I am repeating a function again and again using this code
- (void)refresh {
[self performSelector:#selector(refresh) withObject:nil afterDelay:5.0];
}
On viewWillDisappear I wrote the code to cancel this but still the function called. How can we cancel this perform selector repeating itself ?
- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:#selector(refresh) object:nil];
}
please First of all , check this you might be running on different run loops in creation and cancellation.I faced this problem in past.
or
I think no need to write selector again. Just right this and try.
With this
// cancel the above call (and any others on self)
[NSObject cancelPreviousPerformRequestsWithTarget:self];
Refer apples document.
NSObject_Class
Discussion All perform requests are canceled that have the same target
as aTarget, argument as anArgument, and selector as aSelector. This
method removes perform requests only in the current run loop, not all
run loops.
Related
In viewDidAppear I show a popup to users after 3 seconds. What if user navigates to another viewController after timer begins. The selected function will try to execute & show popup when superview is no longer on screen. App does not crash or throw any errors but I want to confirm this is safe. Should I set a BOOL and assert isCurrentView is YES, within selector method?
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
[self performSelector:#selector(showPopup) withObject:nil afterDelay:2.5];
}
in viewDidDisappear
-(void)viewDidDisappear:(BOOL)animated {
[super viewDidDisappear:(BOOL)animated];
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:#selector(showPopup) object:nil];
}
I dont know if this is possible... I have this code in touchesEnded:
[self performSelector:#selector(GameOver) withObject:nil afterDelay:3];
However, if you touch the screen again before the 3 seconds is up, I want to cancel the calling of GameOver. Any idea how I can do this.
In touchesBegan, I tried something like this:
[NSObject cancelPreviousPerformRequestsWithTarget:self
selector:#selector(touchesEnded:withEvent:)
object:nil];
This did not work.
Your selector value is wrong in your cancelPreviousPerformRequestsWithTarget call, that's all. If the original selector in performSelector was GameOver then obviously the perform request you are canceling must be specified as GameOver.
This is perfectly clear from the documentation: https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/index.html#//apple_ref/occ/clm/NSObject/cancelPreviousPerformRequestsWithTarget:selector:object:
I'm getting data off the server via JSON and displaying it on Labels.
I've added that method in viewDidLoad.
I want to refresh the data when the user opens the app again. Currently, even if I kill the app in the simulator and start the app again, it doesn't refresh.
I tried the viewDidAppear method, but it isn't being executed for some reason.
-(void)viewDidAppear{
NSLog(#"Called viewDidAppear");
}
This is never called. I tried to minimize the app but it didn't work.
You can listen for notifications and respond appropriately. Try using these and decide what works for your intended workflow.
UIApplicationDidBecomeActiveNotification
UIApplicationWillEnterForegroundNotification
You can use respond to the notification like this.
[[NSNotificationCenter defaultCenter] addObserverForName: UIApplicationDidBecomeActiveNotification object: nil queue: [NSOperationQueue mainQueue] usingBlock:^(NSNotification *note) {
// LOAD JSON
}];
I followed this tutorial - http://leejon.es/notifying-a-viewcontroller-with-uiapplicationdidbecomeactivenotification/
First, attach to the notification in the viewWillAppear method of the target view controller:
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[[NSNotificationCenter defaultCenter] addObserver: self
selector: #selector( appActivated: )
name: UIApplicationDidBecomeActiveNotification
object: nil];
}
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[[NSNotificationCenter defaultCenter] removeObserver:self ];
}
- (void)appActivated:(NSNotification *)note
{
[self update];
}
The viewDidAppear: method takes a bool parameter wether the view was displayed with an animation which you are missing. Also you have to call the implementation of the superclass:
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear: animated];
NSLog(#"Called viewDidAppear");
}
In your app delegate implementation, there is a method called:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions;
This method is called each time the app is launched, so I think it fits your needs. If you place your code here, it should work.
Also, be aware you should not perform a synchronous call here, because you will delay the app launch.
EDIT:
This method will be only called when the app launches. You could place your code inside a method, and call it from application didFinishLaunchingWithOptions, and then also call it from the method:
- (void)applicationWillEnterForeground:(UIApplication *)application;
This method will be called when the application enters the foreground, but not after the first launch, so beware.
I also think you should check the UIApplicationDelegate methods from apple developer page: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIApplicationDelegate_Protocol/Reference/Reference.html
Also, check out the application state changes:
http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html
I have 3 screens on my app.First is login. Second is search and third is process the task.
On login i retrieve data from a web service. It returns data in XML format. So the data is considerably large. So i am doing that task on a background thread like this to stop Mainthread freezing up on me:
-(BOOL)loginEmp
{
.....some computation
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
(unsigned long)NULL), ^(void) {
[self getAllCustomerValues];
});
}
-(void)getAllCustomerValues
{
....more computation.Bring the data,parse it and save it to CoreData DB.
