CODEWITHSUNDEEP
wpfdata-binding
zORg Alex
zORg Alex

Reputation: 381

How to know if binding has no target in case an object doesn't have that property

I have some classes. Some of them has Color Property, but one does not. I'm using same ListBox User Control for them. I want to hide ColorPicker for those classes that have no such property. I know, I can do a workaround and hide it if DataContext is of certain type, but I want to know if there is a way to check if the binding target isn't just null at a moment, but doesn't exist at all.

I used the proposed converter (returning true/false) with no result, but @mm8 proposal to set FallbackValue to false worked well.

Upvotes: 2

Views: 649

Answers (2)

mm8
mm8

Reputation: 169330

You could specify a FallbackValue for a specific binding that the target property will be set the when the source property is not found: https://msdn.microsoft.com/en-us/library/system.windows.data.bindingbase.fallbackvalue(v=vs.110).aspx

Upvotes: 2

heltonbiker
heltonbiker

Reputation: 27605

Use a ValueConverter for the binding, and in the Convert method, check for UnsetValue:

<FrameworkElement Property="{Binding SomeProperty, Converter={StaticResource BindingExists}/>

and

public class BindingExists : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == DependencyProperty.UnsetValue)
        {
            // perhaps do something
            return Binding.DoNothing;
        }
        else if (value == null)
        {
            // perhaps do something else
        }

        return value
    }

    // ...

You can then use DataTriggers to display different templates or whatever, in case of null vs. non-existent value.

Upvotes: 1

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