Class property declaration in XAML - xaml

Question

I am confused in XAML namespace declaration.
Please help to clarify my case. I have class BooleanToObjectConverter : IValueConverter in CoTraveller namespace:
public class EmailValidatorBehavior : Behavior<Entry>
{
const string digitRegex = #"^(?("")("".+?(?<!\\)""#)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])#))" +
#"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9][\-a-z0-9]{0,22}[a-z0-9]))$";
static readonly BindablePropertyKey IsValidPropertyKey = BindableProperty.CreateReadOnly("IsValid", typeof(bool), typeof(EmailValidatorBehavior), false);
public static readonly BindableProperty IsValidProperty = IsValidPropertyKey.BindableProperty;
static readonly BindablePropertyKey IsVisiblePropertyKey = BindableProperty.CreateReadOnly("IsVisible", typeof(bool), typeof(EmailValidatorBehavior), false);
public static readonly BindableProperty IsVisibleProperty = IsVisiblePropertyKey.BindableProperty;
public bool IsValid
{
get { return (bool)base.GetValue(IsValidProperty); }
private set { base.SetValue(IsValidPropertyKey, value); }
}
public bool IsVisible
{
get { return (bool)base.GetValue(IsVisibleProperty); }
private set { base.SetValue(IsVisiblePropertyKey, value); }
}
protected override void OnAttachedTo(Entry entry)
{
entry.TextChanged += OnEntryTextChanged;
base.OnAttachedTo(entry);
}
protected override void OnDetachingFrom(Entry entry)
{
entry.TextChanged -= OnEntryTextChanged;
base.OnDetachingFrom(entry);
}
void OnEntryTextChanged(object sender, TextChangedEventArgs e)
{
if (e.NewTextValue.Length > 0)
{
IsVisible = true;
Entry entry = (Entry)sender;
IsValid = Regex.IsMatch(e.NewTextValue, digitRegex);
if (IsValid) // Check only if we have a valid email
{
// Here we validate if the email contains our requirements
String email = entry.Text;
int pos = email.IndexOf("#"); // Exclude the domain
string username = email.Substring(0, pos);
if (username.Contains(FRIEND) || username.Contains(FRIENDS))
{
IsValid = true;
}
else
IsValid = false;
}
}
else
IsVisible = false;
}
public class BooleanToObjectConverter<Image> : IValueConverter
{
public Image FalseObject { set; get; }
public Image TrueObject { set; get; }
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
return (bool)value ? this.TrueObject : this.FalseObject;
}
//public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
//{
// throw new NotImplementedException();
//}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
return ((Image)value).Equals(this.TrueObject);
}
//public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
//{
// throw new NotImplementedException();
//}
}
}
I want to use FalseObject and TrueObject properties in App resources like:
<Application
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="CoTraveller.RegistrationPage"
xmlns:local="clr-namespace:CoTraveller">
<Application.Resources>
<!-- Application resource dictionary -->
<ResourceDictionary>
<local:BooleanToObjectConverter x:Key="boolToStyleImage"
x:TypeArguments="Style">
<local:BooleanToObjectConverter.FalseObject>
<Style TargetType="Image">
<Setter Property="HeightRequest" Value="24" />
<Setter Property="Source"
Value="your_wrong_image_here.png" />
</Style>
</local:BooleanToObjectConverter.FalseObject>
<x:BooleanToObjectConverter.TrueObject>
<Style TargetType="Image">
<Setter Property="HeightRequest" Value="24" />
<Setter Property="Source"
Value="your_correct_image_here.png" />
</Style>
</x:BooleanToObjectConverter.TrueObject>
</local:BooleanToObjectConverter>
</ResourceDictionary>
</Application.Resources>
</Application>
but have error: Severity Code Description Project File Line Suppression State
Error XLS0415 The attachable property 'FalseObject' was not found in type 'BooleanToObjectConverter'. CoTraveller App.xaml 11
What is the problem?

Answer 1

Derive from DependencyObject in order to be able to use the bindable DependencyProperties:
public class BooleanToObjectConverter: DependencyObject, IValueConverter
{
public Image FalseObject
{
get
{
return (Image)GetValue(FalseObjectProperty);
}
set
{
SetValue(FalseObjectProperty, value);
}
}
public static readonly DependencyProperty FalseObjectProperty =
DependencyProperty.Register(
"FalseObject",
typeof(Image),
typeof(BooleanToObjectConverter<Image>),
new PropertyMetadata(null));
public Image TrueObject
{
get
{
return (Image)GetValue(TrueObjectProperty);
}
set
{
SetValue(TrueObjectProperty, value);
}
}
public static readonly DependencyProperty TrueObjectProperty =
DependencyProperty.Register(
"TrueObject",
typeof(Image),
typeof(BooleanToObjectConverter<Image>),
new PropertyMetadata(null));
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
return (bool)value ? this.TrueObject : this.FalseObject;
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
return ((Image)value).Equals(this.TrueObject);
}
}
Side note: The use of the generic here doesn't make a lot of sense so I removed it.
If the original intention was to do use an actual generic type see: Generic Type in Xaml Resources because it is not that straight forward to specify a generic type argument for entries in a resources dictionary.