How do I trigger a Maui DataTrigger on load - .net-core

Question

I have a DataTrigger to set some styling based on the result of a validation (it is linked to a TextValidationBehaviour). It works fine, except I want it to trigger when the page loads so the user can see what they need to fill in (i.e. Entry is red until the user types something into it).
So is there any way to trigger the validation on page load?
Here is my code, but open to suggestions:
<Frame WidthRequest="350">
<StackLayout Orientation="Horizontal">
<Entry Style="{StaticResource Key=EntryInverted}" Placeholder="Last Name" Text="{Binding LastName}">
<Entry.Behaviors>
<toolkit:TextValidationBehavior x:Name="LastNameVal"
InvalidStyle="{StaticResource InvalidEntryStyle}"
Flags="ValidateOnValueChanged"
MinimumLength="2"
MaximumLength="99" />
</Entry.Behaviors>
</Entry>
</StackLayout>
<Frame.Style>
<Style TargetType="Frame" BasedOn="{StaticResource Key=EntryFrame}">
<Setter Property="BorderColor" Value="White"/>
<Style.Triggers>
<DataTrigger TargetType="Frame" Binding="{Binding Source={x:Reference LastNameVal}, Path=IsNotValid}" Value="True">
<Setter Property="BorderColor" Value="{StaticResource FrameErrorBorder}" />
</DataTrigger>
</Style.Triggers>
</Style>
</Frame.Style>
</Frame>

Answer 1

You can add a trigger to the entry, such as:
<Entry >
<Entry.Triggers>
<MultiTrigger TargetType="Entry">
<MultiTrigger.Conditions>
<PropertyCondition Property="IsFocused" Value="false"/>
<PropertyCondition Property="Text" Value="{x:Null}"/>
</MultiTrigger.Conditions>
<Setter Property="BackgroundColor" Value="Red"/>
</MultiTrigger>
</Entry.Triggers>
</Entry>
The codes above will make the entry's background color show as red. And it will show the default background color when user taps the entry.
Or you want to the entry is red if the entry has no text in it. You can try the following code:
<Entry >
<Entry.Triggers>
<MultiTrigger TargetType="Entry">
<MultiTrigger.Conditions>
<BindingCondition Binding="{Binding Source={RelativeSource Self}, Path= Text.Length}" Value="0"/>
</MultiTrigger.Conditions>
<Setter Property="BackgroundColor" Value="Red"/>
</MultiTrigger>
<Trigger TargetType="Entry" Property="Text" Value="{x:Null}">
<Setter Property="BackgroundColor" Value="Red"/>
</Trigger>
</Entry.Triggers>
</Entry>
When you use the trigger above, the entry will be red until it has been typed something.