Converter

Built-in converter

BooleanToVisibilityConverter

BooleanToVisibilityConverter is located in System.Windows.Controls.

<Window> <Window.Resources> <BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter" /> </Window.Resources> <TextBlock Visibility="{Binding IsVisible, Converter={StaticResource BooleanToVisibilityConverter}}" />

ValueConverter

<UserControl xmlns:conversion="clr-namespace:MyNamespace.Conversion"> <UserControl.Resources> <conversion:ListToVisibilityConverter x:Key="ListToVisibilityConverter" /> </UserControl.Resources> <TextBlock Visibility="{Binding MyList, Converter={StaticResource ListToVisibilityConverter}}" />

ListToVisibilityConverter.cs

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; } } }

Inverted convertion

Inverted convertion with IsInverted property

<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}}" />

ListToVisibilityConverter.cs

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(); } } }

Inverted convertion with ConverterParameter

The ConverterParameter property can not be bound because it is not a dependency property. Use MultiValueConverter as an alternative.

<TextBlock Visibility="{Binding MyList, Converter={StaticResource ListToVisibilityConverter}, ConverterParameter=Inverted}" />

ListToVisibilityConverter.cs

[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 }

MultiValueConverter

<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>

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(); } } }

Examples

BooleanToCursorConverter

[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(); } }

MyWindow.xaml

<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>