Silverlight - Button control tab stop twice mystery

Question

I'm debugging a large Silverlight application and i'm finding on every form all button controls receive tab focus twice before going to next control. I cannot reproduce this behavior in a simple hello world application though. Interestingly this problem does not occur on HyperlinkButton controls in the same form, just Button. Any idea what would cause this, or some things to help me isolate the cause of this?

Thanks in advance.

[Edit]

If I set the IsTabStop property to false then it just tabs on the button one time. I hesitate to use this as a fix as I really would like to know what the source of the problem is.

I've traced the problem to the Implicit button style that we're using in a resource file. I would really like to know why this XAML causes this to happen.

Implicit Button Style XAML

<Style TargetType="Button" x:Key="DefaultButtonStyle">
    <Setter Property="Background" Value="{StaticResource NormalBrush}"/>
    <Setter Property="Foreground" Value="{StaticResource TextContentBrush}"/>
    <Setter Property="FontFamily" Value="{StaticResource ContentFontFamily}"/>
    <Setter Property="FontSize" Value="{StaticResource ContentFontSize}"/>
    <Setter Property="Padding" Value="3"/>
        <Setter Property="Padding" Value="10,3,10,3" />
    <Setter Property="BorderThickness" Value="1"/>
    <Setter Property="BorderBrush" Value="{StaticResource NormalBorderBrush}"/>
    <Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="Button">
<Grid x:Name="grid" RenderTransformOrigin="0.5,0.5">
    <Grid.RenderTransform>
        <TransformGroup>
            <ScaleTransform/>
            <SkewTransform/>
            <RotateTransform/>
            <TranslateTransform/>
        </TransformGroup>
    </Grid.RenderTransform>
    <VisualStateManager.VisualStateGroups>
        <VisualStateGroup x:Name="CommonStates">
            <VisualStateGroup.Transitions>
                <VisualTransition From="MouseOver" GeneratedDuration="0:0:0.1" To="Pressed">
                    <VisualTransition.GeneratedEasingFunction>
                        <ExponentialEase EasingMode="EaseIn" Exponent="-2"/>
                    </VisualTransition.GeneratedEasingFunction>
                </VisualTransition>
                <VisualTransition From="Pressed" GeneratedDuration="0:0:0.1" To="MouseOver">
                    <VisualTransition.GeneratedEasingFunction>
                        <ExponentialEase EasingMode="EaseOut" Exponent="0"/>
                    </VisualTransition.GeneratedEasingFunction>
                </VisualTransition>
                <VisualTransition From="Normal" GeneratedDuration="0:0:0.01" To="MouseOver">
                    <VisualTransition.GeneratedEasingFunction>
                        <ExponentialEase EasingMode="EaseIn" Exponent="7"/>
                    </VisualTransition.GeneratedEasingFunction>
                </VisualTransition>
                <VisualTransition From="MouseOver" GeneratedDuration="0:0:0.1" To="Normal">
                    <VisualTransition.GeneratedEasingFunction>
                        <CircleEase EasingMode="EaseIn"/>
                    </VisualTransition.GeneratedEasingFunction>
                </VisualTransition>
            </VisualStateGroup.Transitions>
            <VisualState x:Name="Normal"/>
            <VisualState x:Name="MouseOver">
                <Storyboard>
                    <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="MouseOverBorder">
                        <EasingDoubleKeyFrame KeyTime="0" Value="1"/>
                    </DoubleAnimationUsingKeyFrames>
                    <ColorAnimationUsingKeyFrames Storyboard.TargetProperty="(Control.Foreground).(SolidColorBrush.Color)" Storyboard.TargetName="contentPresenter">
                        <EasingColorKeyFrame KeyTime="0" Value="{StaticResource BaseColor2}"/>
                    </ColorAnimationUsingKeyFrames>
                </Storyboard>
            </VisualState>
            <VisualState x:Name="Pressed">
                <Storyboard>
                    <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="PressedBorder" Storyboard.TargetProperty="(UIElement.Opacity)">
                        <SplineDoubleKeyFrame KeyTime="00:00:00.1000000" Value="1.0" KeySpline="0,0,0.0299999993294477,0.920000016689301"/>