//notification - EDIT
NSNotification *notification =[NSNotification notificationWithName:#"reloadRequest"
object:self];
[[NSNotificationCenter defaultCenter] postNotification : notification];
}
//EDIT
//SearchScreenVC.m
- (void)viewDidLoad
{
....some computation
[self.customerActIndicator startAnimating];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(stopActivityIndicator)
name:#"reloadRequest"
object:nil];
}
- (void)stopActivityIndicator
{
[self.customerActIndicator stopAnimating];
self.customerActIndicator.hidesWhenStopped = YES;
self.customerActIndicator.hidden =YES;
NSLog(#"HIt this at 127");
}
So on condition that login was successful, i move to screen 2. But the background thread is still in process( i know because i have logs logging values) . I want an activity indicator showing up here (2nd screen)telling user to wait before he starts searching. So how do i do it?How can i make my activity indicator listen/wait for background thread. Please let me know if you need more info.Thanks
EDIT: so I edited accordingly but the notification never gets called. I put a notification at the end of getAllCustomerValues and in viewDidLoad of SearchScreen i used it. That notification on 2nd screen to stop animating never gets called. What is the mistake i am doing.?Thanks
EDIT 2: So it finally hits the method. I dont know what made it to hit that method. I put a break point. I wrote to stop animating but it wouldn't. I wrote hidesWhenStoppped and hidden both to YES. But it still keeps animating.How do i get it to stop?
Ok, if it is not the main thread, put the following in and that should fix it.
- (void)stopActivityIndicator
{
if(![NSThread isMainThread]){
[self performSelectorOnMainThread:#selector(stopActivityIndicator) withObject:nil waitUntilDone:NO];
return;
}
[self.customerActIndicator stopAnimating];
self.customerActIndicator.hidesWhenStopped = YES;
self.customerActIndicator.hidden =YES;
NSLog(#"HIt this at 127");
}
Could you put your background operation into a separate class and then set a delegate on it so you can alert the delegate once the operation has completed?
I havent tried this, its just an idea :)
You could use a delegate pointing to your view controller & a method in your view controller like:
- (void) updateProgress:(NSNumber*)percentageComplete {
}
And then in the background thread:
float percentComplete = 0.5; // for example
NSNumber *percentComplete = [NSNumber numberWithFloat:percentComplete];
[delegate performSelectorOnMainThread:#selector(updateProgress:) withObject:percentageComplete waitUntilDone:NO];
I am using a UIWebView and don't want the navigation bar to appear unless the user taps anywhere on the screen that isn't a link.
So I have this code to display the navigation bar after a delay:
- (void)handleTapGesture:(UITapGestureRecognizer *)sender
{
....
[self performSelector:#selector(showNavigationBar) withObject:self afterDelay:0.2];
}
I'm not calling showNavigationBar immediately when the tap handler is invoked because the user might have tapped on a link in which case the tap hander is called before UIWebView shouldStartLoadWithRequest, so if I hid the navigation bar in shouldStartLoadWithRequest it would flash momentarily onto the screen.
So instead I set it to display after a delay which gives time for the following code to execute within shouldStartLoadWithRequest (and if the user didn't tap on a link shouldStartLoadWithRequest isn't called and the navigation bar is displayed, as it should be in that case).
- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:#selector(showNavigationBar) object:nil];
...
However this isn't working, I've increased the delay time to several seconds and can confirm cancelPreviousPerformRequestWithTarget is getting called before the navigation bar has been displayed, but when the specified time elapses the bar displays. cancelPreviousPerformRequestWithTarget is having no effect.
Does anybody know why its not working?
Your perform doesn't match your cancel. In the perform you're passing self as the object:
[self performSelector:#selector(showNavigationBar) withObject:self afterDelay:0.2];
In the cancel you're passing nil as the object:
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:#selector(showNavigationBar) object:nil];
They don't match, so the delayed perform should not be canceled.
In the documentation of that + (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget selector:(SEL)aSelector object:(id)anArgument method there is this sentence :
This method removes perform requests only in the current run loop, not all run loops.
If I'm interpreting it correctly it would mean that you need to cancel your action in the same run loop that you launched it. Which is clearly not what you want to do.
A way to go around this would be to have a flag that showNavigationBar would have to check to see if it should proceed or abort.
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:#selector(showNavigationBar) object:self];
That worked for me ;)
Not sure why but works like a charm for me.
dispatch_async(dispatch_get_main_queue(), ^{
[NSObject cancelPreviousPerformRequestsWithTarget:self];
});