I am developing an app that is a single NSWindow and clicking a button inside the window will present a NSViewController, and a button exists in that controller that will present a different NSViewController. I know how to swap out views in the window, but I ran into an issue trying to do this with the multiple view controllers. I have resolved the issue, but I don't believe I am accomplishing this behavior in an appropriate way.
I originally defined a method in the AppDelegate:
- (void)displayViewcontroller:(NSViewController *)viewController {
BOOL ended = [self.window makeFirstResponder:self.window];
if (!ended) {
NSBeep();
return;
}
[self.box setContentView:viewController.view];
}
I set up a target/action for an NSButton to the AppDelegate, and here's where I call that method to show a new view controller:
- (IBAction)didTapContinue:(NSButton *)sender {
NewViewController *newVC = [[NewViewController alloc] init];
[self displayViewcontroller:newVC];
}
This does work - it presents the new view controller's view. However if I then click any button in that view that has a target/action set up that resides within its view controller class, the app instantly crashes.
To resolve this issue, I have to change didTapContinue: to the following:
- (IBAction)didTapContinue:(NSButton *)sender {
NewViewController *newVC = [[NewViewController alloc] init];
[self.viewControllers addObject:newVC];
[self displayViewcontroller:[self.viewControllers lastObject]];
}
First of all, can you explain why that resolves the issue? Seems to be related to the way the controller is "held onto" in memory but I'm not positive.
My question is, how do I set this up so that I can swap out views from within any view controller? I was planning on getting a reference to the AppDelegate and calling displayViewcontroller: with a new controller I just instantiated in that class, but this causes the crash. I need to first store it in the array then send that reference into the method. Is that a valid approach - make the viewControllers array public then call that method with the lastObject, or how should this be set up?
What is interesting in your code is that you alloc/init a new view controller every time that you call the IBAction. It can be that your view its totally new every time you call the IBAction method, but I would think that you only have a limited number of views you want to show. As far as my knowledge goes this makes your view only to live as long as your IBAction method is long. That the view still exists, is because you haven't refreshed it. However, calling a method inside a view controller that is not in the heap anymore (since you left the IBAction method and all local objects, such as your view controller are taken of the heap thans to ARC) makes the app crash, because you reference a memory space that is not in use or used by something else.
Why does the app work when you ad the view to the viewcontrollers array? I assume this array is an array that has been initiated in the AppDelegate and now you add the view controller with a strong reference count to the viewcontrollers array. When you leave the IBAction method, the view controller still has a strong reference and ARC will not deallocate the view controller.
Is this the proper way? Well, it works. I would not think it is considered very good programming, since you don't alloc/init an object in a method that needs to stay alive after leaving the method. It would be better practice to allocate and initialize your view controller(s) somewhere in an init, awakeFromNIB or a windowDidLoad method of your AppDelegate. The problem with your current solution is that you are creating an endless array of view controllers of which you only use the last. Somewhere your program will feel the burden of this enormously long array of pretty heavy objects (view controllers) and will run out of memory.
Hope this helps.
By the way, this is independent of whether you use Mavericks or Yosemite. I was thinking in a storyboard solution, but that wouldn't answer your question.
Kind regards,
MacUserT
I am new to osx developing I have read on documentations about windowDidResized:
method , but I am failing to get its delegate .
It is never get called for me , I have included appKit/appKit.h as it said in docs
but the delegate method never triggers
(I am trying to get it inside my NSViewController)
can some one please make a simple example how do i get that delegate please?
what I have tried to do is:
-(void)loadView
{
//blabla
self.view.window.delegate = [self.view.window delegate];
//blabla ..
}
- (void)windowDidResize:(NSNotification *)notification
{
NSLog(#"window Resized");
}
I am expecting non xib usage samples please :)
thanks a lot in advance.
A view probably shouldn't be a window's delegate.
Normally the delegate for a window would be a controller object in the Model View Controller paradigm.
You can however use NSNotificationCenter to add an object as an observer for a specific NSNotification from a specific object.
( be sure to remove the observer in its dealloc method if not earlier )
NSWindow class sends many different notifications.
Ok, here is the deal, I hate putting out questions about my debugging and crashes. Because I usually handle them myself, but I just cannot get my way around this, even after viewing multiple questions already.
