I have a problem with an app where I implemented an NSOperationQueue.
It seems that pressing the close button of the iPad makes the UI freeze. The app itself is still running in the background, the UI is updated, it's just that it won't answer to touches or rotation anymore and it doesn't get closed as it should be.
I have an update module that downloads quite a long list of xml files and saves them on the device. The operation queue has a MaxConcurentOperations value of 2.
Usually everything works fine, the app runs fine and dandy, responding to my touches and rotation UNTIL I press the device's button. After this, the UI simply freezes. The progress is still updated (an UILabel), recurrent animations are still displayed, but the app is not closed until all the operations are done.
I'm not calling waitUntilAllOperationsAreFinished on my queue so I don't know what might be causing this.. So far, I've only made tests on a first generation iPad, with iOs 5.0
If anyone can provide me with some tips, I'll really appreciate it. If necessary, I can post the NSOperationQueue and NSOperation class codes, but somehow I have the feeling this about me approaching this wrongly, and not about a faulty line of code
[edit]
I also use a timer to periodically check on the download status, but I noticed that not calling the timer doesn't eliminate the problem
self.timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:#selector(xmlDownloaded) userInfo:nil repeats:YES];
[edit2]
After some further research, I made sure that my operations are concurrent and just to be sure, I changed the way I added my operations to the queue.
Instead of
[downloadQueue addOperation:op];
I added them to a mutable array called "operations" and in the end I used
[downloadQueue addOperations:operations waitUntilFinished:NO];
but my app still freezes when I press the close button...
Wild guess, you are locking the main thread waiting for your operation to complete / you are destroying your operation delegate on viewWillDisappear?
It seems there was another function causing this, even though I don't understand why...
I had a label animation
CABasicAnimation *fadey = [CABasicAnimation animationWithKeyPath:#"opacity"];
[fadey setToValue:[NSNumber numberWithFloat:0.35f]];
fadey.repeatCount = HUGE_VALF;
[fadey setAutoreverses:YES];
[fadey setDuration:0.6f];
This small function was causing the app to wait until all the operations were finished in order to close the app. The weird part is that the function was not even called in with the NSOperations, but before them
Again, I have no idea why... everything breaks when I press the close button, otherwise there are no problem. So if anyone else runs into a similar issue, it might help to check for some repeating animations
Related
NOTE: Updated below...
I have a cocoa desktop application which consists of a series of controls around a custom NSView. I am using displayLink to drive the updates.
When a user clicks on an NSControl (a slider, a button, a checkbox, a radio button) the application appears to freeze until the mouse is released. I can confirm in fact that the displayLink callback (getFrameForTime) is NOT firing during the time. If I create a timer, that also does not fire, both remain paused until the user releases the mouse, at which point the application resumes updating.
The control is bound, and if I update that value from another thread (for example, via a callback from a MIDI interface) the slider behaves as expected: it moves, the value updates and the application does not pause.
I feel like this should be a fairly obvious fix, but I'm stumped.
Checking "continuous" in IB does as advertised: sends the values continuously, but still exhibits this behavior (preventing the UI update) until the mouse is released.
This seems to be related specifically to mouseDown on NSControl? Why would this block, and do I really need to subclass all my UI elements to change this behavior (seems extreme)
DisplayLink is in its own thread, so why mouseDown on the main thread block it? If this is the case, given the injunction on updating the Cocoa UI from other than the main thread, how do I deal with it?
Any help much appreciated.
Update
Per #Nikolai's comments below, I can confirm that using an NSTimer and adding it to NSEventTrackingRunLoopMode does NOT block. However, I would really like to use CVDisplayLink which (according to the documentation) runs in it's own thread and should not be blocked in this way. Unlike CADisplayLink, I cannot find a way to explicitly assign a runloop to CVDisplayLink (it seems it doesn't work that way), so perhaps the new question should be:
Why does CVDisplayLink block on NSEventTrackingRunLoopMode?
