Is there any method (like – viewDidLoad) to continuously execute a part of code? I need to be able to check a value on a remote server continuously.
The way you would do this is to set up an NSTimer.
-(void)startCheckingValue
{
mainTimer = [NSTimer timerWithTimeInterval:1.0 target:self selector:#selector(checkValue:) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:mainTimer forMode:NSDefaultRunLoopMode];
}
-(void)checkValue:(NSTimer *)mainTimer
{
//Placeholder Function, this is where you write the code to check your value on the remote server
}
The timerWithTimeInterval function is the one that you are interested in, the main things that you need to pass it, as you see above, are the interval at which it will execute the function whose selector you pass it. The time interval is in seconds, so it is currently set to check every second, which is probably way too fast.
Use an NSTimer to execute the same block of code every x seconds. However, I don't think that's what you want, given that it would put a lot of extra load on the server and you might get banned, so there's probably a better way.
apple's page on NSTimer use
You ned to use NSTimer For this:
in your interface declare a NSTimer object like:
NSTimer *timer;
in your .m viewDidLoad method add the below line.
timer = [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:#selector(timerFireMethod:) userInfo:nil repeats:YES];
In the timerFireMethod method you need to do the server calling and other stuffs.
Related
I cannot seem to work this one out. Here is my set up:
I have a function called requestDataWithCompletion:(someBlock)block. I call it when the class is initialised. The function requests certain motion data. I want to do this periodically, therefore, the first time I call this function, I specify some completion code which sets up a timer that re-calls this function periodically. The timer calls it via another function requestDataWithoutCompletion which simply calls the requestDataWithCompletion but with an empty block (so I don't keep creating timers);
- (void) requestDataWithCompletion:(someBlock)block {
// BREAK POINT 1
[self.motionManager queryActivityStartingFromDate:start toDate:[NSDate date] toQueue:self.queue withHandler:^(NSArray *activities, NSError *error) {
// BREAK POINT 2
// do some processing;
block();
}];
}
The block simply creates a timer on the main queue, which periodically recalls this function, but with no completion (since I don't want to keep creating more timers).
block = ^{
dispatch_async(dispatch_get_main_queue(), ^{
self.timer = [NSTimer scheduledTimerWithTimeInterval:timerInterval
target:self selector:#selector(requestDataWithoutCompletion) userInfo:nil repeats:YES];
});
}
- (void) requestDataWithoutCompletion {
[self requestDataWithCompletion^{;}];
}
The amazing thing is that despite this set up, my app is creating timer after timer! I can't understand why.
I have placed break points in requestDataWithCompletion method. One is outside the block submitted to NSOperationQueue to get activity data (BREAKPOINT 1) and one is inside the block submitted to NSOperationQueue. (BREAKPOINT 2). Basically it shows that each time the method is called by the timer, BREAKPOINT 1 has an empty completion block (as it should be) but then strangely BREAKPOINT 2 has the completion block I submitted when I first called the function when initialising the class. Therefore, it continues to create a new timer each time the function is called by the timer. Over time, this means a massive number of timers and then the app crashes!
I have a feeling this is something to do with NSOperationQueue, but I really don't know what it could be.
In your initialisation (or when you first want to get the data and then continue getting it):
self.timer = [NSTimer scheduledTimerWithTimeInterval:timerInterval target:self selector:#selector(requestDataWithoutCompletion) userInfo:nil repeats:YES];
[self.timer fire]; //get the activity data immediately.
- (void) requestDataWithoutCompletion {
[self requestDataWithCompletion:^{}];
}
With your original requestDataWithCompletion: method. (though you could get rid of requestDataWithCompletion: and put it's code directly in requestDataWithoutCompletion if you're not using it elsewhere)
I have surfed on a bunch of resources from the internet but still couldn't get any idea of what I'm trying to implement.
I would like to record user preferences by detecting how much time they have stayed in each information pages.
In order to make this question simpler, that says I have a entrance page with 5 different theme pages which represent different information.
I would like to know which page is the page that user most interesting.
What I wish to do is to put a counter in each theme pages and calculate how much time they stay in that page (the counter should be able to pause for reentrance), and then when I press a button on the entrance page, an alert will tell me which page is the page that user spent most of time on it.
I hope this make sense!