Ok so here is the problem, I find my app randomly on and off crashing with this stack trace:
*** -[ViewController respondsToSelector:]: message sent to deallocated instance 0x1e5d2ef0
Where ViewController can vary, sometimes the place where my code crashes, has NO relevance to that particular ViewController and doesn't own or call it.
Also, to get that console trace, I have enabled Zombies, otherwise I would get no console print at all, I would only get: objc_msgSend, which I know means I am messaging something that is released. But I cannot find where that is... I am really stuck! Usually I always debug my crashes, so I am really stuck on this.
Again, this crashes in different places at different times, on and off. And the place it crashes has almost no relevance to the ViewController. And I find this very confusing.
Do you need any of my code? I have a lot of files and since it is crashing in different places, distributing my code will be a mess!
I have tried to add symbolic breakpoints with no luck, and Zombies is not available on the Instruments application for iOS. I cannot run my app on the simulator as it has unsupportive architecture frameworks for it.
Thanks everyone...
Use Instruments to track down deallocated instance errors. Profile your application (Cmd ⌘+I) and choose Zombies template. After your application is running, try to crash it. You should get something like that:
Click on the arrow next to address in the popover to show object that was called after it was deallocated.
You should see now every call that has changed retain count of this object. This could be because sending directly retain/release messages as well as draining autorelease pools or inserting into NSArrays.
RefCt column shows retainCount after action was invoked and Responsible Caller shows class name and method in which it was performed. When you double click on any retain/release, instruments will show you line of code where this was performed (If this isn't working, you can examine call by selecting it and choosing its counterpart in Extended Detail pane):
This will let you examine all the retainCount lifecycle of object and probably you'll find your problem right away. All you got to do is find missing retain for latest release.
had a similar problem. In my case a viewController needed to get navigationController events, so it was registering as the navigation controller delegate:
self.navigationController.delegate = self;
The crash occurs when that controller was dealloc'ed but was still the delegate for the view controller. Adding this code in dealloc had no effect:
-(void) dealloc
{
if (self.navigationController.delegate == self)
{
self.navigationController.delegate = nil;
}
because at the point that dealloc is called, the view controller has already been removed from the view hierarchy, so self.navigationController is nil, so the comparison is guaranteed to fail! :-(
The solution was to add this code to detect the VC leaving the view hierarchy just before it actually does so. It uses a method introduced in iOS 5 to determine when the view is being pop'ed and not pushed
-(void) viewWillDisappear:(BOOL) animated
{
[super viewWillDisappear:animated];
if ([self isMovingFromParentViewController])
{
if (self.navigationController.delegate == self)
{
self.navigationController.delegate = nil;
}
}
}
No more crashes!
For anyone who can't solve it, here are some other techniques:
https://stackoverflow.com/a/12264647/539149
https://stackoverflow.com/a/5698635/539149
https://stackoverflow.com/a/9359792/539149
https://stackoverflow.com/a/15270549/539149
https://stackoverflow.com/a/12098735/539149
You can run Instruments in Xcode 5 by clicking the project popup->Edit Scheme...Profile ->Instrument and choose Allocations or Leaks, then profile your app, then stop Instruments, click the info button in Allocations and "Enable NSZombie Detection".
However, for the messages that come directly from the com.apple.main-thread, this probably won't reveal anything.
I banged my head on this for over two hours and the answer turned out to be an over-release, which I discovered by commenting out a copy of my project by brute force until I found the culprit:
[viewController release];
viewController = NULL;
The problem is that release doesn't set the variable to NULL.
That means that setting it to NULL calls release again, decrementing the refcount and freeing the memory immediately until later when the variables that reference viewController are finished with it.
So either enable ARC or make sure your project consistently uses release or NULL but not both. My preference is to use NULL because then there is no chance of referencing a zombie but it makes finding where objects are released more difficult.
I had met the same problem in iOS yesterday. I have made IAP in App "About" subview, and I have added Transaction Observer in "About" viewDidLoad. When I purchase for the first time, no problem, but after I back to main window and enter about subview to purchase again, the problem "message sent to deallocated instance" happened, and the App crashed.
- (void)viewDidLoad
{
[[SKPaymentQueue defaultQueue] addTransactionObserver:self]; object:nil];
}
After I remove Transaction Observer in dealloc, the problem is solved.
