I am using storyboard and i stumbled upon something i have not been able to grasp.
I am putting up my view controller programmatically with performSegueWithIdentifier:.
It works like a charm, but what i noticed was that every single time i do this, i create a new instance of that viewController, and so, i have memory that keeps piling up. When i simulate a memory warning, i see that for each time i have been calling performSegueWithIdentifier:
i have a new instance of the view controller, and it NEVER gets deallocated. So memory just piles up and i cannot release it, which eventually causes a crash.
I just go to the view controller like this:
// If sales are registered, go to view
[self performSegueWithIdentifier:#"previousSaleSegue" sender:self];
What am i missing here?
You'll be stacking view controllers on top of each other instead of returning to a previous one. Assuming you are using a navigation controller, you'll be doing this:
A --push--> B --finished! Push---> New A ---Push---> B ---Finished! push--->A ...
What you should be doing is:
A --push--> B --finished! Pop -
^-----------------------------/
You're using modal segues by your comments, in this case you need to add an action to your return button to dismiss the view controller (returning to the previous one) instead of presenting another instance. The principle is the same. You'd use
[self dismissViewControllerAnimated:YES completion:nil];
If you're certain that viewcontroller instance does not get deallocated it must be because you keep reference to it somewhere (it could be a cycle on the controller itself).
Related
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 am working on an IPhone app that, through viewDidLoad, makes a connection and pulls data into a table. I would like the controller, or at least the table, to reload every time the controller is displayed, even if someone just switched from one tab to another or closed and re-opened the app on this controller. Is there a way to do this? I can't seem to find anything, it's also kind of a hard thing to search for. I have found discussions of when to put code in viewDidLoad but not another method that is run every them the controller displays.
Thanks,
Cheryl
You want to use
-(void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
//code to reload table viewdata
}
Each time the view appears this method is called. I use this a lot in my app.
There's no way to do it by injecting code in only one place.
You can think of a workaround, like for example sending custom "reload request" notification from required parts of code:
viewDidAppear: in your view controller
applicationDidBecomeActive: (if table is presented)
tabBarController:didSelectViewController: (if switched onto controller with the table)
tabBar:didSelectItem: (same as above)
etc.
In you view controller simply observe this notification and reload data when required.
Although, whats more important: do you really need to reload data under such harsh requirements? In most cases data reload happens when
view controller's viewDidLoad: is called
it is manually initiated (button, for example)
long time passed since the last update was received
Otherwise it's just an overkill.
I'm using a UINavigationController to navigate between classes. When I press a button on the first view to send me to the second one, everythin works fine. But when I wan't to return from the second, to the first view, the viewDidLoad method isn't being called, and I really need that to happen.
According to this post, I should somehow set my view to nil but I'm not sure where or how to do that. This is the code that I'm using to return to the first view:
NewSongController *nsContr = [[NewSongController alloc] initWithNibName:#"mNSController" bundle:nil];
[self.navigationController popViewControllerAnimated:YES];
[nsContr release];
Your code is not correct.
You don't need to instantiate your first controller in order to pop to it. It already exists.
viewDidLoad will only run when you load the viewController for the first time (i.e. when you push to it). When you push to other controllers they are put onto a stack (imagine a stack of cards). When you push another card onto the stack the cards beneath it are already there.
When you pop it is like removing a card from the stack. But the card underneath is already there so it doesn't need to load again. All it does is run viewWillAppear.
All you need to do to pop back is...
[self.navigationController popViewControllerAnimated:YES];
That's it.
Remove the stuff about NewSongController (if that is what you are trying to go back to).
Then in the NewSongController function - (void)viewWillAppear:animated; put the code you want to run when you get back to it.
Hope that helps.
Your first view is loaded and is pushed onto the navigation stack. Dont try to mess with whats on the stack without fully understanding how setting the view to nil will affect the behavior.
Whatever you do on viewDidLoad, doing it in viewWillAppear or viewDidAppear will give you the result you want.
The viewDidLoad wouldn't appear because it already exists in the navigation stack. Since you are going back in the stack you would want to have the code that you want to trigger in viewWillAppear or viewDidAppear which is executed when popping from one viewcontroller to the one below it.
I have an app which is based on a UINavigationController. There is a menu screen with buttons that segue (push onto navigation controller stack) to one of 9 other "sub-screens". None of these sub-screens segue to any other screen. When a user is done inputing data on a "sub-screen" they can press a done button which will pop back to the original menu screen. (If you're having difficulty picturing this, imagine a tree like storyboard where there is one root ViewController and then 9 leaf viewControllers).
