c# - Issue with WPF validation(IDataErrorInfo) and tab focusing

Question

I have a TextBox bound to a property of an object which implements IDataErrorInfo. I set up the Validation.ErrorTemplate of the TextBox, and it works fine. The problem is that I have these on a TabControl, and the validation template doesn't display any more if I change the tab to another one and then come back to the initial tab (where the TextBox is). It looks like it is validated(like the value is correct), but actually it is not.

This is the IDataErrorInfo object - note that a "correct" value is a string with a length of 2:

public class Presenter : IDataErrorInfo
{
    public Presenter()
    {
        this.Property = String.Empty;
    }

    public string Property { get; set; }

    public string Error { get { return null; } }

    public string this[string columnName]
    {
        get
        {
             if (columnName == "Property")
             {
                if (this.Property.Length == 2)
                   return null;
                else
                   return "Invalid property length!";
             }
             else return null;
        }
    }
}

and this is the XAML:

<TabControl >
    <TabItem Header="tabItem1" Name="tabItem1" GotFocus="tabItem1_GotFocus">
        <Grid>
            <TextBox Width="100" Height="20" x:Name="txtField">
                <TextBox.Style>
                    <Style TargetType="{x:Type TextBox}">
                        <Setter Property="Validation.ErrorTemplate">
                            <Setter.Value>
                            <ControlTemplate>
                                <Grid>
                                    <Grid.ColumnDefinitions>
                                        <ColumnDefinition Width="Auto"/>
                                        <ColumnDefinition Width="16"/>
                                    </Grid.ColumnDefinitions>
                                    <AdornedElementPlaceholder Grid.Column="0"/>
                                    <Image Source="bullets16.png" Grid.Column="1" ToolTip="{Binding CurrentItem.ErrorContent, Mode=OneWay}">
                                    </Image>
                                </Grid>
                            </ControlTemplate>
                            </Setter.Value>
                        </Setter>
                    </Style>
                </TextBox.Style>
                <TextBox.Text>
                    <Binding Path="Property" UpdateSourceTrigger="PropertyChanged" ValidatesOnDataErrors="True">
                    </Binding>
                </TextBox.Text>
            </TextBox>
        </Grid>
    </TabItem>
    <TabItem Header="tabItem2" Name="tabItem2" >
        <Grid />
    </TabItem>
</TabControl>

Any ideas on what I am doing wrong?

Answer 1

Tab items tend to mess up with adorners (although I don't know why, I experienced it).

I could reproduce your problem.

Solve it by wrapping the contents of the TabItem with an AdornerDecorator.

So:

<TabControl >
    <TabItem Header="tabItem1" Name="tabItem1" GotFocus="tabItem1_GotFocus">

        <AdornerDecorator>

           <Grid>
           ....
           </Grid>

        </AdornerDecorator>

    </TabItem>
    ...
</TabControl>