Using binding for the Value property of DataTrigger condition

Question

I'm working on a WPF application and struggling with a data trigger. I'd like to bind the value of the trigger condition to some object I have:

<DataTrigger Binding="{Binding Foo}" 
             Value="{Binding ElementName=AnotherElement, Path=Bar}">..

However, I'm not allowed as it doesn't seem to be possible to use bindings for the Value property. Is it? Can I achieve this somehow? I get the following error:

A 'Binding' cannot be set on the 'Value' property of type 'DataTrigger'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject.

Answer 1

No, it is not possible. As the error message says, only dependency properties can be targets of WPF bindings, and DataTrigger.Value is not a dependency property. So you will need to assign an actual value.

The workaround is to use a MultiBinding whose child Bindings are the two bindings you want to compare, with an IMultiValueConverter which returns true if the two inputs are equal and false if they are unequal. The DataTrigger can then use that MultiBinding, and a Value of True.

Answer 2

I have the same problem and I don't understand the solution of 'itowlson', can someone explain it ?