> Am 14.11.2017 um 11:01 schrieb David Chisnall <[email protected]>:
>
> On 13 Nov 2017, at 19:58, Wolfgang Lux <[email protected]> wrote:
>>
>>> Am 13.11.2017 um 19:13 schrieb David Chisnall <[email protected]>:
>>>
>>>> On 13 Nov 2017, at 17:52, Wolfgang Lux <[email protected]> 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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