Convert y / n to true / false in XAML

Question

I used the following code to preselect some rows in a listbox:

<ListBox.ItemContainerStyle>
    <Style TargetType="{x:Type ListBoxItem}">
       <Setter Property="IsSelected" Value="{Binding f_selected, Mode=OneWay}" />
    </Style>
</ListBox.ItemContainerStyle>

The value of f_selected in the code can be only true or false, but on the DB the values are y/n. I've used a trick to convert y/n to true/false by using an object, but higher heads have asked me to work only with y/n in the objects. Is there any way to work with a string instead of a bool or to do the conversion in the XAML or the viewmodel?

Thanks for the help and as always sorry for the bad english.

Do you know the why of the requirement that only strings should be used. That might give away how this should be implemented. — Emond, Apr 05 '19 at 14:49

Timo Salomäki · Answer 1 · 2019-04-05T14:33:48.727

Note: mm8's answer using DataTrigger's is great if you're developing a WPF application.

In WPF and UWP, you can create a custom implementation of the IValueConverter interface to achieve this with almost the same code. Basically, it will transform your string input to a boolean depending on the rules you define.

WPF:

public class StringToBooleanConverter: IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value.ToString().Equals("y");
    }

    // This is not really needed because you're using one way binding but it's here for completion
    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if(value is bool)
        {
            return value ? "y" : "n";
        }
    }
}

UWP:

The above code is exactly the same except for the last parameter in Convert and ConvertBack methods:

public object Convert(object value, Type targetType, object parameter, string language) { }

public object ConvertBack(object value, Type targetType, object parameter, string language) { }

The following is more or less the same for both WPF and UWP. You can use the converter in XAML to convert from string to bool:

<ListBox.ItemContainerStyle>
    <Style TargetType="{x:Type ListBoxItem}">
       <Setter Property="IsSelected" Value="{Binding f_selected, Mode=OneWay, Converter={StaticResource StringToBooleanConverter}}" />
    </Style>
</ListBox.ItemContainerStyle>

Also, remember to introduce the converter in the beginning:

<Window.Resources>
    <local:YesNoToBooleanConverter x:Key="StringToBooleanConverter" />
</Window.Resources>

score 0 · Accepted Answer · answered Apr 05 '19 at 14:12

In WPF you could use a DataTrigger:

<ListBox.ItemContainerStyle>
    <Style TargetType="{x:Type ListBoxItem}">
        <Style.Triggers>
            <DataTrigger Binding="{Binding f_selected}" Value="y">
                <Setter Property="IsSelected" Value="True" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
</ListBox.ItemContainerStyle>

In UWP you could accomplish the same thing using a DataTriggerBehavior.

Convert y / n to true / false in XAML

2 Answers2