In a project I'm writing I get this error when I present a new view controller:
Attempt to present.... while a presentation is in progress!
I think it happens because I first present a new view controller, and then in that view I present another view controller.
- (void)loadLabelSettings {
LabelSettingsViewController *labelSettings =
[[LabelSettingsViewController alloc] init];
labelSettings.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
[self presentViewController:labelSettings animated:YES completion:nil];
}
The program doesn't crash or anything it runs just fine, and there is no errors or warnings in my code. So my question is: Is it something I should be concerned with and if yes how do I solve it?
Thanks in advance :)
It is, like you said, probably caused by presenting two view controllers at the same time. Wait with presenting the second view controller until the first one has been fully presented. A good location would be to do this in viewDidAppear.
In my case, I connected a UIViewControllers UIButton with a second UIViewController by a UIStoryboardSegue. Inside my code a called it a second time programmatically. So pressing the UIButton caused presenting the specified view two times.
I figured out my problem, as Scott wrote it was because I was presenting 2 view controllers at the same time. It happened because I had a button that had a UILongPressGestureRecognizer, that showed the new view controller. The problem was that when using a UILongPressGestureRecognizer, the method that is being called, is called twice. First when the long press is detected and when your finger is released from the screen. So the presentViewController method of the same view, was called twice. I fixed this by only reacting to the first detection. Here is the code :
- (void)loadButtonSettings:(UILongPressGestureRecognizer *)recognizer {
if (recognizer.state == UIGestureRecognizerStateBegan) {
}
}
Related
I have an app that has an initial login screen then when the user wants to sign up, they are presented with a registration form that is three view controllers presented modally. When the user completes the form on the third screen (by pressing a "Done" button), I want the user to be taken back to the initial login screen.
I have tried doing this in the third view controller:
[self dismissViewControllerAnimated:NO completion:nil]
[self.presentingViewController dismissViewControllerAnimated:NO completion:nil]
[self.presentingViewController.presentingViewController dismissViewControllerAnimated:NO completion:nil]
However it only dismissed two of the view controllers and not all 3. Why did this happen?
As other people pointed out, there are more elegant/efficient/easier ways to achieve similar results from the UX perspective: via a navigation controller, or a page view controller, or other container.
Short/quick answer: you need to go one step further in the chain of presenting view controllers, because the dismissal request needs to be sent to the controller that's presenting, and not to the one that's being presented. And you can send the dismiss request to that controller only, it will take care of popping from the stack the child controllers.
UIViewController *ctrl = self.presentingViewController.presentingViewController.presentingViewController;
[ctrl dismissViewControllerAnimated:NO completion:nil]
To explain why, and hopefully help other people better understand the controller presenting logic in iOS, below you can find are more details.
Let's start from Apple documentation on dismissViewControllerAnimated:completion:
Dismisses the view controller that was presented modally by the view controller.
The presenting view controller is responsible for dismissing the view controller it presented. If you call this method on the presented view controller itself, UIKit asks the presenting view controller to handle the dismissal.
Thus [self dismissViewControllerAnimated:NO completion:nil] simply forwarded the request to self.presentingViewController. Which means the first two lines had the same effect (actually the 2nd line did nothing as there was no presented controller after the 1st one executed).
This is why your dismissal of view controllers worked only the top 2 ones. You should've start with self.presentingViewController and go along the chain of presenting view controllers. But this is not very elegant and can cause problems if later on the hierarchy of view controllers changes.
Continuing to read on the documentation, we stumble upon this:
If you present several view controllers in succession, thus building a stack of presented view controllers, calling this method on a view controller lower in the stack dismisses its immediate child view controller and all view controllers above that child on the stack.
So you needn't call dismissViewControllerAnimated:completion: three times, a call on the controller that you want to come back will suffice. At this point, passing a reference to that controller would be more reliable than navigating through the stack of view controllers.
