CODEWITHSUNDEEP
c#wpfxamlbehaviorvalidationrule
Alexander Ventura
Alexander Ventura

Reputation: 1160

ValidationRule vs Behavior in WPF

Say I am trying to implement a piece of functionality in which a text box only allows integers to be inputted in by the user. I can implement this two ways, using a ValidationRule that checks whatever the user inputs and binding it to the text property through the XAML or I can create a new behavior and attach it to the control (not through binding).

Examples of the XAML on both:

Behavior: <TextBox behaviors:DigitsOnlyBehavior.IsDigitOnly="True"/>

ValidationRule which binds to the Window's Text property

<TextBox>
    <TextBox.Text>
        <Binding RelativeSource = "{RelativeSource Mode=FindAncestor, AncestorType=Window}" Path="Text" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay">
            <Binding.ValidationRules>
                <utils:RestrictInputTypeValidator Restriction="IntegersOnly" ValidatesOnTargetUpdated="True"/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

What are the advantages and disadvantages of these approaches? When should I use them? Or is it a matter of preference?

Upvotes: 4

Views: 1425

Answers (1)

denis morozov
denis morozov

Reputation: 6316

With Behaviors I like and expect a "positive" scenario/workflow without errors. The focus is no errors. The user gets pretty quickly that when they type an 'a' in the TextBox with Numeric behavior that it doesn't take it, that it's a numeric textbox, and this is how it works.

With Validation, the focus seems to be more on the error. I can have a Numeric TextBox, but I also don't take numbers beyond 100, if you type '101', I let you know that this is not acceptable. The focus here is to guide user into what is unacceptable by throwing a validation error.

Behavior Advantages:

  • Prevention (you don't let the user shoot themselves in the foot) by entering bad data.
  • Model stays clean. TextBox's Binding doesn't even hit the setter, as the behavior prevents it, hence, no XAML triggered back with PropertChanges, or ValidationErrors, etc.

Behavior Disadvantage:

-could be confusing , so if you put the logic not to accept '101', there is no default way to guide the user.

Upvotes: 0

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