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Re: issue with auto-enable of Menus


From: Wolfgang Lux
Subject: Re: issue with auto-enable of Menus
Date: Tue, 14 Nov 2017 22:19:07 +0100


> Am 14.11.2017 um 11:01 schrieb David Chisnall <address@hidden>:
> 
> On 13 Nov 2017, at 19:58, Wolfgang Lux <address@hidden> wrote:
>> 
>>> Am 13.11.2017 um 19:13 schrieb David Chisnall <address@hidden>:
>>> 
>>>> On 13 Nov 2017, at 17:52, Wolfgang Lux <address@hidden> wrote:
>>>> 
>>>>> Would it make sense to not have custom code to enable/disable menu items, 
>>>>> and just have appkit do it for you depending on the target?
>>>> 
>>>> In my experience, custom code is unavoidable in almost any non-trivial 
>>>> case because the AppKit is not able to determine exactly when a menu item 
>>>> is applicable and when not. Having support for the selectors is a 
>>>> necessary but not a sufficient condition.
>>> 
>>> IOKit improves this relative to AppKit by adding the delegates to the 
>>> responder chain. For custom views, I’ve taken to doing this and forwarding 
>>> some of the responder chain queries to the delegate.  It would also be nice 
>>> if there were some convention such as {selector}IsEnabled, so if you 
>>> implement -paste: and -pasteIsEnabled then you can turn off paste by 
>>> returning NO to -pasteIsEnabled.
>> 
>> Well, that almost exists in the form of -validateMenuItem: and 
>> -validateUserInterfaceItem:. It’s just that you implement just a single 
>> method that receives a selector argument rather than an individual method 
>> for each selector.
> 
> Yup, and whenever I write one of these I end up with a horrible blob of if 
> statements.  In a language with dynamic dispatch, it would be nice for the 
> menu item to just do NSSelectorFromString once, get the method that 
> dynamically [de]activates it, and call that. We’re already doing a bunch of 
> message sends to deliver things down the responder chain, one more wouldn’t 
> have visible overhead.

So next time you probably should define your validateMenuItem: like this 
(beware, untested code):

- (BOOL) validateMenuItem: (SEL)aSelector
{
  aSelector = NSSelectorFromString([NSStringFromSelector(aSelector) 
stringByAppendingString: @"IsEnabled"]);
  if ([self respondsToSelector: aSelector])
    return (BOOL)[self performSelector: aSelector];
  return YES;
}

And then you can implement -pasteIsEnabled, -copyIsEnabled, etc. as you like. 
:-)

Wolfgang




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