I have several dispatch_async methods linked so they authenticate a user in my system.
The next async method only happens when the previous one finishes, as they each have completion handlers.
When the last one is finished I perform a custom segue with 2 uiview animation blocks.
However, when I log when each of these actually run, there is a considerable gap between the log and the animation actually happening, eventually the views animate and the completion block is called.
I don't really know how useful it would be adding my code here, but i have tested and it must be the async methods because if I comment them out and just return YES the animations happen without delay at the same time as the log.
Does anyone know why this might happen?
EDIT *(with code)
Typical 'exist check' used for email, user, user id.
- (void)existsInSystemWithCompletionHandler:(void (^)(BOOL))block
{
self.existsInSystem = NO;
if (self.isValid) {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//
// Get data
//
if (dataIsValid) {
block(YES);
} else {
block(NO);
}
});
} else {
block(self.existsInSystem);
}
}
Check user exists
[potentialUser existsInSystemWithCompletionHandler:^(BOOL success) {
if (success) {
// Perform segue
//
[self performSegueWithIdentifier:#"Logging In" sender:self];
}
}];
Segue
- (void)perform
{
NSLog(#"Perform");
LogInViewController *sourceViewController = (LogInViewController *)self.sourceViewController;
LoggingInViewController *destinationViewController = (LoggingInViewController *)self.destinationViewController;
destinationViewController.user = sourceViewController.potentialUser;
// Animate
//
[UIView animateWithDuration:0.2f
animations:^{
NSLog(#"Animation 1");
//
// Animate blah blah blah
//
}];
[UIView animateWithDuration:0.4f
delay:0.0f
options:UIViewAnimationOptionCurveEaseIn
animations:^{
NSLog(#"Animation 2");
//
// Animate blah blah blah
//
}
completion:^(BOOL finished) {
NSLog(#"Completion");
//
// Finished
//
[sourceViewController presentViewController:destinationViewController animated:NO completion:nil];
}];
}
LoggingIn VC
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
[self.user loginWithCompletionHandler:^(BOOL success) {
if (success) {
[self performSegueWithIdentifier:#"Logged In" sender:self];
}
}];
}
Fixed! It seems to work now that in my code I have added the lines:
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock(success);
});
From your description it seems likely that your segue is waiting for a process to finish.
Maybe your nested async methods that follow each other through their completion methods have produced somewhat convoluted code. This might be the reason why you could be overlooking the blocking method.
One way to tidy up your code is use a sequential queue. The blocks pushed to the queue will start only when the previous one has finished.
Related
I'm delaying UIKit messages as per this SO answer
Now another requirement has arisen, instead of just queuing SSHUDView method calls we should also handle queing of UIAlertView. For example one scenario could be that we display a hud then after 1 second we display another hud and then finally after 1 second we display a UIAlertView.
The problem is now that since the SSHUDViews are run asynchronously on a background thread when I get to display the UIAlertView the SSHUDViews have not finished displaying so the UIAlertView will overlay the hud.
Basically I need a way to queue up and delay methods whether they are of class SSHUDView or UIAlertView. A feedback queue, where you can delay individual messages.
What you're talking about sounds like a perfect fit for semaphores (see under the heading Using Dispatch Semaphores to Regulate the Use of Finite Resources)! I saw the SO Answer you linked to and I don't think it solves the case of UIView animations. Here's how I'd use semaphores.
In your view controller add an instance variable dispatch_semaphore_t _animationSemaphore; and initialize it in the - init method:
- (id)init
{
if ((self = [super init])) {
_animationSemaphore = dispatch_semaphore_create(1);
}
return self;
}
(Don't forget to release the semaphore in the - dealloc method using dispatch_release. You also might want to wait for queued animations to finish by using dispatch_semaphore_wait, but I'll leave that for you to figure out.)