Does anyone have any experience on this? I would be most appreciative if anyone can provide some codes and examples for me.
ViewController A:
- (void)viewDidLoad {
[super viewDidLoad];
//create iVar of NSInteger *seconds
seconds = 0;
NSTimer *timer = [NSTimer timerWithTimeInterval:1.0 target:self selector:#selector(increaseTimeCount) userInfo:nil repeats:YES];
[timer fire];
}
- (void)increaseTimeCount {
seconds++;
}
- (void)dealloc {
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
// you can add to array too , if you want and get average of all values later
[defaults setInteger:seconds forKey: NSStringFromClass(self)];
}
now in Entrance View ..
get the time as
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSInteger *secondsInView = [defaults integerForKey:NSStringFromClass(View1ClassName)];
Firstly I'd like to draw your attention to the Cocoa/CF documentation (which is always a great first port of call). The Apple docs have a section at the top of each reference article called "Companion Guides", which lists guides for the topic being documented (if any exist). For example, with NSTimer, the documentation lists two companion guides:
Timer Programming Topics for Cocoa
Threading Programming Guide
For your situation, the Timer Programming Topics article is likely to be the most useful, whilst threading topics are related but not the most directly related to the class being documented. If you take a look at the Timer Programming Topics article, it's divided into two parts:
Timers
Using Timers
For articles that take this format, there is often an overview of the class and what it's used for, and then some sample code on how to use it, in this case in the "Using Timers" section. There are sections on "Creating and Scheduling a Timer", "Stopping a Timer" and "Memory Management".There are a couple of ways of using a timer. From the article, creating a scheduled, non-repeating timer can be done something like this:
1) scheduled timer & using selector
NSTimer *t = [NSTimer scheduledTimerWithTimeInterval: 2.0
target: self
selector:#selector(onTick:)
userInfo: nil repeats:NO];
if you set repeats to NO, the timer will wait 2 seconds before
running the selector and after that it will stop;
if repeat: YES, the timer will start immediatelly and will repeat
calling the selector every 2 seconds;
to stop the timer you call the timer's -invalidate method: [t
invalidate]; As a side note, instead of using a timer that doesn't
repeat and calls the selector after a specified interval, you could
use a simple statement like this:
[self performSelector:#selector(onTick:) withObject:nil afterDelay:2.0];
this will have the same effect as the sample code above; but if you want to call the selector every nth time, you use the timer with repeats:YES;
2) self-scheduled timer
NSDate *d = [NSDate dateWithTimeIntervalSinceNow: 60.0];
NSTimer *t = [[NSTimer alloc] initWithFireDate: d
interval: 1
target: self
selector:#selector(onTick:)
userInfo:nil repeats:YES];
NSRunLoop *runner = [NSRunLoop currentRunLoop];
[runner addTimer:t forMode: NSDefaultRunLoopMode];
[t release];
this will create a timer that will start itself on a custom date
specified by you (in this case, after a minute), and repeats itself
every one second
3) unscheduled timer & using invocation
NSMethodSignature *sgn = [self methodSignatureForSelector:#selector(onTick:)];
NSInvocation *inv = [NSInvocation invocationWithMethodSignature: sgn];
[inv setTarget: self];
[inv setSelector:#selector(onTick:)];
NSTimer *t = [NSTimer timerWithTimeInterval: 1.0
invocation:inv
repeats:YES];
and after that, you start the timer manually whenever you need like this:
NSRunLoop *runner = [NSRunLoop currentRunLoop];
[runner addTimer: t forMode: NSDefaultRunLoopMode];
And as a note, onTick: method looks like this:
-(void)onTick:(NSTimer *)timer {
//do smth
}
Try this simple method:
- (void)viewDidLoad
{
[super viewDidLoad];
count = 0; // Declare int * count as global variable;
[NSTimer scheduledTimerWithTimeInterval:2 target:self selector:#selector(timerAction) userInfo:nil repeats:YES];
}
- (void)timerAction
{
[self custom_method:count++]
}
Might I suggest a different route. If you take the time since reference date, when the user enters the page:
NSTimeINterval time = [NSDate timeIntervalSinceReferenceDate]
then do the same when they leave the page and compare them.
timeOnPage = time - time2;
This is much more efficient than firing a timer on another thread unnecessary.