- (void)dealloc
{
// Even though we are using ARC, we still need to manually stop observing any
// NSNotificationCenter notifications. Otherwise we could get "zombie" crashes when
// NSNotificationCenter tries to notify us after our -dealloc finished.
[[SKPaymentQueue defaultQueue] removeTransactionObserver:self];
}
I had a very similar issue and I figured out it was due to navigation controller delegates set.
The below solved my issue,
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
if (self.navigationController.delegate != self) {
self.navigationController.delegate = self;
}
}
-(void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
if (self.navigationController.delegate == self) {
self.navigationController.delegate = nil;
}
}
Had the same problem in OS X.
To solve this not enough - (void)dealloc method as #SoftwareEvolved already said. But unfortunately - (void)viewWillDisappear is available only on version 10.10 and later.
I introduced custom method in my NSViewController subclass where set all the zombie-dangerous references to nil. In my case that was NSTableView properties (delegate and dataSource).
- (void)shutdown
{
self.tableView.delegate = nil;
self.tableView.dataSource = nil;
}
That's all. Each time I'm about to remove view from the superview need call this method.
I had the same Problem.It was difficult to find which delegate cause issue, because it does not indicate any line or code statement So I have try some way, Maybe it becomes helpful to you.
Open xib file and from file's owner, Select "show the connections inspector" right hand side menu. Delegates are listed, set them to nil which are suspected.
(Same as my case)Property Object like Textfield can create issue, So set its delegates to nil.
-(void) viewWillDisappear:(BOOL) animated{
[super viewWillDisappear:animated];
if ([self isMovingFromParentViewController]){
self.countryTextField.delegate = nil;
self.stateTextField.delegate = nil;
}
}
i used this delegate to avoid dismissing of my UIPopover controller from my View.
-(BOOL)popoverControllerShouldDismissPopover:(UIPopoverController *)popoverController
{
return NO;
}
there is a problem i am facing with these delegate .
i cant able to do any actions or any process in my View after i implemented this delegate.
so i am troubling with this problem .how can i avoid this problem with displaying my UIpopover.can any one tell me please.....
Have you assigned your view to the passThroughViews property? It's in the documentation
This should be straight forward for a guru. I don't have any code really written out, just a couple of controllers and a custom UIView. All connected through nibs. The app loads without crashing, yet I can't see my NSLog() hit from my custom UIView.
My application delegate has default template code which calls for a class of mine called TabAnimationController. TabAnimationViewController has its view set to TabView. I made sure that in TabAnimationViewController's NIB that File's owner is set to TabAnimationViewController and that my instance of UIView has its class set to TabView.
In TabView.m I'm trying to see how NSLog is going to hit, and it's not showing up at all.
- (void)loadView {
NSLog(#"calling loadView");
}
- (id)initWithFrame:(CGRect)frame {
NSLog(#"Calling initWithFrame:");
return self;
}
Strange. I'm not sure why even after proper IB connections that my NSLog will not show up. Only anything put into drawRect: will invoke. Why isn't initWithFrame or loadView ever get hit? What if I want to customize this view programmatically?
First of all, when a view is dehydrated from nib file, instead of initWithFrame, initWithCoder is invoked. So you need to implement your initialization in initWithCoder as well. (It may be a good idea to keep the initWithFrame initialization as well, if you anticipate programmatically creating your TabView instead of hooking up in the IB. Just refactor your initialization to another method and call it from both implementations.)
Also in your initialization code above you must always call the super class's initialization. There is a boiler plate pattern all custom classes use in their init implementation for that:
if (self = [super initXXX]) { do your initialization }
return self;
Second, loadView which is actually a UIViewController method and not a UIView method is invoked only if the view outlet of the controller is nil.
Unless you are composing your view yourself programmatically using your controller, you do not need to override loadView. Instead you should override viewDidLoad, which is called after the view is loaded, to do additional initialization.
The simplest way to get this up and running is simply to use the "View based Application" template when you create a new project. It sets up everything you need to start with.
But, in short, you're looking at the wrong methods. First, you shouldn't override loadView unless you're creating your view programatically. If it's loading from a XIB file look at the initWithNibName method.
You might also want to look at the viewDidLoad, viewWillAppear and viewDidAppear methods that are triggered, well, it's fairly obvious when!