How do I handle DependencyProperty overflow situations?

Question

I have a UserControl and an int DependencyProperty called Value. This is bound to a text input on the UserControl.

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Answer 1

A int property can never be set to something else than an int value. The type of the Text property of a TextBox is however string and the error occurs when when the runtime is trying to set your int property to a string value that doesn't represent a valid integer.

Your dependency property cannot do much about this as it never gets set. As @@Ed Plunkett suggests in his comment you could use a ValidationRule to do something before the value conversion occurs and present an error message to the user if the conversion fails:

public class StringToIntValidationRule : ValidationRule
{
    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        int i;
        if (int.TryParse(value.ToString(), out i))
            return new ValidationResult(true, null);

        return new ValidationResult(false, "Please enter a valid integer value.");
    }
}

---

<TextBox>
    <TextBox.Text>
        <Binding Path="Value" UpdateSourceTrigger="PropertyChanged">
            <Binding.ValidationRules>
                <local:StringToIntValidationRule ValidationStep="RawProposedValue"/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

Please refer to the following blog post about data validation in WPF for more information: https://blog.magnusmontin.net/2013/08/26/data-validation-in-wpf/