You do not need to use NSTimers for this at all.
Store the date/time when the user starts viewing, and calculate the time difference when they stop viewing using simple time arithmetic.
Exactly As Dave Wood says You should use date and time for starting and ending viewing that screen and calculate the difference and then save it to any integer variable.Using NSTimer will make the performance effect in your app and make the compiler busy while incrementing the count.
Hi I am trying to stop an NSTimer by using "invalidate" however from everything that I have tried I cant seem to get the timer to stop. Here is the code that I have to make this work. I am trying to stop the timer from a different class.
My Timer
_tripTimer = [NSTimer scheduledTimerWithTimeInterval:1.0
target:self
selector:#selector(updateTimerLabel:)
userInfo:[NSDate date]
repeats:YES];
which is synthesized and is strong
and the stopping method:
-(void)stopTimer
{
[_tripTimer invalidate];
}
and in my other class to get it to stop I am doing this:
[_carTripViewController stopTimer];
however that is not working. It is performing the method but not stopping the timer. Im not sure if i am creating a new instance and that is why it is not working. How can I get it to invalidate from another class?
Thank you! I am fairly new to objective-c and not sure how to access it
In the docoumentation about the invalidate method Apple says:
Special Considerations
You must send this message from the thread on which the timer was
installed. If you send this message from another thread, the input
source associated with the timer may not be removed from its run loop,
which could prevent the thread from exiting properly.
If you create the thread in the main method you can stop it in the main method by calling:
[self performSelectorOnMainThread:#selector(myMethod:)
withObject:anObj waitUntilDone:YES];
in your case something like:
[_carTripViewController performSelectorOnMainThread:#selector(stopTimer:)
withObject:nil waitUntilDone:YES];
I see two most probable causes:
1) You send stopTimer message to a different object of your class, not the one which where the timer has been launched.
2) _tripTimer variable doesn't point to the timer object any more, it points to somewhere else, probably to nil.
I had a similar problem and what I did was to add the timer to my appDelegade and use that as my timer context. Im not sure if this is academically 100% correct, but it works for me and is a workable hack at least. So far I haven't run into any problems and my app has been used extensively. See my code example:
if (!self.pollerTimer) {
self.pollerTimer = [NSTimer scheduledTimerWithTimeInterval:POLLER_INTERVAL
target:self
selector:#selector(performPollinginBackground)
userInfo:nil
repeats:YES];
//adds the timer variable and associated thread to the appDelegade. Remember to add a NSTimer property to your appDeledade.h, in this case its the pollerTimer variable as seen
NUAppDelegate *appDelegate = (NUAppDelegate *)[[UIApplication sharedApplication] delegate];
appDelegate.pollerTimer = self.pollerTimer;
}
Then when I want to stop the timer from anywhere in my app I can do the following:
NUAppDelegate *appDelegate = (NUAppDelegate *)[[UIApplication sharedApplication] delegate];
if (appDelegate.pollerTimer) {
[appDelegate.pollerTimer invalidate];
appDelegate.pollerTimer = nil;
}
I am trying to invoke a function that contains ccactioninterval in Cocos3d. I want to call that function at specific time intervals.When I tried NSTimer , i found that it works sometimes and sometimes not.
NSTimer makeTarget=[NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:#selector(createTargets) userInfo:nil repeats:YES];
Here createTargets is the function that contains action events. when i run the function straightit works fine for single time. Problem comes when i try to schedule it. I ve tried different methods already explained for related questions . But nothing worked for me. . . .
Here is the code
-(void) addTargets {
NSTimer *makeTarget = [NSTimer scheduledTimerWithTimeInterval:2.0
target:self selector:#selector(createTargets) userInfo:nil repeats:YES];
}
-(void)createTargets {
CC3MeshNode *target = (CC3MeshNode*)[self getNodeNamed: #"obj1"];
int minVal=-5;
int maxVal=5;
float avgVal;
avgVal = maxVal- minVal;
float Value = ((float)arc4random()/ARC4RANDOM_MAX)*avgVal+minVal ;
[target setLocation:cc3v(Value, 5.0, 0.0)];
CCActionInterval *moveTarget = [CC3MoveBy actionWithDuration:7.0 moveBy:cc3v(0.0, -10.0, 0.0)];
CCActionInterval *removeTarget = [CCCallFuncN actionWithTarget:self selector:#selector(removeTarget:)];
[target runAction:[CCSequence actionOne:moveTarget two:removeTarget]];
}
-(void)removeTarget:(CC3MeshNode*)targ {
[self removeChild:targ];
targ=nil;
}
Without much code its hard to tell what you issues is, but here are some things to try apologies if any of this is obvious.