When clicking on an NSControl the runloop mode goes from NSDefaultRunLoopMode to NSEventTrackingRunLoopMode, as long as the mouse is down. That means that only run loop sources (display link) and timers fire that have been added to this mode.
You can add timers to any mode by using -[NSRunLoop addTimer:forMode:]. For a display link the equivalent method is -[CADisplayLink addToRunLoop:forMode:].
To make your animation continue during event tracking you would do something like:
[myDisplayLink addToRunLoop:[NSRunLoop currentRunLoop]
forMode:NSEventTrackingRunLoopMode];
Your test project shows that you are calling a view's display method from within the display link's callback.
When commenting the display message out, the display link is called continuously even while moving the slider.
So what goes wrong is that when the runloop goes into event tracking mode, the call to display on the display link's thread blocks until the mouse is released and the run loop goes back to default mode. You can easily confirm this by putting a log statement before the call and one after it.
Why exactly that happens is not clear to me. What is clear is that it's illegal to call a view's methods from a background thread. You have to trigger the view's display by dispatching a setNeedsDisplay: on the main thread:
static CVReturn MyDisplayLinkCallback(CVDisplayLinkRef displayLink, const CVTimeStamp* now, const CVTimeStamp* outputTime, CVOptionFlags flagsIn, CVOptionFlags* flagsOut, void* displayLinkContext)
{
dispatch_async(dispatch_get_main_queue(), ^{
[(__bridge MyCustomView*)displayLinkContext setNeedsDisplay:YES];
});
return kCVReturnSuccess;
}
I'm trying to figure out a way to have a timer that begins at the time that an app is installed and continues to run even when the app is in the background. I'm basically using the timer to periodically check the battery life of an external device that is linked to the phone. I've been told that the best way to do this is to use some sort of delegate calls to a timer function, but I'm fairly new to IOS and am pretty confused on how to do that. I know how to set up the timer and get the battery life, I'm however perplexed on how to keep the timer going through the life of the app. Any help you could give would be extreeemely appreciated! Thanks a bunch!
Running an app in the background (forever) isn't possible.
But while your app is running... you can set the repeats parameter of the method scheduledTimerWithInterval:target:selector:userInfo:repeats: to YES.
Here's a link to running it in the background for a certain period of time to perform a relatively large task.
run even when the app is in the background
Not possible. You can request an extra 10 minutes, but thats it. You will not be able to write your app as is.
For the timer part of your question, you can do this:
[NSTimer scheduledTimerWithTimeInterval:60.0
target:self
selector:#selector(checkBattery:)
userInfo:nil
repeats:YES];
But you should really be subscribing to the notifications on battery change events. Here is sample code from apple that shows how to do it.
coneybeare is right. This is iOS policy, which is in place exactly to prevent what you are trying to do, i.e. exhaust the iPhone's (or iPad's) battery life.
Im developing an app that has to run in the background. It's a location based app, so it runs all the time, the OS doesn't kill it.
It should send some info every 10 secs(just for debugging), I set a timer once its in the background. I set a breakpoint in the function that should be executed every 10 secs, which is never called, but if I pause the app and then continue the timer is called, and then the timer is executed every 10 secs without problems, weird right?
I thought that the timer would be executing anyway when I wasn't debugging, but it isn't, same thing as if I didn't pause the debugging.
My question is WHY?? The timer is set correctly(I assume) since it works after pausing, but it's not.
Any ideas?
The way I set the timer is:
self.timer = [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:#selector(doStuff) userInfo:nil repeats:YES];
And in the function I connect to a webservice.
Thanks.
I have a similar app design and was stuck on the same thing. What I found somewhere on the internet is adding this type of statement applicationDidEnterBackground:
UIBackgroundTaskIdentifier locationUpdater =[[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
[[UIApplication sharedApplication] endBackgroundTask:locationUpdater];
locationUpdater=UIBackgroundTaskInvalid;
} ];
This tells the os that you still have things going and not to stop it.
