My view-model exposes a list called MyList
that may be empty or null
. I have an element that I would like hide based on this state. If MyList
is empty or null
, then the element should be collapsed. If it has elements then it should be shown.
Here is my DataTrigger
:
<DataTrigger Binding="{Binding MyList.Count, FallbackValue=0}" Value="0">
<Setter Property="Visibility" Value="Collapsed"></Setter>
</DataTrigger>
DataTrigger
when MyList
is null
? FallbackValue
or will it fail? The FallbackValue
is used if the binding source path does not resolve, if the converter fails, or if the value is not valid for the property's type.
It will not be used if null
is returned, unless null
is not valid for the property type. In this case the DataTrigger
will not be triggered. You can use TargetNullValue
for this case.
<DataTrigger Binding="{Binding MyList.Count, FallbackValue=0, TargetNullValue=0}" Value="0">
<Setter Property="Visibility" Value="Collapsed"></Setter>
</DataTrigger>