2)

    {

        statusBoardViewModel.SelectedIssue.Employee2 = currentEmpl;

    }

}

Your getting this error because when you validation finds that there are no issues, the Errors collection returns with no items, and the following binding logic fails:

Path=(Validation.Errors)[0].ErrorContent}"

you are accessing the validation collection by a specific index. I'm currently working on a DataTemplate Suggestion for replacing this text.

I love that Microsoft listed this in their standard example of a validation template.

update so replace the code above with the following, and the binding logic will know how to handle the empty validationresult collection:

Path=(Validation.Errors).CurrentItem.ErrorContent}"

(following xaml was added as a comment)

<ControlTemplate x:Key="ValidationErrorTemplate" TargetType="Control">

    <StackPanel Orientation="Horizontal">

        <TextBlock Foreground="Red" FontSize="24" Text="*" 

                   ToolTip="{Binding .CurrentItem}">

        </TextBlock>

        <AdornedElementPlaceholder>

        </AdornedElementPlaceholder>

    </StackPanel>

</ControlTemplate>

I think this is the best way:

Path=(Validation.Errors)/ErrorContent

/ is actually equal to CurrentItem by @Nathan

In my case, CurrentItem is a no go.

Try the converter for converting to a multi-line string as described here

I've seen the code you're using posted in multiple places, but it seems odd to me that

Path=(Validation.Errors)[0].ErrorContent}

doesn't raise any red flags. But I'm also new to WPF and perhaps there is some secret to making that work in every case.

Rather than attempting to index a possibly empty collection with an array index, add a converter that returns the first error in the list.

In my case, I was getting this exception when I tried to apply @Nation Tregillus' solution:

Cannot resolve property 'CurrentItem' in data context of type
'System.Collections.ObjectModel.ReadOnlyObservableCollection'

So I went with @Altiano Gerung's solution instead, where my code ended up being:

<ControlTemplate x:Key="ValidationErrorTemplate">

    <DockPanel Margin="5,0,36,0">

        <StackPanel Orientation="Horizontal" VerticalAlignment="Top" DockPanel.Dock="Right"

                    Margin="5,0,36,0"

                    ToolTip="{Binding ElementName=ErrorAdorner, Path=AdornedElement.(Validation.Errors)/ErrorContent}"

                    ToolTipService.ShowDuration="300000"

                    ToolTipService.InitialShowDelay="0"

                    ToolTipService.BetweenShowDelay="0"

                    ToolTipService.VerticalOffset="-75"

                    >

CurrentItem did not work for me either But
@Nathtan's answer worked for my situation where I have a custom textBox resource. Thanks @Nathan I spent an hour on this.

<Style.Triggers>

  <Trigger Property="Validation.HasError" Value="true">

    <Setter Property="ToolTip"

        Value="{Binding RelativeSource={x:Static RelativeSource.Self},

        Path=(Validation.Errors)/ErrorContent}" />

  </Trigger>

</Style.Triggers>