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Editorial Team
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Asked: 2026-05-30T10:05:38+00:00

<Style TargetType=controls:EventTimeView> <Style.Triggers> <Trigger Property=PositioningMethod Value=Column > <Setter Property=Background Value=Black /> </Trigger> </Style.Triggers> </Style>

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<Style TargetType="controls:EventTimeView">      
    <Style.Triggers>         
        <Trigger Property="PositioningMethod" Value="Column" >
            <Setter Property="Background" Value="Black" />
        </Trigger>
    </Style.Triggers>
</Style>

PositioningMethod is a dependency property of EventTimeView of an enum type.

Results in:

System.InvalidOperationException occurred
Message=Property can not be null on Trigger.
Source=PresentationFramework
StackTrace:
   at System.Windows.StyleHelper.UpdateTables(PropertyValue& propertyValue, FrugalStructList`1& childRecordFromChildIndex, FrugalStructList`1& triggerSourceRecordFromChildIndex, FrugalStructList`1& resourceDependents, HybridDictionary& dataTriggerRecordFromBinding, HybridDictionary childIndexFromChildName, Boolean& hasInstanceValues)
InnerException:

I have no idea what might be wrong. The exception is too vague: which property? what is null?

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1 Answer

  1. Editorial Team

    Double check your DependencyProperty definition for PositioningMethodProperty – make sure the owning type is in fact the class in which the DP is defined.

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