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Jean Hominal
Jean Hominal

Reputation: 16796

What are the special values of WPF's Binding engine when converting values?

I already know about the Binding.DoNothing that one can return from an IValueConverter implementation to signify that no other operation should take place.

However, I cannot find a reference, or documentation nicely summing out, what the other special values are - such as returning the fallback value. What are they?

Upvotes: 7

Views: 3691

Answers (1)

Jon
Jon

Reputation: 437664

Binding.DoNothing is an object instance that you actively return from a value converter; it instructs the binding engine to not update the value of the target property at all. Here's a nice example by Josh Smith of what you might use this for.

FallbackValue is a property that you set on bindings; it allows you to specify the value to be applied to the target property if:

  • the binding source cannot be resolved (e.g. wrong binding path), or
  • the binding property value is equal to DependencyProperty.UnsetValue, or
  • a value converter used for the binding throws an exception, or
  • a value converter used for the binding returns DependencyProperty.UnsetValue, or
  • the value produced by the binding pipeline is not valid for the target property (e.g. wrong type)

TargetNullValue is also a property you set on bindings; it allows you to specify the value to be applied to the target property if the value of the source property is null. For example, if you bind a text box to a string property TargetNullValue lets you pick what appears in the text box if the source string is null.

Upvotes: 16

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