Are you holding onto a reference to the timer?
This might be useful for debugging. If you have a property called makeTargetTimer, then you could do this:
NSTimer * makeTargetTimer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:#selector(createTargets) userInfo:nil repeats:YES];
self.makeTargetTimer = makeTargetTimer // Save to a property for later use (or just use an iVar)
The only way to stop a re-occurring timer is to invalidate it. Therefore you could check to see if its been invalidated.
BOOL isInvalidated = [self.makeTargetTimer isValid];
Also you might want to do this in your dealloc method anyway:
- (void) dealloc {
[_makeTargetTimer invalidate]; // Stops the timer from firing (Assumes ARC)
}
Are you scrolling when the even should be received?
If you want the timer to be fired while scrolling then you need to use NSRunLoopCommonModes. There is a excellent expiation in this question.
[[NSRunLoop currentRunLoop] addTimer:makeTargetTimer forMode:NSRunLoopCommonModes];
What is your implementation of createTargets like?
Have you put NSLog statements on the body of this method. Are you certain its not being called?
I'm working on a project, where i have to update the text of a UILabel really regularly (0.085f). So, I insert the update of the label in a loop like this :
MetresNumber = MetresNumber + 0.25;
DisplayMetres.text = [NSString stringWithFormat:#"%07.0f", MetresNumber];
I precise that "MetresNumber" is a float, and "DisplayMetres" the UILabel.
And this sort of code really really makes bad performances ! It's incredible how slower it goes since i've added those lines.
I made some searches, and found elements like :
[DisplayMetres setNeedsDisplay];
But it didn't change and update the text on the label.
It's in a loop called with :
timer = [NSTimer scheduledTimerWithTimeInterval:0.085 target:self selector:#selector(myLoop) userInfo:nil repeats:YES];
So my question is, could my code be improve, to get better performances, or should i forget my UILabel because it's too slow with ?
Thanks !
(void)setNeedsLayout
Call this method on your application’s main thread when you want to adjust the layout of a view’s subviews. This method makes a note of the request and returns immediately. Because this method does not force an immediate update, but instead waits for the next update cycle, you can use it to invalidate the layout of multiple views before any of those views are updated. This behavior allows you to consolidate all of your layout updates to one update cycle, which is usually better for performance.
Another problem is that a scheduledTimer will not get called while the main thread is tracking touches. You need to schedule the timer in the main run loop.
So instead of doing
[NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:#selector(updateLabel:) userInfo:nil repeats:YES];
use
NSTimer* timer = [NSTimer timerWithTimeInterval:1.0f target:self selector:#selector(updateLabel:) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
Also Use Timer selector method like below:
- (void) updateLabel:(id) sender {
MetresNumber = MetresNumber + 0.25;
NSString *text = [NSString stringWithFormat:#"%07.0f", MetresNumber];
dispatch_sync(dispatch_get_main_queue(), ^{
DisplayMetres.text = text;
});
}
There shouldn't be any performance issues when you are just updating a single label every 85ms. First find out what actually causes the lags. Use the Time Profiler instrument.
I think most time will be spent on the string drawing.
Here are some tips how you can optimize your code:
You don't need to call setNeedsLayout or setNeedsDisplay explicitely on the label. Just set the text property (on the main thread of course).
The resulting string in your code will always be a 7-digit integer. Consider using an integer instead of a float. Formatting an integer will be faster.
stringWithFormat can be slow sometimes. You could try using a NSNumberFormatter or simply generate the string with: [#(MetresNumber) stringValue]
In your code the string actually doesn't change everytime the timer fires. Only every 4th time. You can set the time interval to 4*0.085 and replace MetresNumber = MetresNumber + 0.25 with MetresNumber = MetresNumber + 1.
Try using this custom UILabel class
Don't use UILabel at all. Use pre-drawn images for each digit.
Schedule the timer with NSRunLoopCommonModes (see answer from Lightygalaxy)