Built-in converter
BooleanToVisibilityConverter
BooleanToVisibilityConverter is located in System.Windows.Controls.
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<Window>
<Window.Resources>
<BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter" />
</Window.Resources>
<TextBlock Visibility="{Binding IsVisible, Converter={StaticResource BooleanToVisibilityConverter}}" />
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InvertedBooleanToVisibilityConverter
| InvertedBooleanToVisibilityConverter.cs
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public class InvertedBooleanToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var flag = false;
if (!(value is bool flag) && value is bool? nullable)
{
flag = nullable.Value;
}
return (object) (Visibility) (flag ? 2 : 0);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
=> (object) (bool) (!(value is Visibility visibility) ? 0 : (visibility == Visibility.Collapsed ? 1 : 0));
}
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ValueConverter
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<UserControl xmlns:conversion="clr-namespace:MyNamespace.Conversion">
<UserControl.Resources>
<conversion:ListToVisibilityConverter x:Key="ListToVisibilityConverter" />
</UserControl.Resources>
<TextBlock Visibility="{Binding MyList, Converter={StaticResource ListToVisibilityConverter}}" />
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| ListToVisibilityConverter.cs
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namespace MyNamespace.Conversion
{
// L'attribut ValueConversion est optionel,
// il permet de spécifier le type d'entrée et le type de sortie
[ValueConversion(typeof(IEnumerable), typeof(Visibility))]
public class ListToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is IEnumerable itemCollection)
{
return itemCollection.Cast<object>().Any() ? Visibility.Visible : Visibility.Collapsed;
}
return DependencyProperty.UnsetValue;
}
// Conversion inverse non-implémentée
public object ConvertBack(object value, Type targetTypes, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
throw new NotSupportedException();
return null;
}
}
}
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Inverted convertion
Inverted convertion with IsInverted property
|
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<UserControl xmlns:conversion="clr-namespace:MyNamespace.Conversion">
<UserControl.Resources>
<conversion:ListToVisibilityConverter x:Key="EmptyListToCollapsedConverter" />
<conversion:ListToVisibilityConverter x:Key="EmptyListToVisibleConverter"
IsInverted="true" />
</UserControl.Resources>
<TextBlock Visibility="{Binding MyList, Converter={StaticResource EmptyListToCollapsedConverter}}" />
<TextBlock Visibility="{Binding MyList, Converter={StaticResource EmptyListToVisibleConverter}}" />
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| ListToVisibilityConverter.cs
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namespace MyNamespace.Conversion
{
[ValueConversion(typeof(IEnumerable), typeof(Visibility))]
public class ListToVisibilityConverter : IValueConverter
{
public bool IsInverted { get; set; }
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var visibleFlag = false;
if (value is IEnumerable itemCollection)
{
visibleFlag = itemCollection.Cast<object>().Any();
}
else
{
return DependencyProperty.UnsetValue;
}
if (this.IsInverted)
{
visibleFlag = !visibleFlag;
}
return visibleFlag ? Visibility.Visible : Visibility.Collapsed;
}
// Conversion inverse non-implémentée
public object ConvertBack(object value, Type targetTypes, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
}
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The ConverterParameter property can not be bound because it is not a dependency property.
Use MultiValueConverter as an alternative. |
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<TextBlock Visibility="{Binding MyList, Converter={StaticResource ListToVisibilityConverter}, ConverterParameter=Inverted}" />
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| ListToVisibilityConverter.cs
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[ValueConversion(typeof(IEnumerable), typeof(Visibility))]
public class ListToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var visibleFlag = false;
if (value is IEnumerable itemCollection)
{
visibleFlag = itemCollection.Cast<object>().Any();
}
else
{
return DependencyProperty.UnsetValue;
}
if (parameter != null && Enum.TryParse(parameter.ToString(), true, out Parameters invert) && invert == Parameters.Inverted)
{
visibleFlag = !visibleFlag;
}
return visibleFlag ? Visibility.Visible : Visibility.Collapsed;
}
// Conversion inverse non-implémentée
public object ConvertBack(object value, Type targetTypes, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
private enum Parameters
{
Normal,
Inverted
}
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MultiValueConverter
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<UserControl xmlns:conversion="clr-namespace:MyNamespace.Conversion">
<UserControl.Resources>
<conversion:TakeItemsConverter x:Key="TakeItemsConverter"/>
</UserControl.Resources>
<ItemsControl>
<ItemsControl.ItemsSource>
<MultiBinding Converter="{StaticResource TakeItemsConverter}">
<Binding Path="Items" />
<Binding Path="MaxNumberOfItemsToDisplay" />
</MultiBinding>
</ItemsControl.ItemsSource>
</ItemsControl>
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namespace MyNamespace.Conversion
{
// L'attribut ValueConversion n'est pas utilisé ici car il n'est pas adapté
// au MultiValueConverter : il ne peut définir qu'un seul type d'entrée
public class TakeItemsConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
// expect 2 values, an IEnumerable and an int
if (values != null
&& values.Length == 2
&& values[0] is IEnumerable itemCollection
&& values[1] != null
&& int.TryParse(values[1].ToString(), NumberStyles.Integer, culture, out var numberOfItemsToTake))
{
return itemCollection.Cast<object>().Take(numberOfItemsToTake);
}
return DependencyProperty.UnsetValue;
}
// Conversion inverse non-implémentée
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
}
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Examples
BooleanToCursorConverter
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[ValueConversion(typeof(bool), typeof(Cursor))]
public sealed class BooleanToCursorConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is bool isBusy)
{
return isBusy ? Cursors.Wait : Cursors.Arrow;
}
return DependencyProperty.UnsetValue;
}
public object ConvertBack(object value, Type targetTypes, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
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| MyWindow.xaml
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<Window xmlns:converters="clr-namespace:MyApp.Converters">
<Window.Resources>
<converters:BooleanToCursorConverter x:Key="BooleanToCursorConverter" />
</Window.Resources>
<!-- has to be defined after the converter -->
<Window.Cursor>
<Binding Path="IsBusy"
Converter="{StaticResource BooleanToCursorConverter}" />
</Window.Cursor>
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