There are some more useful details in the documentation, for example regarding what transitions apply when dismissing multiple controllers at once.
I recommend you go through the whole documentation, not only for this method, but for all methods/classes that you use in your application. You'll likely discover things that will make your life easier.
And if you don't have the time to read all Apple's documentation on UIKit, you can read it when you run into problems, like in this case with dismissViewControllerAnimated:completion: not working as you thought it would.
As a closing note, there are some more subtle issues with your approach, as the actual dismissal takes place in another runloop cycle, as it's possible to generate console warnings and not behave as expected. This is why further actions regarding presenting/dismissing other controllers should be done in the completion block, to give a change to UIKit to finish updating its internal state.
Totally understood. What I will do is embed a navigation controller instead of using modal. I have a case just like you. I have LoginViewController to be the root view controller of the UINavigationController. SignupViewController will be presented by push method. For ResetPasswordViewController, I will use modal because it's supposed to go back to LoginViewController no matter the results. Then, you can dismiss the whole UINavigationController from SignupViewController or LoginViewController.
Second approach will be like, you come up with your own mechanism to reference the presented UIViewController via a shared instance. Then, you can easily dismiss it. Be careful with the memory management. After dismissing it, you should consider whether you need to nil it right away.
I know three ways to dismiss several viewControllers:
Use a chain of completion blocks
~
UIViewController *theVC = self.presentingViewController;
UIViewController *theOtherVC = theVC.presentingViewController;
[self dismissViewControllerAnimated:NO
completion:^
{
[theVC dismissViewControllerAnimated:NO
completion:^
{
[theOtherVC dismissViewControllerAnimated:NO completion:nil];
}];
}];
Use 'viewWillAppear:' method of viewControllers
~
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
if (self.shouldDismiss)
{
CustomVC *theVC = (id)self.presentingViewController;
theVC.shouldDismiss = YES;
[self dismissViewControllerAnimated:NO completion:nil];
}
}
Pass a reference to LoginVC1 further down the chain.
(This is the best approach so far)
Imagine you have some StandardVC, which presented LoginVC1.
Then, LoginVC1 presented LoginVC2.
Then, LoginVC2 presented LoginVC3.
An easy way of doing what you want would be to call (from inside your LoginVC3.m file)
[myLoginVC1 dismissViewControllerAnimated:YES completion:nil];
In this case your LoginVC1 would lose its strong reference (from StandardVC), which means that both LoginVC2 and LoginVC3 would also be deallocated.
So, all you need to do is let your LoginVC3 know that LoginVC1 exists.
If you don't want to pass a reference of LoginVC1, you can use:
[self.presentingViewController.presentingViewController dismissViewControllerAnimated:NO completion:nil];
However, the above approaches are NOT the correct ways of doing what you want to do.
I would recommend you doing the following:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
if (!self.isUserLoggedIn)
{
[UIApplication sharedApplication].keyWindow.rootViewController = self.myLoginVC;
}
return YES;
}
Then, when user finished his login process, you can use
[UIApplication sharedApplication].keyWindow.rootViewController = self.myUsualStartVC;
I'm attempting to convert our application to storyboards and have hit what I believe is a bug in the handling of unwind segues when dealing with custom container controllers. We have a view controller which displays another and uses the view controller containment api to do this, I wire up the segue in IB then select a custom class for the implementation. The perform method looks something like this:
-(void) perform {
UIViewController *container = [self sourceViewController];
UIViewController *child = [self destinationViewController];
[container addChildViewController:child];
[container.view addSubview:child.view];
child.view.center = container.view.center;
[UIView transitionWithView:container.view
duration:0.35
options:UIViewAnimationOptionCurveEaseInOut
animations:^{
child.view.alpha = 1;
} completion:^(BOOL finished) {
[child didMoveToParentViewController:container];
}];
}
That works perfectly, however I can't make it perform the unwind segue back to the container controller. I override viewControllerForUnwindSegueAction: fromViewController: withSender: and ensure that it's returning the correct value:
-(UIViewController *) viewControllerForUnwindSegueAction:(SEL)action fromViewController:(UIViewController *)fromViewController withSender:(id)sender {
id default = [super viewControllerForUnwindSegueAction:action fromViewController:fromViewController withSender:sender];
NSAssert1(default == self, #"Expected the default view controller to be self but was %#", default);
return default;
}
I can also confirm that canPerformUnwindSegueAction:fromViewController:withSender is being called and doing the right thing, but to be sure I overrode it to return YES
-(BOOL) canPerformUnwindSegueAction:(SEL)action fromViewController:(UIViewController *)fromViewController withSender:(id)sender {
return YES;
}
The next step I would expect to happen is for segueForUnwindingToViewController:fromViewController:identifier: to be called, however it never is. Instead the application crashes with an NSInternalInconsistencyException.
