Change Dependency Property value on Textbox ValidationRule - wpf

Question

I have implemented Custom Control inheriting from ContentControl,which has dependency property called "CanNavigate"(bool).
In a Window.xaml,I have a text box with some ValidationRule checking for Textbox emptiness.I want to set "CanNavigate" to true/false based on TextBox.Validation.HasError as shown below code:
<Style TargetType="{x:Type TextBox}">
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip"
Value="{Binding RelativeSource={RelativeSource Self},
Path=(Validation.Errors)[0].ErrorContent}"/>
<Setter Property="{Binding CanNavigate}" Value="false"></Setter>
</Trigger>
</Style.Triggers>
</Style>
Having this code,gives an error "'Property' property cannot use markup extensions or property element syntax on Setter. Only the Value property can use markup extensions or property element syntax. Error at object 'System.Windows.Setter' in markup file"
Is there a way where I can set CanNavigate property based on TextBox.validationError.
Regards,
Patil

Answer 1

Concerning your first setter I think you should replace this setter with a Binding on the ToolTip property and use a ValueConverter when neccessary, triggers can not.
It's better to do it like this (note I haven't tested this piece of code I'm just trying to point to this way):
<TextBox ... ToolTip="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}" />
Concerning the second setter: In a setter when defining the Property you don't need to specify a Binding you just provide the property name just like this:
<Setter Property="CanNavigate" Value="False" />