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Mac Forum / Programming / Mac Programming / May 2008Forcing an update of an NSTextField?
I've got a code that has an NSTextField that it uses as an error line. It's linked to an outlet variable called 'errorMessage'. In awakeFromNib I've got a line that reads [errorMessage setStringValue:@"Ready."]; which works as expected. However, further into the program I've got lines that read: [errorMessage setStringValue:@"Mounting network share..."]; [self mountNetworkShare]; 'mountNetworkShare' is a routine that mounts an SMB share using FSMountServerVolumeSync, that I guess ties the machine up for a couple of seconds. The problem I'm seeing is that the errorMessage field doesn't get updated before it goes into the routine. I'm guessing it gets updates immediately after, but as I'm setting it back to blank the effect is that the 'Mounting...' message never gets displayed. Is there a way to force it to update the display? Or am I doing something amusingly wrong? Many thanks. Jim  Signaturehttp://www.ursaMinorBeta.co.uk http://twitter.com/GreyAreaUK "Sometimes when I talk to a Windows person about using a Mac, I feel like I'm explaining Van Halen to a horse." Merlin Mann > [errorMessage setStringValue:@"Mounting network share..."]; > [self mountNetworkShare]; [quoted text clipped - 7 lines] > after, but as I'm setting it back to blank the effect is that the > 'Mounting...' message never gets displayed. I should point out that I've also tried adding the lines: [errorMessage setNeedsUpdate]; [errorMessage update]; before the [self mountNetworkShare] line, to no avail. Jim Signaturehttp://www.ursaMinorBeta.co.uk http://twitter.com/GreyAreaUK "Sometimes when I talk to a Windows person about using a Mac, I feel like I'm explaining Van Halen to a horse." Merlin Mann > 'mountNetworkShare' is a routine that mounts an SMB share using > FSMountServerVolumeSync, that I guess ties the machine up for a couple of > seconds. that’s your problem right there. you really can’t do something that’s going to take a couple of seconds in your app’s main thread. your app will appear hung during that time, which is unacceptable. launch a background thread and do your long-running operations there instead. >> 'mountNetworkShare' is a routine that mounts an SMB share using >> FSMountServerVolumeSync, that I guess ties the machine up for a couple of [quoted text clipped - 5 lines] > > launch a background thread and do your long-running operations there instead. Yes, I thought that might be the case. Could you point me to any example code for threads? They're not something I've had to use yet in my very limited Cocoa experience. Many thanks. Jim Signaturehttp://www.ursaMinorBeta.co.uk http://twitter.com/GreyAreaUK "Sometimes when I talk to a Windows person about using a Mac, I feel like I'm explaining Van Halen to a horse." Merlin Mann > >> 'mountNetworkShare' is a routine that mounts an SMB share using > >> FSMountServerVolumeSync, that I guess ties the machine up for a couple of [quoted text clipped - 17 lines] > > Jim - (void)mounterThread:(id)arg { NSAutoreleasePool* p = [[NSAutoreleasePool alloc] init]; [self mountNetworkShare]; [errorMessage performSelectorOnMainThread:@selector(setStringValue:) withObject:@"" waitUntilDone:YES]; [p release]; } ... [errorMessage setStringValue:@"Mounting network share..."]; [NSThread detachNewThreadSelector:@selector(mounterThread:) toTarget:self withObject:nil]; Something like that, anyway. Just typed into MTNW without testing. Signature"Harry?" Ron's voice was a mere whisper. "Do you smell something ... burning?" - Harry Potter and the Odor of the Phoenix > - (void)mounterThread:(id)arg > { [quoted text clipped - 12 lines] > > Something like that, anyway. Just typed into MTNW without testing. Oh, I see. Thanks. Does main thread execution stop until that new thread is complete? I only ask because the commands immediately following [self mountNetworkShare] musn't be executed until it's finished mounting (or at least trying to mount) the share. Is that what the 'waitUntilDone:YES' bit does? Again, thank you. Jim Signaturehttp://www.ursaMinorBeta.co.uk http://twitter.com/GreyAreaUK "Sometimes when I talk to a Windows person about using a Mac, I feel like I'm explaining Van Halen to a horse." Merlin Mann > Does main thread execution stop until that new thread is complete? if it did, there would be no point in launching the thread! > I only ask because the commands immediately following > [self mountNetworkShare] musn't be executed until it's finished > mounting (or at least trying to mount) the share. in that case, you’ll have to arrange for the background thread to send a signal to your foreground thread, letting it know when it can continue doing what it was up to. sending an event that your app responds to would be a good idea. > Is that what the 'waitUntilDone:YES' bit does? nope. >> Does main thread execution stop until that new thread is complete? > > if it did, there would be no point in launching the thread! Heh. Yes, good point. >> I only ask because the commands immediately following >> [self mountNetworkShare] musn't be executed until it's finished [quoted text clipped - 4 lines] > what it was up to. sending an event that your app responds to would be a good > idea. I've started investigating [[NSThread alloc] initWith...] instead. After I've executed [myThread start] I thought I could test to see if it's finished with either [myThread isExecuting] or [myThread isFinished] but I'm getting odd results from those. Probably me just being too hasty. You've certainly given me somethinig to think about, thank you :-) Jim Signaturehttp://www.ursaMinorBeta.co.uk http://twitter.com/GreyAreaUK "Sometimes when I talk to a Windows person about using a Mac, I feel like I'm explaining Van Halen to a horse." Merlin Mann > >> Does main thread execution stop until that new thread is complete? > > [quoted text clipped - 17 lines] > finished with either [myThread isExecuting] or [myThread isFinished] but I'm > getting odd results from those. Probably me just being too hasty. Yeah. Don't do that. Polling is bad. See my other message for ideas on having the thread either trigger or directly perform the follow-up code when it's time. G Signature"Harry?" Ron's voice was a mere whisper. "Do you smell something ... burning?" - Harry Potter and the Odor of the Phoenix > > - (void)mounterThread:(id)arg > > { [quoted text clipped - 16 lines] > > Does main thread execution stop until that new thread is complete? No. That's the point of threads and that's why it fixes your problem with the text field updating. > I only > ask because the commands immediately following [self mountNetworkShare] > musn't be executed until it's finished mounting (or at least trying to > mount) the share. Ah. In that case, you have a few options. The easiest one, although it might not be the best, is to move those lines into the thread method. The most flexible is to perform those follow-up lines in their own method called, say: - (void)mountAttemptFinished:(NSNotification*)n { // Do stuff. } Then at some point before your thread launches register that method as a handler for a notification you've invented, and end the mounterThread: method with code to issue that same notification. You can even pass information along in that notification to signal whether or not the mount succeeded (or just about anything else you might want to communicate). > Is that what the 'waitUntilDone:YES' bit does? No. That prevents the worker thread from continuing until the text field has been blanked (although not necessarily requiring that it refresh to reflect that). Signature"Harry?" Ron's voice was a mere whisper. "Do you smell something ... burning?" - Harry Potter and the Odor of the Phoenix > > I only > > ask because the commands immediately following [self mountNetworkShare] [quoted text clipped - 18 lines] > mount succeeded (or just about anything else you might want to > communicate). Right-o, thanks. > > Is that what the 'waitUntilDone:YES' bit does? > > No. That prevents the worker thread from continuing until the text field > has been blanked (although not necessarily requiring that it refresh to > reflect that). Gotcha. Silly question in hindsight :-) Jim Signature'Cloverfield' in nine words: "What is it?!" "We're gonna die!" BOOM! Roll credits. http://www.ursaminorbeta.co.uk http://twitter.com/greyareauk |
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