How to pass a static value to IValueConverter in XAML

Question

I would like to use static texts fetched from a web service in my WP7 app. Each text has a Name (the indetifier) and a Content property.

For example a text could look like this:

Name = "M43";
Content = "This is the text to be shown";

I would then like to pass the Name (i.e. the identifier) of the text to an IValueConverter, which would then look up the the Name and return the text.

I figured the converter to look something like this:

public class StaticTextConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value != null)
        {
            return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(value)).Content;
        }

        return null;
    }
}

Then in the XAML:

<phone:PhoneApplicationPage.Resources>
    <Helpers:StaticTextConverter x:Name="StaticTextConverter" />
</phone:PhoneApplicationPage.Resources>

...

<TextBlock Text="{Binding 'M43', Converter={StaticResource StaticTextConverter}}"/>

However, this does not seem to work and I am not sure that I pass in the value to the converter correctly.

Does anyone have some suggestions?

Answer 1

I finally found the answer. The answer was a mix between that of @Shawn Kendrot and another question I asked here: IValueConverter not getting invoked in some scenarios

To summarize the solution for using the IValueConverter I have to bind my control in the following manor:

<phone:PhoneApplicationPage.Resources>
    <Helpers:StaticTextConverter x:Name="TextConverter" />
</phone:PhoneApplicationPage.Resources>

<TextBlock Text="{Binding Converter={StaticResource TextConverter}, ConverterParameter=M62}" />

Since the ID of the text is passed in with the converter parameter, the converter looks almost the same:

public class StaticTextConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (parameter != null && parameter is string)
        {
            return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(parameter)).Content;
        }

        return null;
    }
}

However, as it turns out, the binding and thus the converter is not invoked if it does not have a DataContext. To solve this, the DataContext property of the control just has to be set to something arbitrary:

<TextBlock DataContext="arbitrary" 
           Text="{Binding Converter={StaticResource TextConverter}, ConverterParameter=M62}" />

And then everything works as intended!

Answer 2

The problem lies in your binding. It will check the DataContext, and on this object, it will try to evaluate the properties M62 and ValueboxConsent on that object.

You might want to add static keys somewhere in your application where you can bind to:

<TextBlock Text="{Binding Source="{x:Static M62.ValueboxConsent}", Converter={StaticResource StaticTextConverter}}" />

Where M62 is a static class where your keys are located.. like so:

public static class M62
{
    public static string ValueboxConsent
    {
        get { return "myValueBoxConsentKey"; }
    }
}

Answer 3

If you want to use a value converter, you'll need to pass the string to the parameter of value converter

Xaml:

<TextBlock Text="{Binding Converter={StaticResource StaticTextConverter}, ConverterParameter=M43}"/>

Converter:

public class StaticTextConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (parameter != null)
        {
            return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(parameter)).Content;
        }

        return null;
    }
}

Answer 4

xmlns:prop="clr-namespace:MyProj.Properties;assembly=namespace:MyProj"

<TextBlock Text="{Binding Source={x:Static prop:Resources.MyString}, Converter={StaticResource StringToUpperCaseConverter}}" />