2012-10-01 10:56:33.627 UnwindSegues[12770:c07] *** Assertion failure in -[UIStoryboardUnwindSegueTemplate _perform:], /SourceCache/UIKit_Sim/UIKit-2372/UIStoryboardUnwindSegueTemplate.m:78
2012-10-01 10:56:33.628 UnwindSegues[12770:c07] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Could not find a view controller to execute unwinding for <USCustomContainerViewController: 0x75949a0>'
*** First throw call stack:
(0x1c8e012 0x10cbe7e 0x1c8de78 0xb61f35 0x581711 0x45ab54 0x10df705 0x16920 0x168b8 0xd7671 0xd7bcf 0xd6d38 0x4633f 0x46552 0x243aa 0x15cf8 0x1be9df9 0x1be9ad0 0x1c03bf5 0x1c03962 0x1c34bb6 0x1c33f44 0x1c33e1b 0x1be87e3 0x1be8668 0x1365c 0x1e7d 0x1da5)
libc++abi.dylib: terminate called throwing an exception
Has anyone successfully used unwind segues combined with the view controller containment APIs? Any idea what step I'm missing? I've uploaded a demo project to github which shows the issue in the simplest demonstration project I could come up with.
The problem in your example is that there's no there there. It's too simple. First, you create your container view controller in a rather odd way (you don't use the new IB "container view" which is there to help you do this). Second, you've got nothing to unwind: nothing was pushed or presented on top of anything.
I have a working example showing that canPerformUnwindSegueAction really is consulted up the parent chain, and that viewControllerForUnwindSegueAction and segueForUnwindingToViewController are called and effective, if present in the right place. See:
https://github.com/mattneub/Programming-iOS-Book-Examples/tree/master/ch19p640presentedViewControllerStoryboard2
I have now also created a fork of your original example on github, correcting it so that it illustrates these features:
https://github.com/mattneub/UnwindSegues
It isn't really a situation where "unwind" is needed, but it does show how "unwind" can be used when a custom container view controller is involved.
This seems to be a bug – I would also expect unwind segues to work as you implemented.
