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Passing two command parameters using a WPF binding
I have the following hierarchy:
abstract class TicketBase
{
public DateTime PublishedDate { get; set; }
}
class TicketTypeA:TicketBase
{
public string PropertyA { get; set; }
}
class TicketTypeB:TicketBase
{
public string PropertyB { get; set; }
}
In my VM I have a List<TicketBase> Tickets. When a user clicks a button on my app, they want to see a list of previous values of a certain property, e.g.:
<Button Tag="{x:Type Types:TicketTypeA}"
Command="{Binding ListHistoryCommand}"
CommandParameter="{Binding Tag, RelativeSource={RelativeSource Self}}" />
as you can see, I set my Tag property to TicketTypeA and pass that as parameter to my command:
private void ListHistory(object o)
{
if (Tickets.Count == 0)
return;
Type ty = o as Type;
ValueHistory = new ObservableCollection<TicketBase>(GetTicketsOfType(ty).Select(t => t)); // <- Need to return t.PropertyA here, but dynamically
}
IEnumerable<TicketBase> GetTicketsOfType(Type type)
{
if (!typeof(TicketBase).IsAssignableFrom(type))
throw new ArgumentException("Parameter 'type' is not a TicketBase");
return Tickets.Where(p => p.GetType() == type);
}
(ValueHistory is another collection that I set as ItemsSource on my grid)
However I need to also pass in the property name too, so that I can display just that property in the grid like so:
Published Time | PropertyA
===================================================
09:00 | <value of PropertyA at 09:00>
08:55 | <value of PropertyA at 08:55>
So the question is basically what is the cleanest way to pass in the property name as another parameter into my command?
See this question
Passing two command parameters using a WPF binding
Update
If you need to store both the Type and the Property Name on the Button you'll have to use an attached property like you said. To pass the two parameters to the Command, something like this should work
<Button Tag="{x:Type Types:TicketTypeA}"
local:ParameterNameBehavior.ParameterName="{Binding Source='Parameter A'}"
Command="{Binding ListHistoryCommand}">
<Button.CommandParameter>
<MultiBinding Converter="{StaticResource PassThroughConverter}">
<Binding Path="Tag" RelativeSource="{RelativeSource Self}"/>
<Binding Path="(local:ParameterNameBehavior.ParameterName)"
RelativeSource="{RelativeSource Self}"/>
</MultiBinding>
</Button.CommandParameter>
</Button>
ParameterNameBehavior
public static class ParameterNameBehavior
{
private static readonly DependencyProperty ParameterNameProperty =
DependencyProperty.RegisterAttached("ParameterName",
typeof(string),
typeof(ParameterNameBehavior));
public static void SetParameterName(DependencyObject element, string value)
{
element.SetValue(ParameterNameProperty, value);
}
public static string GetParameterName(DependencyObject element)
{
return (string)element.GetValue(ParameterNameProperty);
}
}
PassThroughConverter
public class PassThroughConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
return values.ToList();
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
throw new NotSupportedException();
}
}
I got this working without resorting to Attached Properties by using the x:Name property in the Xaml and then passing this on to my CommandParameter as a MultiBinding along with the Tag. From Front to Back:
In my View:
<Button Content="{Binding PropertyA}" x:Name="PropertyA" Tag="{x:Type Types:TicketTypeA}" Style="{StaticResource LinkButton}"/>
<Button Content="{Binding PropertyB}" x:Name="PropertyB" Tag="{x:Type Types:TicketTypeB}" Style="{StaticResource LinkButton}"/>
In the style for each button:
<Style x:Key="LinkButton" TargetType="Button">
<Setter Property="Command" Value="{Binding DataContext.ListHistoryCommand, Mode=OneWay, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}}" />
<Setter Property="CommandParameter">
<Setter.Value>
<MultiBinding Converter="{StaticResource propertyConverter}">
<MultiBinding.Bindings>
<Binding Path="Tag" RelativeSource="{RelativeSource Mode=Self}"/>
<Binding Path="Name" RelativeSource="{RelativeSource Mode=Self}"/>
</MultiBinding.Bindings>
</MultiBinding>
</Setter.Value>
</Setter>
In my Converter:
public class PropertyConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
//Type t = values[0] as Type;
//String propName = values[1] as string;
Type t = values[0] as Type;
if (t == null)
return typeof(TicketBase);
String s = values[1] as String;
return new Tuple<Type,String>(t,s);
}
}
In my View Model:
private void ListHistory(object o)
{
if (Tickets.Count == 0)
return;
var tuple = o as Tuple<Type,String>;
// Now write some code to dynamically select the propertyName (tuple.Item2) from the type (tuple.Item1)
}
I am now receiving the Type and PropertyName in my Command. Now, I just need to compile a lambda expression at runtime to dynamically Select the PropertyName from the Type.