I have my timer attached to this function
//this is a wrapper method to fit the required selector signature
- (void)timeIntervalEnded:(NSTimer*)timer {
[self writeToLog:[NSString stringWithFormat:#"Timer Ended On %#",[NSDate date]]];
[self startReadingLocation];
[timer invalidate];
timer=nil;
}
I set the timer in my my location manager delegate methods.
I feel your pain. I found that these things were super finicky. This is what worked for me. I hope it helps. I have found that there isn't any really restrictions in what you can do in the background.
There might be restrictions on what you can do in the background. Try adding the timer to the run loop before going into the background. Even that might not work; it may be that the only code of yours that can run in the background is the code called by the Core Location methods you've signed up for (e.g. locationManager:didUpdate...). But my impression is that timers already running before you start to go into the background will continue to run.
I have encountered a strange bug in my application, and I am trying to debug it using step execution.
However it seems that things on an iphone often do not happen as synchronously as I would like, for example when I step-over this line
[self.view addSubview:FinndomoEmbeddedMWView.view];
nothing happens in the emulator.
If I just let the program run, the view is added and the screen changes as it should.
So I am guessing, addSubview does not do everything related to adding a view, it just sort of starts the process, and then it is completed later.
I don't know if there are message queues on ios similair to winapi, but there must be something like that, so is there a function for "processing all accumulated messages". I would then like to call this function after my addSubview and actually see the things change in the emulator while I debug, not when the program is running.
And I experience this not only with addSubview, so I want to have a general solution for things like this.
Sat yesterday and found out the answer:
NSDate *dtr = [[NSDate alloc] initWithTimeIntervalSinceNow:0.5];
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:dtr];
This is sort of what I wanted. As you can see, this particular code may end up waiting for 0.5 seconds if there are no more events, and if there are events pending, it is only processing the first one and then returns (according to documentation).
But that could be avoided of course, this is just an example, if anyone will want the same thing. In my case there was only 1 important event, and so the provided snippet worked.
The short answer is no.
Cocoa is event-driven.
The core of each app is the event loop. On each pass through the event loop, the app handles events added to the event queue. Updating the screen is one such event.
Thus, changes to screen display don't take place until after your code returns, on the next pass through the event loop.
For debugging purposes where you want to figure out what's happening line-by-line, you need to either use the debugger's facilities, or add NSLog statements to your code.
For some reason when I push down (click and hold) on any control, the NSTimer in my App freezes and does not fire until I release the mouse button. It simply does not fire while I have the mouse pressed. This is fine for short periods, but it also freezes if I have a popup menu open, or a combobox dropped down.
I'm not sure if there is something I missed, but it seems like this is incorrect behavior.
I want to be able to click the down arrow of an NSPopUpButtonCell (or even click and hold an NSTableView) without the entire NSTimer freezing (which redraws an NSView).
Any comments / suggestions would be appreciated.
The NSTimer is added to the currentRunLoop with mode NSDefaultRunLoopMode.
While the mouse is down, the run loop is in the NSEventTrackingRunLoopMode. Therefore, any event that's not received onto the EventTracking event queue won't be serviced until the runloop returns to the appropriate mode.
The way around this is to add the timer to the runloop for both modes (default and event tracking).
Instead of adding two or more timers to different runloops or using multithreading (as you won't then be able to update the UI from another thread) simply add the timer to the NSRunLoopCommonModes:
NSTimer *myTimer = [NSTimer timerWithTimeInterval:RefreshInterval target:self selector:#selector(doWork) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:myTimer forMode:NSRunLoopCommonModes];
Assuming you're just dealing with one thread in your application, what you described is perfectly expected. By default, NSTimer's are added to the current NSRunLoop which, in your case, is also responsible for dealing with UI interaction. When it gets tied up with handling UI interaction, it can't check your timer and "fire" it.
A solution is to use multi-threading so as to avoid this tie-up. Here's a nice blog post on this very subject: http://blog.narent.com/?p=21
EDIT: See Dave's post for an alternative (and more elegant IMO) solution
Also see:
NSTimer doc
NSRunLoop doc
Threading programming guide