When the field is created on a Page, why don't you use:
public MyPage(PageParameters p)
{
TextField tf = new TextField("", foo, "");
tf.add(new FValidateAttribModifier(tf));
add(tf);
}I suppose when you want to have a special kind of field, like a social security number field, you'd want to extend TextField, but even then you can extend HTMLComponent, delegate all behaviour to TextField (which is very simple when using Eclipse), and put in your own behaviour.
It's a basic OO principle to "favor composition over inheritance" (use google on that :o)). In this case, you aren't creating an actual new kind of text field, but are adding some behaviour to the text field which can already be done using the public interface.
I'd use a Factory (Method) for this kind of behaviour rather than inheritance.
Martijn
Eelco Hillenius wrote:
Just look at the code, e.g. DataTextField. That's code duplication. It would be possible to wrap the textfield class/ use delegation but that would mean much more code, and also that class not being a 'TextField' because it would inherit from e.g. HTMLComponent directly.
All I want to do is stuff like:
class FValidateTextField extends TextField
{
public FValidateTextField(String name, Serializable object, String expression)
{
super(name, object, expression);
add(new FValidateAttribModifier(this));
}
}
There's nothing wrong with wanting to do that, is there? I mean, by adding such a modifier to instances I really introduce new behaviour which thus satisfies the inheritance requirement of behaviour, but it is still a text field that uses the normal text field rendering behaviour.
Eelco
Martijn Dashorst wrote:
And this is not possible using delegation? Or would that be too much effort on the developers part?
Martijn
Eelco Hillenius wrote:
When working on the contrib section, it's quite irritating that most form component implementations (like TextField etc) are final. What I would like to do a lot (and think other users might as well) is just override such a class and provide a custom constructor that adds eg some attribute modifiers or validators. I also think this would be quite a common use case for users that want to implement their componany std's components etc.
I would like to propose to make the form components non-final *but* finalize all important methods that have component specific implementations (like handleComponentTag or handleBody) final.
Any objects/ what's your vote?
Eelco
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