I’m using a third party c library that requires registering a callback which
gets called if the operation encounters an invalid server certificate (should i
accept or reject the cert). The callback needs to return yes or no, which I
need to get via a UI prompt so the prompt needs to block so I can return
appropriately from the callback. So my initial thoughts are “present the cert
in a modal window”. So I put the cert in a SFCertificateView in a scroll view
and present it in a modal window but it could not be scrolled up and down which
was the initial problem. I also tried the SFCertificatePanel with the same
problem. After testing I found I couldn’t scroll any scroll view so I knocked
up that small bit of code to show as an example. I tried using
performSelectorOnMainThread and waiting until completion and this funnily
enough works fine in terms of absolutely no UI weirdness but I can’t get a
return value from that plus there were other issues.
There could be any number of operations running concurrently and any one could
require validation at any time.
The callback is basically structured like this
__block BOOL accept;
if ([NSThread isMainThread]) {
accept = [[Controller sharedController] shouldIAccept:certInfo];
}
else {
dispatch_sync(dispatch_get_main_queue(), ^{
accept = [[Controller sharedController]
shouldIAccept:certInfo];
// This is where UI starts playing up when the
controller shows the cert
});
}
return accept;
So the shouldIAccept method needs to block hence runModal. I also just threw
the window up and created my own modal loop but same problem.
On 5 Sep 2014, at 19:59, Jens Alfke <j...@mooseyard.com> wrote:
>
>> On Sep 5, 2014, at 11:44 AM, Jonathan Guy <jonathan...@mac.com> wrote:
>>
>> when the NSOpenPanel opens all kinds of weirdness is going on. The scroll
>> views scroll very erratically if at all and the directories don't list
>> properly.
>
> Well, you've blocked one of the threads that services the global dispatch
> queue — it's stuck in a dispatch_sync call that won't return until the user
> dismisses the open panel. I don't know exactly what kinds of problems
> blocking the queue will cause, but it's definitely not a good idea. (The
> problems you report sound more severe than what I would guess would happen,
> but I definitely don't know how concurrent dispatch queues are implemented.)
>
> You should rewrite your code to use dispatch_async instead. Then when the
> modal session completes, call back to the global dispatch queue to finish
> running your code.
>
> (And the whole scenario you're giving sounds like bad UI design — your code
> shouldn't suddenly pop up a modal panel just because you "need a file from
> the user". The user should be in control of tasks like opening files. But you
> may have created an unrealistic scenario just as an example…)
>
> —Jens
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