Ok, so with that setup I have a few questions about how viewDidLoad works.
~ First, is viewDidLoad supposed to be called every time we transition to a sub-screen. For example, suppose I go from the menu screen to sub-screen "B", back to the menu screen and then back to sub-screen "B". Should B's viewDidLoad method be called twice? If not, why might mine be getting called twice?
~ Second, assuming that it will get called each time, what do I do if I have a lot of long operations that need to be performed exactly one time for each sub-screen? Where should I put them (if I put them in viewDidLoad it would happen multiple times if the user kept going back and forth between this page and the menu)?
To answer your questions:
Yes, in general B's viewDidLoad method should be called each time that it is pushed onto the UINavigationController's stack. This is because each time that B is popped off of the stack it is typically released, and each time that you go to B a new instance of B is created.
There could be numerous ways to handle this type of situation. It is hard to tell what is right for you without seeing exactly what you are trying to do. One way would be to create a singleton object that handles the processing. The reason this might be better than handling it within your UIViewController is that a singleton can live throughout the lifetime of the application, whereas UIViewControllers typically have a relatively short lifespan. Singleton objects can be created just once and they can manage whatever operations and data that you need to persist through the lifetime of your application.
1.
viewDidLoad is called when the view is loaded, and viewWillAppear is called when the view becomes visible.
If your viewDidLoad is called several times that means that you are loading the view every time you are showing it and releasing it every time you are popping it. If you post some code I could help you identify the problem better.
What you could do is something like this:
In your "root" viewController class, declare each "leaf" ViewController as a member, lets say they are called leafController1, leafController2 etc and create retain-properties for them.
#interface YourRootViewController : UIViewController {
LeafController1Class *leafController1;
LeafController2Class *leafController2;
// ...
}
#property (nonatomic, retain) LeafController1Class *leafController1;
#property (nonatomic, retain) LeafController2Class *leafController2;
// ...
#end
In the ViewDidLoad of your top ViewController, init all the leaf-controllers using "initWithNibName" etc (or whatever you are doing to create them). Retain their instances like so:
self.leafController1 = [[[LeafController1Class alloc] initWithNibName:#"LeafController1NibName" bundle:nil] autorelease];
When the user presses a button, push the correct leaf to the navigationcontroller:
[myNavigationController pushViewController:leafController1 animated:YES];
When you pop the leaf controllers now, they will be kept in memory since you retained them.
This way your viewDidLoad will only be called once for each leaf, just as long as you always push the same instace of the viewcontroller to your navigationcontroller.
2.
Heavy code related to the view should be executed when the view has been loaded, i.e. triggered by viewDidLoad. But also it might be a good idea to keep other classes that hold info about your application which are not viewcontrollers and separate from the UI. Heavy computations is better made in the background, or when the app is loading for the first time.
viewWillAppear gets called every time the view appears. viewDidLoad ONLY gets called when the view is constructed - so for example after a view controller initFromNibNamed call when the view is accessed. viewWillAppear is called anytime your view controller was not in view but comes into view - so when your view controller is pushed, viewWillAppear is called. So you might think your viewDidLoad is being called twice, but in reality it's probably not. So you should put the methods in viewDidLoad. What are you doing that takes a long time?
I have created a tabBarNavigated Application. In second tab, I do something that works fine, but now I want to do something in the first Tab, so first I try to NSLog a string, but I get no reaction.
- (void)viewDidLoad
{
NSLog(#"Test");
}
If I add a label to the view, it will be displayed, but no reaction on my code.
if I start my app, i see this view, but i can't call any actions in this method, even if i change the tab, and go back to the first one, still no logs.
I try to NSlog in GehaltView
this is the mainWindow
viewWillAppear dosn't work :(
The -viewDidLoad method is only called when your view is loaded. This method will not be called again unless the view gets unloaded, in which case -viewDidUnload will be called. A view can be unloaded if there is a memory issue, but otherwise they generally stick around.
If you want to trigger an action that happens every time the view appears, then you can use the -viewWillAppear: method instead. This method is called every time the view re-appears. You can track when the view disappears with -viewWillDisappear, and watch the two get called as you toggle between the two tabs.
Note also that -viewDidLoad may get called before the view appears, but -viewWillAppear will only be called when the view actually appears (or moments before, as the will indicates).
EDIT: The code should read
-(void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
NSLog(#"View Will Appear");
}
EDIT: This entire answer assumes that you have a subclass of UIViewController. It seems to me that you are by-passing using viewControllers, which in general is a bad idea.
I found the solution, in interface builder i have to add a custom class to the forst tab.