When you want to queue up an animation, you'll do something like this:
- (void)animateSomething
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
dispatch_semaphore_wait(_animationSemaphore, DISPATCH_TIME_FOREVER);
dispatch_async(dispatch_get_main_queue(), ^{
[UIView animateWithDuration:0.5 animations:^{
// Your fancy animation code
} completion:^(BOOL finished) {
dispatch_semaphore_signal(_animationSemaphore);
}];
});
});
}
You can use the - animateSomething template to accomplish different things, such as displaying an SSHUDView or a UIAlertView.
What you're describing sounds like an animation. Why not just use UIView animation and chain the series of animation blocks:
[UIView animateWithDuration:2
animations:^{
// display first HUD
}
completion:^(BOOL finished){
[UIView animateWithDuration:2
animations:^{
// hide first HUD, display second HUD
}
completion:^(BOOL finished){
[UIView animateWithDuration:2
animations:^{
// hide second HUD, show UIAlert
}
completion:nil
];
}
];
}
];
When programming for iOS, I frequently find myself faced with the following situation:
- (void)someMethod
{
[self performSomeAnimation];
//below is an action I want to perform, but I want to perform it AFTER the animation
[self someAction];
}
- (void)performSomeAnimation
{
[UIView animateWithDuration:.5 animations:^
{
//some animation here
}];
}
Faced with this situation, I usually end up just copy/pasting my animation code so that I can use the completion block handler, like so:
- (void)someMethod
{
[self performSomeAnimation];
//copy pasted animation... bleh
[UIView animateWithDuration:.5 animations:^
{
//same animation here... code duplication, bad.
}
completion^(BOOL finished)
{
[self someAction];
}];
}
- (void)performSomeAnimation
{
[UIView animateWithDuration:.5 animations:^
{
//some animation here
}];
}
What is the proper way to solve this problem? Should I be passing a block of code to my -(void)performSomeAction method, like below, and executing that block on completion of the animation?
- (void)someMethod
{
block_t animationCompletionBlock^{
[self someAction];
};
[self performSomeAnimation:animationCompletionBlock];
}
- (void)performSomeAnimation:(block_t)animationCompletionBlock
{
[UIView animateWithDuration:.5 animations:^
{
//some animation here
}
completion^(BOOL finished)
{
animationCompletionBlock();
}];
}
Is that the proper way to solve this problem? I guess I have been avoiding it because I'm not THAT familiar with block usage (not even sure if I declared that block properly) and it seems like a complicated solution to a simple problem.
You could also do this:
- (void)performSomeAnimationWithCompletion:(void(^)(void))animationCompletionBlock
{
[UIView animateWithDuration:.5 animations:^
{
//some animation here
}
completion^(BOOL finished)
{
animationCompletionBlock();
}];
}
And instead of explicitly defining a block and passing it as parameter, you can call it directly like this (this is how block animations work for UIView, for example):
- (void)someMethod
{
[self performSomeAnimationWithCompletion:^{
[self someAction];
}];
}
From what I can understand, it seems that you already pretty much have the answer, you just need to delete the first call to performSomeOperation :
- (void)someMethod
{
[UIView animateWithDuration:.5 animations:^
{
//Your animation block here
}
completion: ^(BOOL finished)
{
//Your completion block here
[self someAction];
}];
}
In Grand Central Dispatch I want to start a spinner - UIActivityIndicatorView - spinning prior to beginning long running task:
dispatch_async(cloudQueue, ^{
dispatch_async(dispatch_get_main_queue(),
^{
[self spinnerSpin:YES];
});
[self performLongRunningTask];
dispatch_async(dispatch_get_main_queue(),
^{
[self spinnerSpin:NO];
});
});
Here is the spinnerSpin method:
- (void)spinnerSpin:(BOOL)spin {
ALog(#"spinner %#", (YES == spin) ? #"spin" : #"stop");
if (spin == [self.spinner isAnimating]) return;
if (YES == spin) {
self.hidden = NO;
[self.spinner startAnimating];
} else {
[self.spinner stopAnimating];
self.hidden = YES;
}
}
One thing I have never seen discussed is the difference - if any - between [myView setNeedsDisplay] and [myActivityIndicatorView startAnimating]. Do they behave the same?