The workaround that I used is explicitly dismissing the presented view controller in the IBAction method:
- (UIStoryboardSegue *)segueForUnwindingToViewController:(UIViewController *)toViewController
fromViewController:(UIViewController *)fromViewController
identifier:(NSString *)identifier
{
return [[UIStoryboardSegue alloc] initWithIdentifier:identifier
source:fromViewController
destination:toViewController];
}
- (IBAction)unwind:(UIStoryboardSegue*)segue
{
UIViewController *vc = segue.sourceViewController;
[vc willMoveToParentViewController:nil];
if ([vc respondsToSelector:#selector(beginAppearanceTransition:animated:)]) {
[vc beginAppearanceTransition:NO animated:YES]; // iOS 6
}
UIView *modal = vc.view;
UIView *target = [[segue destinationViewController] view];
[UIView animateWithDuration:duration animations:^{
modal.frame = CGRectMake(0, target.bounds.size.height, modal.frame.size.width, modal.frame.size.height);
} completion:^(BOOL finished) {
[modal removeFromSuperview];
[vc removeFromParentViewController];
if ([vc respondsToSelector:#selector(endAppearanceTransition)]) {
[vc endAppearanceTransition];
}
}];
}
Brief history before the answer: I just ran into the same exact error message when trying to use multiple Container Views on one iPad screen in iOS 6 and calling unwind segues from code. At first I thought this may be a problem because my segue was created using Storyboards by CTRL-dragging from File Owner to Exit instead of from some UI control to Exit, but I got same results when I put test Close buttons on each VC and had them trigger the unwind segues. I realized that I'm trying to unwind an embed segue, not a modal/push/popup segue, so it makes sense that it fails to do it. After all, if the unwind segue succeeds and the view controller is unloaded from a Container View, iOS 6 thinks there'll just be an empty space on the screen in that spot. (In my case, I have another container view taking up screen real estate that's shown behind the container view which I'm trying to unload, but iOS doesn't know that since the two aren't connected in any way.)
Answer: this led me to realize that you can only unwind modal, push, or popover segues, be it within the main window or as part of a Navigation/Tab Controller. This is b/c iOS then knows that there was a previous VC responsible for the whole screen and it's safe to go back to it. So, in your case, I'd look into a way to tell iOS that your child container view is connected to your parent container view in a way that makes it safe to dismiss the child container view. For example, perform a modal/push/popover segue when displaying the child container view, or wrap both into a custom UINavigationController class (I assume you don't want the navigation bar, that's why custom class).
Sorry I can't give exact code, but this is the best I got to so far and I hope it's helpful.
Looks like this bug is fixed in iOS9.
Similar to this question: Adding subview, gets delayed?
But I don't think you can pushViewController in a separate thread so is this really impossible?
Here is what I'm trying to do:
I have a TableView and when a cell is pressed, I want to call
[self.view addSubview:LoadingView]
to display an overlay with a spinner. Then I call
self.navigationController.navigationBar.hidden = NO;
[self.navigationController pushViewController:newGameViewController animated:YES];
However, the subview only displays for a split second (~1-4 seconds after the cell selection occurs while it waits for the new viewcontroller to initialize).
Is there any way to get some sort of loading indicator to occur at the instant the cell is selected?
Okay. What about this. In your didSelectRowAtIndexPath start your spinner (via addSubview ...) and start loading your stuff from the server. If that's finished remove the spinner an push your new view controller onto the stack. Make sure the user can't touch any other cell during that time. By the way. From a users perspective I'd find it mor intuitive if the new controller is loaded immediately and displays some waiting message.
Or the other way around: The newGameViewController displays the spinner and starts loading the data from the server in a background thread. When the data is complete, remove the spinner and display the data. That way the user could even go back if she doesn't want to wait.
You do not need to add code before pushing newGameViewController.
Inside viewDidLoad of newGameViewController, write the code of displaying spinner. To get the updated UI, just insert a delay before calling a web API.
inside GameViewController.m
-(void) viewDidLoad
{
[self.view addSubview:LoadingView];
[self performSelector:#selector(callWebAPI) afterDelay:0.1];
}
-(void) callWebAPI
{
//Handle network activity here..
}
Say I have two view controllers: xVC and yVC. I have used the shake API and and have used the methods -(void)motionBegan,-(void)motionEnded: and -(void)motionCancelled in xVC. What happens is when the device is shaken, it fires a simple animation. Now the thing is that this animation is fired even when the I have yVC open that is, when yVS.view has been added as the subview. What I am looking for is some if condition which I can use in -(void)motionEnded: like this:
if(yVC == nil)
{
//trigger animation
}
By that I mean that the shake shouldn't work when yVC is visible. How do I do that? Please help.