                    </DoubleAnimationUsingKeyFrames>
                    <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[0].(ScaleTransform.ScaleX)" Storyboard.TargetName="grid">
                        <EasingDoubleKeyFrame KeyTime="0:0:0.01" Value="1.05"/>
                    </DoubleAnimationUsingKeyFrames>
                    <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[0].(ScaleTransform.ScaleY)" Storyboard.TargetName="grid">
                        <EasingDoubleKeyFrame KeyTime="0:0:0.01" Value="1.05"/>
                    </DoubleAnimationUsingKeyFrames>
                    <ColorAnimationUsingKeyFrames Storyboard.TargetProperty="(Control.Foreground).(SolidColorBrush.Color)" Storyboard.TargetName="contentPresenter">
                        <EasingColorKeyFrame KeyTime="0" Value="{StaticResource BaseColor2}"/>
                    </ColorAnimationUsingKeyFrames>
                </Storyboard>
            </VisualState>
            <VisualState x:Name="Disabled">
                <Storyboard>
                    <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="DisabledVisualElement" Storyboard.TargetProperty="(UIElement.Opacity)">
                        <SplineDoubleKeyFrame KeyTime="00:00:00.1000000" Value="0.75"/>
                    </DoubleAnimationUsingKeyFrames>
                    <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="contentPresenter" Storyboard.TargetProperty="(UIElement.Opacity)">
                        <SplineDoubleKeyFrame KeyTime="00:00:00.1000000" Value="0.3"/>
                    </DoubleAnimationUsingKeyFrames>
                </Storyboard>
            </VisualState>
        </VisualStateGroup>
        <VisualStateGroup x:Name="FocusStates">
            <VisualState x:Name="Focused" >
                <Storyboard>
                    <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="FocusVisualElement" Storyboard.TargetProperty="(UIElement.Opacity)">
                        <SplineDoubleKeyFrame KeyTime="00:00:00" Value="1.0" />
                    </DoubleAnimationUsingKeyFrames>
                </Storyboard>
            </VisualState>
            <VisualState x:Name="Unfocused"/>
        </VisualStateGroup>
    </VisualStateManager.VisualStateGroups>
    <Border x:Name="BaseBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="1" CornerRadius="1" >
        <Border.Background>
            <SolidColorBrush Color="{StaticResource BaseColor7}"/>
        </Border.Background>
        <Grid>
            <Border x:Name="Background" BorderBrush="{StaticResource NormalInnerBorderBrush}" Background="{TemplateBinding Background}"/>
            <Border x:Name="MouseOverBorder" Opacity="0" Background="{StaticResource MouseOverBrush}" Margin="-0.5,-0.5,0.5,0.5"/>
            <Border x:Name="PressedBorder" BorderThickness="{TemplateBinding BorderThickness}" Opacity="0" Background="{StaticResource MouseOverBrush}" RenderTransformOrigin="0.5,0.5" Margin="-1">
                <Border.RenderTransform>
                    <TransformGroup>
                        <ScaleTransform/>
                        <SkewTransform/>
                        <RotateTransform/>
                        <TranslateTransform/>
                    </TransformGroup>
                </Border.RenderTransform>
            </Border>
        </Grid>
    </Border>
    <Rectangle x:Name="DisabledVisualElement" Fill="{StaticResource DisabledBackgroundBrush}" IsHitTestVisible="false" Opacity="0" RadiusY="1" RadiusX="1" Stroke="{StaticResource DisabledBackgroundBrush}"/>
    <ContentControl x:Name="contentPresenter" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" Foreground="{TemplateBinding Foreground}" Padding="2" />
    <Rectangle x:Name="FocusVisualElement" Stroke="{StaticResource FocusedBrush}" Margin="-1" Opacity="0" /> <!--IsHitTestVisible="false"-->
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 1

Probably there is something on your Button's template that has IsTabStop set to true.

How complex is your template? Try resetting to the default template to see if that solves your problem.

Answer 2

Try setting the IsTabStop property of the ContentControl in your template to False:

<ContentControl x:Name="contentPresenter" IsTabStop="False" (...) />