DataTrigger

<ListBox>
    <ListBox.Triggers>
        <DataTrigger Binding="{Binding IsListBoxEnabled}" Value="False">
            ...
        </DataTrigger>
    </ListBox.Triggers>
</ListBox>

If you try to add a DataTrigger to the ListBox.Triggers Collection, you will get the following 

exception:

 Triggers collection members must be of type EventTrigger.

Fortunately, there is a simple workaround to allow DataTriggers: using Style.Triggers! 

<ListBox ItemsSource="{Binding KeyFrames}" >
    <ListBox.Style>
        <Style>
            <Style.Triggers>
                <DataTrigger Binding="{Binding IsListBoxEnabled}" Value="False">
                    <DataTrigger.EnterActions>
                        <BeginStoryboard>
                            <Storyboard>
                                <DoubleAnimation To="0.3" 

Storyboard.TargetProperty="Opacity" Duration="0:0:0.400"/>
                            </Storyboard>
                        </BeginStoryboard>
                    </DataTrigger.EnterActions>
                    <DataTrigger.ExitActions>
                        <BeginStoryboard>
                            <Storyboard>
                                <DoubleAnimation To="1" 

Storyboard.TargetProperty="Opacity" Duration="0:0:0.400"/>
                            </Storyboard>
                        </BeginStoryboard>
                    </DataTrigger.ExitActions>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </ListBox.Style>
</ListBox>