Thanks,
Doug
The [UIView setNeedsDisplay] method has nothing to do with a UIActivityIndicatorView's animation state.
setNeedsDisplay simply informs the system that this view's state has changed in a way that invalidates its currently drawn representation. In other words, it asks the system to invoke that view's drawRect method on the next drawing cycle.
You very rarely need to invoke setNeedsDisplay from outside of a view, from code that is consuming the view. This method is meant to be invoked by the view's internal logic code, whenever something changes in its internal state that requires a redraw of the view.
The [UIActivityIndicatorView startAnimating] method is specific to the UIActivityIndicatorView class and simply asks the indicator to start animating (e.g. spinning). This method is instant, without requiring you to call any other method.
On a side note, you could simplify your code by simply calling startAnimating or stopAnimating without manually showing/hiding it. The UIActivityIndicatorView class has a hidesWhenStopped boolean property that defaults to YES, which means that the spinner will show itself as soon as it starts animating, and hide itself when it stops animating.
So your spinnerSpin: method could be refactored like this (as long as you haven't set the hidesWhenStopped property to NO):
- (void)spinnerSpin:(BOOL)spin {
if (YES == spin) {
[self.spinner startAnimating];
} else {
[self.spinner stopAnimating];
}
}
I am having an issue dismissing a modal view controller on a certain edge case. I display the modal view when I am retrieving a PDF to display in a UIWebView. When the file I am retrieving is very small the modal view will try to dismiss too soon. I present the modal view in the view controller that contains the UIWebView. I dismiss it in the UIWebView's didFinishLoad delegate method.
I am fine with not animating the initial presentation of the modal view... but is that any more safe than what I was doing? does this still have potential to fail, and if so how would you change it? I have been looking through the docs and nothing I have read so far adresses this situation.
//
// This will download the file if not # specific path, otherwise use local file.
// _myFileManager is a helper class and _myFileRecord is the backing data model
//
-(id)initWithNib... fileRecord:(MYFileRecord *)_myFileRecord
{
[_myFileManager cacheFileAsync:_myFileRecord delegate:self];
}
- (void)viewDidLoad
{
// doesn't seem to work, NO for animated does seem to work
[self.navigationController presentModalViewController:_splashController
animated:YES];
_splashController.messageLabel.text = #"Retrieving File...";
}
- (void)recordSaved:(MyFileRecord *)myFileRecord fileName:(NSString *)fileName
{
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL fileURLWithPath:fileName]];
[_webView loadRequest:request];
}
- (void)webViewDidStartLoad:(UIWebView *)webView {
_splashController.messageLabel.text = #"Opening File...";
}
//
// This fails when a small file is already cached to disk and the time
// for the webView to finishLoad is faster than the splashView can present itself
//
- (void)webViewDidFinishLoad:(UIWebView *)webView {
[self.navigationController dismissModalViewControllerAnimated:YES];
}
Try implementing the viewDidAppear in your SplashController, to catch when the view has finished animating, and set a flag. Then you can control if the SplashController's view has finished loading using this flag, and wait for it if it is not finished yet?
E.g.
-(void)viewDidAppear {
if (shouldDismiss) {
[self dismissViewControllerAnimated:YES];
}
readyToDismiss = YES;
}
And in your main VC:
-(void)webViewDidFinishLoading:(UIWebView*)webViewv
{
if (_splashController.readyToDismiss) {
[_splashController dismissViewControllerAnimated:YES];
} else {
_splashController.shouldDismiss = YES; // will dismiss in viewDidAppear
}
}
You can try testing to see if the splashView has finished and use performSelector:afterDelay: to check back later.
