I seem to be having some trouble finding the answer to this one.
My Application loads view controllers using this code:
World_Pick *world_pick = [[World_Pick alloc] initWithNibName:#"World Pick"
bundle:nil];
world_pick.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
[self presentModalViewController:world_pick animated:YES];
[world_pick release];
The problem is the previous view isnt being released from memory, and just adding on to it. I have tried stuff like
[self.view removeFromSubview];
[viewController release];
ViewController = nil;
None of which seem to work. Could someone help me?
Thanks
If I understand correctly what you mean, I would say that it is normal, when you present a view controller modally that the underlying view controller is not removed and the view remains there. This is how modal view controllers are presented asa far as I know.
I don´t know what UI you are trying to build into your app, but maybe you should look into using a UINavigationController or, possibly, just adding/removing your views to a base view as need arise. This is of course just a guess, I don´t know what you are trying to do but if you provide more detail, I can help further.
The view controller that's presenting world_pick, the one that's self in the code above, should probably be left alone -- it's presenting a modal view controller, after all, and you'll go back to that view controller when the modal controller is dismissed. The view that it manages should also be left alone. It may be unloaded if there's a memory warning, but if there's memory available it should remain so that it's in place when the modal view controller is dismissed.
Is there some reason you're concerned about this?
Related
Just for the purpose of learning some particular aspects of xCode, I am creating a simple app that has 2 functional view controllers. Each contains a button that can be pressed to switch to the other. I am not using segues. I am using pointers retrieved from the app delegate.
visual illustration (click for higher resolution):
When the app loads, the root view controller presents view 1. When you click "switch to view 2," the following code causes view 2 to appear:
- (IBAction)buttonPressed:(id)sender
{
AppDelegate *appDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
[self presentViewController:appDelegate.view2 animated:YES completion:nil];
}
So far, so good.
But when you click "switch to view 1" on the second view, this same code (replacing "view2" with "view1") gives the following error:
Application tried to present modally an active controller.
So to summarize (where --> = presents), we have root --> view1 --> view2 -x-> view1
I don't care about retaining the history of who presents whom. I simply want the buttons to bring to the top (make visible) a previously displayed view controller, maintaining the state of its views.
It would be nice to know the following:
Is there a workaround that would enable me to achieve the intended behavior using presentViewController? E.g., root --> view2 --> view1
What other method(s) would be more practical for achieving the desired behavior? It/they must use the app delegate because in my real application that will be unavoidable.
Am I breaking the rules by trying to put a view controller on top without integrating into some larger architecture? E.g, is this sort of behavior supposed to be handled by navigation conrollers and pushing/popping? If so, can you explain why xCode doesn't want me to do this? Why can't I just display whatever view controller I want, without it necessarily having any relationship to other view controllers? (Maybe because that could lead to abuse of the app delegate?)
What does it really mean to "present" a view controller? What functional limitations or capabilities does it entail beyond creating pointers between presenting and presenter? What is the importance of leaving the presenting view controller "active"?
If instead make the button on view1 send the presentViewController message to the root view (which I hoped would just change the presentation chain from root --> view1 to root --> view2, leaving view1 still existing in memory but not part of this chain), I get a different error: "Attempt to present on whose view is not in the window hierarchy!" What does this mean? I can't find an explanation of window hierarchy.
Okay, I know I'm asking a lot here, but any amount of enlightenment will be greatly appreciated!!
The correct way to do this is to get the underlying rootVC to do the presenting and dismissing (as you attempt - without the dismissing part - in point 5). You can achieve this by sending a message + completion block back to the rootVC from each of view1 and view2 when you want to present the other.
When you are in view1:
- (IBAction)buttonPressed:(id)sender
AppDelegate *appDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
UIViewController* presentingVC = self.presentingViewController;
[presentingVC dismissViewControllerAnimated:YES completion:^{
[presentingVC presentViewController:appDelegate.view2
animated:YES
completion:nil];
}];
}
and similarly for view2. Take care that you need this line:
UIViewController* presentingVC = self.presentingViewController;
as you can't refer to 'self.presentingViewController' inside the completion block as it's controller has been dismissed at this point.
I think that answers points 1 and 2.
To answer point 3 "Why can't I just display whatever view controller I want, without it necessarily having any relationship to other view controllers?" - well you can (via the rootViewController property of the window), but then you are going to have to implement navigation and manage your viewController pointers, which means you will end up creating a controller of some sort. Apple is helping you here by providing you with a few which cover most needs.
