Just do the calculation within a dispatch_async within computeSimething.
On Mar 14, 2016, at 4:17 AM, Gerriet M. Denkmann wrote:
>
>> On 14 Mar 2016, at 14:17, Quincey Morris
>> <quinceymor...@rivergatesoftware.com> wrote:
>>
>> On Mar 13, 2016, at 23:50 , Gerriet M. Denkmann <gerr...@mdenkmann.de> wrote:
>>>
>>> - (void)computeSomething
>>> {
>>> self.message1 = @“Start computing”;
>>> // some seconds of computations
>>> self.message1 = @“Result = 42”;
>>> }
>>
>> Assume, conceptually, that drawing only takes place asynchronously (that is
>> to say, setting a new value on the string invokes setNeedsDisplay, that’s
>> all), and it’s obvious why this isn’t going to work.
>>
>> But the real issue is not that the text field won’t update, it’s that you’re
>> blocking the main thread with computation. You should move the computation
>> off the main thread — using dispatch_async to a default queue. At the end of
>> the computation, go back to the main thread (dispatch_async again,
>> specifying the main queue this time) and put the result in the text field.
>>
>> This is, of course, going to introduce threading issues into your design. If
>> the background thread keeps its results private (within the thread) until
>> you switch back to the main thread, you can actually update any permanent
>> data structures on the main thread, avoiding the need for locks or other
>> synchronization techniques. However, you have to arrange for the main thread
>> to avoid trying to use the results before the background computation is
>> done, or to start any new computations, until the old ones are done, as far
>> as such safety checks are necessary for your app.
>>
>> (You can use NSOperationQueue instead of GCD, but I don’t see a lot of
>> advantage in that. The consequences are the same.)
>
> You are absolutely right that a background would be the right thing.
> But this is just a small tool for testing, and it will not take more than a
> few seconds, so I am trying to avoid this.
>
> But I have found a solution (you mentioning setNeedsDisplay was a great help):
>
> - (void)computeSomething
> {
> self.textField1.stringValue = @“Start computing”;
> [self.textField1 display];
> // some seconds of computations
> self.textField1.stringValue = @“Result = 42”;
> }
>
> Gerriet.
>
>
>
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