How to determine if an user has entered an incorrect input?

Question

I was looking this site for data validation:

http://codeblitz.wordpress.com/2009/05/08/wpf-validation-made-easy-with-idataerrorinfo/

And it sounds great the validation. But for example I realized you can only validate data when the input is correct, if there's a way to set a message when the input is not correct.

I.E. If I have a property Age where is an int, I want to custom the error message to display where the user wrote "a" in a textBox.

I mean, Age property must validate two things, the input will be correct and the range.

Answer 1

Assuming you are using Data-Binding, you need to validate your input with validation rules:

<TextBox Name="tb_act_name"
                         Style="{StaticResource formTextBox}"
                         Validation.ErrorTemplate="{StaticResource validationTemplate}">
                  <TextBox.Text>
                    <Binding Path="act_name"
                             Mode="TwoWay"
                             UpdateSourceTrigger="PropertyChanged"
                             ValidatesOnDataErrors="True">
                      <Binding.ValidationRules>
                        <local:fieldNullOrEmpty ErrorMessage="Enter Client Name" />
                      </Binding.ValidationRules>
                    </Binding>
                  </TextBox.Text>
                </TextBox>

You would simply add more rules in the Binding.ValidationRules section. This is quite a big subject so you may wish to check out MSDN WPF Validation for more help.

Hope this points you in the right direction.

Answer 2

You can try Karl Shifflett's approach

Or you can also add (look at WPF Validation for the whole form):

<TextBox.Text>
 <Binding Path="Age" ValidatesOnDataErrors="True">
  <Binding.ValidationRules>
    <rules:NumericRule />
  </Binding.ValidationRules>
</Binding>
</TextBox.Text>