The general advice I have seen and used is to ask a view if it has a non-nil window property:
if( ! yVC.view.window) {
// trigger animation
}
But note that this doesn't always equate with being visible; though in most apps it's about as good as you can performantly get (the basic case where it's not accurate is when a different view completely obscures it, but this may still satisfy your needs)
Add this to both of your view controllers:
-(void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
visible = YES;
}
-(void)viewDidDisappear:(BOOL)animated
{
[super viewDidDisappear:animated];
visible = NO;
}
Now, just check the variable isVisible of both the view controllers and trigger your animation likewise.
The previous answers all work to some degree, but fail to take modally presented view controllers into account. If view controller A presents view controller B, of the previous answers will tell you that A is still visible. If you, like me, want to know whether or not the view is actually visible (and not just a part of the view hierarchy), I would suggest also checking the presentedViewController property:
if (self.isViewLoaded && [self.view window] && !self.presentedViewController) {
// User is looking at this view and nothing else
}
This works since presentedViewController will be non-nil whenever the current view controller OR any of its ancestors are currently presenting another view controller.
I can't seem to figure this out for the life of me. I have a custom table view cell, in that cell I have a few buttons configured. Each button connects to other view controllers via a storyboard segue. I've recently removed these segues and put a pushViewController method in place. Transition back and forth across the various views works as expected however the destination view controller is not displaying anything! I have some code below as an example.
Buttons have this method set:
[cell.spotButton1 addTarget:self action:#selector(showSpotDetails:) forControlEvents:UIControlEventTouchUpInside];
// etc...
[cell.spotButton4 addTarget:self action:#selector(showSpotDetails:) forControlEvents:UIControlEventTouchUpInside];
// etc...
showSpotDetails Method contains this code:
- (void)showSpotDetails:(id)sender
{
// determine which button (spot) was selected, then use its tag parameter to determine the spot.
UIButton *selectedButton = (UIButton *)sender;
Spot *spot = (Spot *)[spotsArray_ objectAtIndex:selectedButton.tag];
SpotDetails *spotDetails = [[SpotDetails alloc] init];
[spotDetails setSpotDetailsObject:spot];
[self.navigationController pushViewController:spotDetails animated:YES];
}
The details VC does receive the object data.
- (void)viewDidLoad
{
[super viewDidLoad];
NSLog(#"spotDetailsObject %#", spotDetailsObject_.name);
}
The NSLog method below does output the passed object. Also, everything in the details view controller is as it was. Nothing has changed on the details VC. It just does not render anything ever since I removed the segue and added the pushViewController method. Perhaps I am missing something on the pushViewController method? I never really do things this way, I try to always use segues...
Any suggestions?
Welcome to the real world. Previously, the storyboard was a crutch; you were hiding from yourself the true facts about how view controllers work. Now you are trying to throw away that crutch. Good! But now you must learn to walk. :) The key here is this line:
SpotDetails *spotDetails = [[SpotDetails alloc] init];
SpotDetails is a UIViewController subclass. You are not doing anything here that would cause this UIViewController to have a view. Thus you are ending up a with blank generic view! If you want a UIViewController to have a view, you need to give it a view somehow. For example, you could draw the view in a nib called SpotDetails.xib where the File's Owner is an SpotDetails instance. Or you could construct the view's contents in code in your override of viewDidLoad. The details are in the UIViewController documentation, or, even better, read my book which tells you all about how a view controller gets its view:
http://www.apeth.com/iOSBook/ch19.html
The reason this problem didn't arise before is that you drew the view in the same nib as the view controller (i.e. the storyboard file). But when you alloc-init a SpotDetails, that is not the same instance as the one in the storyboard file, so you don't get that view. Thus, one solution could be to load the storyboard and fetch that SpotDetails instance, the one in the storyboard (by calling instantiateViewControllerWithIdentifier:). I explain how to do that here:
http://www.apeth.com/iOSBook/ch19.html#SECsivc