You can force validation on an object that uses data annotations. I have an
extension method I use:
public static class ValidationExtensions
{
public static bool TryValidate(this object subject, out ValidationResult
result)
{
var context = new ValidationContext(subject, serviceProvider: null,
items: null);
var results = new List<ValidationResult>();
if (Validator.TryValidateObject(subject, context, results,
validateAllProperties: true))
{
result = null;
return true;
}
result = results.First();
return false;
}
}
... which I call like this:
ValidationResult result;
if (!foo.TryValidate(out result)) return result;
You could conceivably turn that into a simple Boolean property on your object
(“IsValid”) and bind your save button etc to that.
I’d probably wrap the whole thing in a ViewModel. Something like:
public class EditorViewModel<T>
{
public T Subject { get; set; }
public bool IsValid { get { ... } }
}
In fact, if you had a ViewModel you could have public properties that intercept
the underlying subject’s properties and set an “IsDirty” property whenever they
changed. That would address your second question.
Matt
From: Greg Keogh
Sent: Wednesday, December 21, 2011 9:53 AM
To: 'ozWPF'
Subject: Binding validation techniques
Folks, I am binding the properties of an EF4 created entity to a screen full of
controls in the usual way. The default validation behaviour is acceptable for
now, as exceptions from the setters or my validators put a red border around
the guilty controls.
I have other controls like an error icon and the Save button which I’d like to
bind to the validity and consistency of the *whole* entity. Is there some
plumbing in place that can I use to bind controls to the overall state of the
entity? For example, the Save button is disabled if there are 1 or more
property errors.
Another thing I have to consider is giving an indication in the UI of any
controls that have had their values changed. I’m wondering if there is a simple
way of making controls automatically change colour when their value becomes
changed/dirtied via binding. (Changing control colours is not normally a polite
thing to do in the UI, but it would be okay for my demo).
Cheers,
Greg
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