My idea is to create a method like this
-(void)dismissWhenReady {
if ( splashView is finished) {
[self.navigationController dismissModalViewControllerAnimated:YES];
} else
[self performSelector:#selector(dismissWhenReady) afterDelay:1.0];
}
}
viewDidLoad fires too early (before it is displayed), you will want to use -(void)viewDidAppear:(BOOL)animated to present your modal view instead along with a flag to know if it is the first load. If it still does not display long enough add a delay for the desired amount of time.
This is very strange. My view is receiving a notification with an index number that I use to find a UIbutton by tag and then change its text label. The only trouble is the text will not change. I've put in break points and the code is being executed.
Is there some peculiarity with variable scopes when using notifications?
- (void)receiveEvent:(NSNotification *)notification {
int pass = [[[notification userInfo] valueForKey:#"index"] intValue];
NSLog(#"button index is %i", pass);
UIButton *changebut = (UIButton *) [self.view viewWithTag:pass];
ButtonStatusModel *m= [self.buttoneventpendingarray objectAtIndex:pass];
NSLog(#"current but status = %i",m.btnstatus);
if (m.btnstatus==3 ) {
//this should change the label but it does not;
[changebut setTitle:#"playing" forState:UIControlStateNormal];
m.btnstatus=2;
NSLog(#"should set text to 'playing");
//[engine addActionToQue:buttonid actionSample:actionsample action:1];
}else if (m.btnstatus==1) {
//this should change the label but it does not;
[changebut setTitle:#"idle" forState:UIControlStateNormal];
NSLog(#"should set text to 'idle");
m.btnstatus=0;
//[engine addActionToQue:buttonid actionSample:actionsample action:0];
}
}
EDIT 1
Thanks to commenters I've determined that even though my reciveevent function in on my main view controller the function is not being executed from the main thread (dont really understand this) and so thats why the button label will not change.
I used the following code to determine if it was the main thread or not. I think now to change the button label I need to call perform selector on main thread? Is this the correct thing to do? If so I need to pass a function 2 variables, I dont see how perform selector on main thread accomodates this.
-(void) updatebutton:(int)tag changeto:(int) val
{
if ([NSThread isMainThread]) {
{
NSLog(#"is main thread");
}
} else {
NSLog(#"is not thread");
[self performSelectorOnMainThread:#selector( /*function with 2 parameters here*/) withObject:nil waitUntilDone:YES];
}
}
EDIT 3*
Using blocks instead of main selector helped me out of my problem.
I really don't understand the whole main thread though. I assumed that if code was in my view controller that any executed code would be performed on the main thread. That seems to be big fat wrong. I would appreciate a little enlightenment on the matter.
Heres what I used anyway
-(void) updatebutton:(int)tag changeto:(int) val
{
UIButton *changebut = (UIButton *) [self.view viewWithTag:tag];
if ([NSThread isMainThread]) {
{
NSLog(#"is main thread");
if (val==2) {
[changebut setTitle:#"playing" forState:UIControlStateNormal];
}
if (val==0) {
[changebut setTitle:#"idle" forState:UIControlStateNormal];
}
}
} else {
NSLog(#"is not thread");
//[self performSelectorOnMainThread:#selector(updatebutton::) withObject:nil waitUntilDone:YES];
if (val==2) {
dispatch_async(dispatch_get_main_queue(), ^{
[changebut setTitle:#"playing" forState:UIControlStateNormal];
});
}
if (val==0) {
dispatch_async(dispatch_get_main_queue(), ^{
[changebut setTitle:#"idle" forState:UIControlStateNormal];
});
}
}
}
Try putting
[changebut setTitle:#"idle" forState:UIControlStateNormal];
in the -viewDidAppear method. If it doesn't work either, make sure that all the outlets are connected in IB. Moreover, try adding a few spaces as the button title in your .xib file (if you have one).
Is -receiveEvent called on another than the main thread? UI changes must be performed on the main thread.