As regards your point 4 - the presenting of a viewController is controlled by the presenting VC, which is why you want to keep that one 'active'. When you send this message:
[self dismissViewControllerAnimated:completion:], self just reroutes the messge to it's presentingViewController. If you get rid of your presentingViewController your dismiss method will break.
Point 5 is answered above. You need to dismiss the topmost view first before asking an underlying view to present. Note that view1 is "still in memory" but only because you have retained a pointer to it in your app delegate.
update
As you are trying to get this to work with an initial launch-straight-to-view1, you could make a BOOL launched property and check/set it from your rootViewController's viewDidAppear:
- (void) viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
if (!self.launched) {
self.launched = TRUE;
AppDelegate *appDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
[self presentViewController:appDelegate.view1
animated:YES
completion:nil];
}
}
Let me try to tackle your points one by one.
1) No, you shouldn't do this all with presentViewController.
2) If you want to do root --> view1 --> view2 --> view1, then you don't do that all with presentViewController. To go from view1 back to view2 you should use dismissViewControllerAnimated:completion.
3) The view controllers do have a relationship when you use presentViewController:animated:. The presenting controller has a pointer to the one it presents, and the presented one has a pointer to the one that presented it. So, you're getting these relationships whether you want it or not. There is a way to display whatever controller you want with no relationship between them -- just reset the window's root view controller. The old view controller will be deallocated (if you don't keep a strong pointer to it), and the new one becomes the window's root view controller.
4) Presenting a view controller makes that controller a modal view controller -- it takes over the whole screen and is intended to be used as an interruption in the flow of the app. You really shouldn't use them extensively to go from one controller to another (and especially not for going "backwards" to previous controllers). Because of the way it's supposed to be used, you normally want to go back to the controller that presented it, so that's why it's kept "active" (in the sense that it's not deallocated).
5) You get that error because root's view is not on screen, view1's is. You need to present a view controller from the controller on screen.
For my app, I want to have a few different instances of the same view controller. For now, I am just creating a new instance like this:
iSafeViewController *tab = [[iSafeViewController alloc] init];
[tab setModalPresentationStyle:UIModalPresentationFullScreen];
[tab setModalTransitionStyle:UIModalTransitionStyleCrossDissolve];
[self presentViewController:tab animated:YES completion:nil];
Great. And since this is done in the iSafeViewController class anyway, I have another button that currently just dismisses the latest controller on the stack.
- (IBAction)closeTab:(id)sender {
[self dismissViewControllerAnimated:YES completion:nil];
}
Okay, however, I really want to be able to go back to these instances. So, I have two questions.
Does dismissViewControllerAnimated remove that controller's instance from memory. If not, is there a way I can re-present it.
There is probably a better way to navigate through viewController instances then presentViewControllerAnimated. At the very least, is there a better way to create new instances of one's viewController and be able to navigate to each of them, hopefully not in a stack. In other words, if there are three viewController instances, is there a way I can go from the third to the main one?
Any ideas would be appreciated. Thanks.
"Does dismissViewControllerAnimated remove that controller's instance from memory? If not, is there a way I can re-present it."
Calling dismissViewControllerAnimated does not explicitly remove a view controller from memory, but if no other part of the code is storing a strong reference to the view controller, once the presenting view controller dismisses your VC, it may be deallocated as per the normal memory management system.
So if you ensure something in your code has a reference to your view controller (aside from the VC which is presenting it modally), it won't disappear after being dismissed, and yes this means you can re-use it.
As for "random access" to view controllers: you could use UINavigationController and use methods like popToViewController:animated: and multiple calls to pushViewController:animated: (without animation!) to create the effect of travelling to arbitrary view controllers. This feels like a bit of a hack.
Alternatively, and preferably, you could write your own custom container view controller. This is a view controller that deals with presenting other view controllers. See Apple docs.
Here's a good WWDC video on the subject: Implementing UIViewController Containment
Further reading:
Container View Controller Examples
http://subjective-objective-c.blogspot.co.uk/2011/08/writing-high-quality-view-controller.html
Custom container view controller
I'm a new iOS developer with a simple question: I want to programmatically move from one view controller to the next, how do I write this code?
So far I have:
UINavigationController *navigationController;
navigationController = [[UINavigationController alloc] init];
[self.view addSubview:navigationController.view];
[navigationController pushViewController:viewController animated:NO];
I'm not even sure if this will work, ultimately, but my main question is "viewController" in line 4. The program doesn't know what that is. It is the name of my current view controller, but how do I set it up so that it knows what I mean by viewController?
As an aside, the above is part of an if/else statement that occurs and is connected to the NSUserDefaults class to make it such that the view controller I am referring to only loads if terms and conditions have not previously been accepted. Will that work? Thanks.
