You could assign each of the RadioButtons a unique name and use a MultiBinding with ElementName and a converter:
<Grid Grid.ColumnSpan="2" Grid.Row="1" HorizontalAlignment="Center">
<RadioButton x:Name="r1" IsChecked="{Binding SelectedLetter, ConverterParameter='A', Converter={StaticResource InputLetterToBooleanConverter}, Mode=TwoWay}"
Content="A" HorizontalAlignment="Left" VerticalAlignment="Top" Width="48.5" Height="45" Style="{DynamicResource RadioButtonInputs}" FontSize="36" Padding="0" Background="{x:Null}" BorderBrush="{x:Null}" Foreground="{DynamicResource BrushLetterA}" Cursor="Hand"/>
<RadioButton x:Name="r2" IsChecked="{Binding SelectedLetter, ConverterParameter='B', Converter={StaticResource InputLetterToBooleanConverter}, Mode=TwoWay}"
Content="B" HorizontalAlignment="Left" Margin="53.5,0,0,0" VerticalAlignment="Top" Width="48.5" Height="45" Style="{DynamicResource RadioButtonInputs}" FontSize="36" Padding="0" Background="{x:Null}" BorderBrush="{x:Null}" Foreground="{DynamicResource BrushLetterB}" Cursor="Hand"/>
<RadioButton x:Name="r3" IsChecked="{Binding SelectedLetter, ConverterParameter='C', Converter={StaticResource InputLetterToBooleanConverter}, Mode=TwoWay}"
Content="C" HorizontalAlignment="Left" Margin="107,0,0,0" VerticalAlignment="Top" Width="48.5" Height="45" Style="{DynamicResource RadioButtonInputs}" FontSize="36" Padding="0" Background="{x:Null}" BorderBrush="{x:Null}" Foreground="{DynamicResource BrushLetterC}" Cursor="Hand"/>
<RadioButton x:Name="r4" IsChecked="{Binding SelectedLetter, ConverterParameter='D', Converter={StaticResource InputLetterToBooleanConverter}, Mode=TwoWay}"
Content="D" HorizontalAlignment="Left" Margin="160.5,0,0,0" VerticalAlignment="Top" Width="48.5" Height="45" Style="{DynamicResource RadioButtonInputs}" FontSize="36" Padding="0" Background="{x:Null}" BorderBrush="{x:Null}" Foreground="{DynamicResource BrushLetterD}" Cursor="Hand"/>
</Grid>
<Slider Minimum="10" Maximum="{Binding MaximumZoom}" Value="{Binding Zoom, Mode=TwoWay}"
Name="zoom" Margin="20.508,22.333,0,0">
<Slider.IsEnabled>
<MultiBinding Converter="{StaticResource myConverter}">
<Binding ElementName="r1" Path="IsChecked"/>
<Binding ElementName="r2" Path="IsChecked"/>
<Binding ElementName="r3" Path="IsChecked"/>
<Binding ElementName="r4" Path="IsChecked"/>
</MultiBinding>
</Slider.IsEnabled>
</Slider>
public class MyConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
foreach (object value in values)
{
bool b = System.Convert.ToBoolean(value);
if (b)
return true;
}
return false;
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
