Technical Q&A QA1213

HIObjectRegisterSubclass returns paramErr

Q: I called HIObjectRegisterSubclass to register my custom subclass of HIView, and got back paramErr (-50). Why?

A: Assuming all your other parameters are correct, the problem may be that the HIView object class is registered a little too lazily. Ordinarily the class is registered when the first HIView is instantiated. However, if you try to register a subclass of HIView before instantiating any HIViews (any windows or controls), then the HIView class hasn't been registered yet, and HIObjectRegisterSubclass can't find it and returns an error.

This problem (r. 3020648) will be fixed in an upcoming software update; with that fix, HIObjectRegisterSubclass will allow lazily registered classes to register themselves if it can't find the base class already registered.

Until then, you can work around this by creating an instance of some other Apple-defined control, for example a pushbutton that you can create passing NULL as window parameter since you don't need a valid window with the new HIToolbox creation scheme. You can then dispose that control. This instantiation of a known HIView class will ensure that the HIView class itself will be registered and later calls to HIObjectRegisterSubclass will succeed.

[Nov 12 2002]