First the simple answer: pass self when you want to pass the "current" object.
The more important consideration is: is that nav controller on screen? It's likely that your code won't do much unless you use a navigation controller which is (probably) the window's root view controller.
This is fairly easy to setup in your storyboard ("embed in"->"navigation controller") and then you don't need to instantiate it in code, you simply use self.navigationController (usually).
Normally, you would instantiate viewController just before you push it, so the program will know what it is. And, sure, you can have an if statement, and push this new view controller based on how the if statement evaluates.
I'm not sure about the code you wrote -- whether that's right depends on the structure of your app, and where you're doing this. Often, the navigation controller is made the root view controller of the window, and you set the navigation controller with a root view controller of its own when you create it
I decided to give the use of storyboards a go in my current iPhone app. I am facing a bit of a problem. I really need to reuse my UIViewController instances.
What do I mean by that? Well, for example I have a table view controller. When I tap a cell, another view controller is loaded from the storyboard and pushed onto the navigation controller stack. This all works well, but it takes about half a second to a second each time this view controller is loaded. Before I was using story boards I simply solved this problem by caching the created instance so the second time you tap a cell the view controller can be immediately shown.
By caching the created instance I mean something like this:
if (!cachedInstance) {
cachedInstance = [MyViewController new];
}
[self.navigationController pushViewController:cachedInstance];
Does anyone know how to accomplish this using the storyboard? Thanks in advance.
If you are using segues, you will need to create custom segues in order to use a cached view controller like you did before. Otherwise, the typical "push" segue will create a new instance of the view controller for segue.destinationViewController. If you write a custom UIStoryboardSegue class and use custom segues you can override initWithIdentifier:source:destination: and put your cached view controller in for the destinationViewController, and then override perform to use the classic pushViewController call.
That is how you handle the segue if you are really intent on using them. I would just skip it though, unless you really want the fancy arrows to lay everything out on your storyboard. If you skip it you can just instantiate the view controllers into the cache and then push them on just like you did before.
If your question is more about locating a view controller inside a storyboard then you can use:
UIViewController *vc = [[UIStoryboard storyboardWithName:#"MainStoryboard" bundle:nil] instantiateViewControllerWithIdentifier:#"Some View Controller"];
Then you can save that to your cache and push it like you did in your example code.
Hope that helps.
So I have a viewControllerA, and I want to add another View managed by viewControllerB to it. There is only one UISlider activating a simple action in viewControllerB. It won't crash if I don't touch this UISlider, it will once I use UISlider. I am using ARC. I am using:
[self.view addSubView: viewControllerB.view];
to add viewControllerB to viewControllerA. Am I missing something? Thanks.
OK. It looks like a really simple situation. I just added one view controller and one action. Here is the demo project code on github: https://github.com/randomor/Demo
The reason why I want this to work is because I have another app that will create a view controller on the spot and add it to anther view. And I don't want to do it modally, because I don't want the new view controller to cover the whole screen. Thanks.
SOLUTION: So I'm now just using the latest ViewController containment API:
[self addChildViewController:viewControllerB];
It works! as long as I added this line, the event will be passed to its own controller and it stopped crashing.
i recommend you, to use the following code
in ViewControllerA.h
#import "ViewControllerB.h"
in ViewControllerA.m (where you want to push the new controller)
ViewControllerB *newController = [[ViewControllerB alloc]init];
[self presentModalViewController:newController animated:YES];
in ViewControllerB.m you will need
[self.presentingViewController dismissModalViewControllerAnimated:YES];
to make it vanish again.
concerning multiple controllers for one open screen (Apple ViewController Programming Guide):
Each custom view controller object you create is responsible for managing exactly
one screen’s worth of content. The one-to-one correspondence between a view controller
and a screen is a very important consideration in the design of your application.
You should not use multiple custom view controllers to manage different portions
of the same screen. Similarly, you should not use a single custom view controller
object to manage multiple screens worth of content.
You should try and avoid the practice of nesting UIViewControllers. While it is technically supported in iOS5, it is ill-advised, for many reasons, including the type of problem that you're having (you have a dangling pointer to a UIViewController, which is why you are crashing).
http://blog.carbonfive.com/2011/03/09/abusing-uiviewcontrollers/
Although this question is extremely vague, I imagine that you are not keeping a reference to View Controller B, and so when view B tries to interact with it, it causes EXC_BAD_ACCESS.
What's the object that is set as the target for the slider? If it's a EXC_BAD_ADDRESS, then you may not be retaining the target, most probably the view controller for the slider.