R – WPF databinding and converters

converterdata-bindingwpf

I'm trying to databind to a listbox like so:

<ListBox x:Name="MyListBox" Margin="0,0,0,65">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Converter={StaticResource MyConverter}}" />
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

The reason I am binding to the whole object and not a property is because my converter will need multiple properties of the object to build the string that it returns.

This works and my string is returned. But then when I change the ObservableCollection that this is based on the value doesn't change on the screen. If I bind to just a single property and change it, then the value does change.

What can I do differently? I can't bind to a single property since I need the entire object in the converter… And the ConverterParameter is already being used.

Best Answer

Remember, if you bind to the "main" property and the value of the main property itself isn't changed, the binding will have no reason to refresh itself. It has no clue that your converter is actually based off of a sub-property. What you can do is use a MultiBinding where you bind not only the "main" property, but also a specific sub-property. This gives your IMultiValueConverter implementation access to the main data object, but because you're also binding to the sub-property that's changing, will also be refreshed when that sub-property's value changes.

Related Solutions

.net – How to use WPF bindings with RelativeSource

If you want to bind to another property on the object:

{Binding Path=PathToProperty, RelativeSource={RelativeSource Self}}

If you want to get a property on an ancestor:

{Binding Path=PathToProperty,
    RelativeSource={RelativeSource AncestorType={x:Type typeOfAncestor}}}

If you want to get a property on the templated parent (so you can do 2 way bindings in a ControlTemplate)

{Binding Path=PathToProperty, RelativeSource={RelativeSource TemplatedParent}}

or, shorter (this only works for OneWay bindings):

{TemplateBinding Path=PathToProperty}

C# – WPF Data Binding and IValueConverter

You can also use a MultiBinding.. Bind to the Person object, the FirstName and LastName. That way, the value gets updated as soon as FirstName or LastName throws the property changed event.

<MultiBinding Converter="{IMultiValueConverter goes here..}">
    <Binding />
    <Binding Path="FirstName" />
    <Binding Path="LastName" />
</MultiBinding>

Or if you only use the FirstName and LastName, strip the Person object from the binding to something like this:

<MultiBinding Converter="{IMultiValueConverter goes here..}">
    <Binding Path="FirstName" />
    <Binding Path="LastName" />
</MultiBinding>

And the MultiValueConverter looks like this:

class PersonNameConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
            return values[0].ToString() + " " + values[1].ToString();
    }

    public object ConvertBack(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
            throw new NotImplementedException();
    }
}

But of course, the selected answer works as well, but a MultiBinding works more elegantly...

Best Answer

Related Solutions

.net – How to use WPF bindings with RelativeSource

C# – WPF Data Binding and IValueConverter

Related Topic