Ok, I'm having a lot of problems right now trying to get initWithCoder: to work right. I have a nib file that gets loaded, and in my app delegate, I call unarchiveWithFile: for the view controller that is associated with that nib, and now my app crashes. I can see that initWithCoder: is being called twice, presumably once from when awakeFromNib: is called, and then from when I call unarchiveWithFile: since the view controller conforms to NSCoding. But now either it crashes as soon as the view loads or when I press an IBOutlet. Any suggestions??
Edit: Here's the code for initWithCoder:
- (id)initWithCoder:(NSCoder *)coder {
[super initWithCoder:coder];
[[self mapView] addAnnotations:[[coder decodeObjectForKey:#"Annotations"] retain]];
return self;
}
All I'm doing is decoding an array of annotations for a map view, but somewhere along the line this method is being called twice and then it crashes.
Don't forget to put the nil check in your init methods. E.g. the method you posted would be more correct if you wrote it as:
- (id)initWithCoder:(NSCoder *)coder {
if (self = [super initWithCoder:coder]) {
[[self mapView] addAnnotations:[[coder decodeObjectForKey:#"Annotations"] retain]];
}
return self;
}
That's not the cause of your problem, however.
Is there are good reason for you unarchiving your view controller yourself? If you're not doing anything special, you can rely on the existing mechanisms to do it. The default implementation of init for a UIViewController looks for a nib with the same name as your view controller, and if it exists, it loads the nib (via initWithNibName).
If there is data which you need to archive in and out, it may be that it shouldn't be actually part of the UIViewController. Factor it out elsewhere perhaps?
you can try
- (id)initWithCoder:(NSCoder *)coder {
if(self == nil)
{
[super initWithCoder:coder];
[[self mapView] addAnnotations:[[coder decodeObjectForKey:#"Annotations"] retain]];
}
return self;
}
Related
I want to check the pasteboard and show an alert if it contains specific values when the view appears. I can place the code into viewDidLoad to ensure it's only invoked once, but the problem is that the alert view shows too quickly. I know I can set a timer to defer the alert's appearance, but it's not a good work-around I think.
I checked the question iOS 7 - Difference between viewDidLoad and viewDidAppear and found that there is one step for checking whether the view exists. So I wonder if there's any api for doing this?
Update: The "only once" means the lifetime of the view controller instance.
There is a standard, built-in method you can use for this.
Objective-C:
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
if ([self isBeingPresented] || [self isMovingToParentViewController]) {
// Perform an action that will only be done once
}
}
Swift 3:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
if self.isBeingPresented || self.isMovingToParentViewController {
// Perform an action that will only be done once
}
}
The call to isBeingPresented is true when a view controller is first being shown as a result of being shown modally. isMovingToParentViewController is true when a view controller is first being pushed onto the navigation stack. One of the two will be true the first time the view controller appears.
No need to deal with BOOL ivars or any other trick to track the first call.
rmaddy's answers is really good but it does not solve the problem when the view controller is the root view controller of a navigation controller and all other containers that do not pass these flags to its child view controller.
So such situations i find best to use a flag and consume it later on.
#interface SomeViewController()
{
BOOL isfirstAppeareanceExecutionDone;
}
#end
#implementation SomeViewController
-(void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
if(isfirstAppeareanceExecutionDone == NO) {
// Do your stuff
isfirstAppeareanceExecutionDone = YES;
}
}
#end
If I understand your question correctly, you can simply set a BOOL variable to recognize that viewDidAppear has already been called, ex:
- (void)viewDidAppear {
if (!self.viewHasBeenSet) { // <-- BOOL default value equals NO
// Perform whatever code you'd like to perform
// the first time viewDidAppear is called
self.viewHasBeenSet = YES;
}
}
This solution will call viewDidAppear only once throughout the life cycle of the app even if you create the multiple object of the view controller this won't be called after one time. Please refer to the rmaddy's answer above
You can either perform selector in viewDidLoad or you can use dispatch_once_t in you viewDidAppear. If you find a better solution then please do share with me. This is how I do the stuff.
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelector:#selector(myMethod) withObject:nil afterDelay:2.0];
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
static dispatch_once_t once;
dispatch_once(&once, ^{
//your stuff
[self myMethod];
});
}
By reading other comments (and based on #rmaddy 's answer), I know this is not what OP asked for, but for those who come here because of title of the question:
extension UIViewController {
var isPresentingForFirstTime: Bool {
return isBeingPresented() || isMovingToParentViewController()
}
}
UPDATE
You should use this method in viewDidAppear and viewWillAppear. (thanks to #rmaddy)
UPDATE 2
This method only works with modally presented view controllers and pushed view controllers. it's not working with a childViewController. using didMoveToParentViewController would be better with childViewControllers.
You shouldn't have issues in nested view controllers with this check
extension UIViewController {
var isPresentingForFirstTime: Bool {
if let parent = parent {
return parent.isPresentingForFirstTime
}
return isBeingPresented || isMovingFromParent
}
}
Try to set a BOOL value, when the situation happens call it.
#interface AViewController : UIViewController
#property(nonatomic) BOOL doSomeStuff;
#end
#implementation AViewController
- (void) viewWillAppear:(BOOL)animated
{
if(doSomeStuff)
{
[self doSomeStuff];
doSomeStuff = NO;
}
}
in somewhere you init AViewController instance:
AddEventViewController *ad = [AddEventViewController new];
ad.doSomeStuff = YES;
Not sure why you do this in ViewDidAppear? But if you want doSomeStuff is private and soSomeStuff was called only once, here is another solution by notification:
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(doSomeStuff) name:#"do_some_stuff" object:nil];
- (void) doSomeStuff
{}
Then post when somewhere:
[[NSNotificationCenter defaultCenter] postNotificationName:#"do_some_stuff" object:nil];
swift 5
I've tried isBeingPresented() or isMovingToParent.
But It doesn't work.
So I tried below code. and It's work for me!
override func viewDidAppear(_ animated: Bool) {
if (self.isViewLoaded) {
// run only once
}
}
You can use this function in ViewDidLoad method
performSelector:withObject:afterDelay:
it will call that function after delay. so you don't have to use any custom timer object.
and For once you can use
dispatch_once DCD block.Just performSelector in the dispatch_once block it will call performSelector only once when ViewDidLoad is called
Hope it helps
I have set up a utility application and I found that the init method of MainViewController is not called automatically. Is there some other method that is set up automatically by XCode for initialization? Or if I have to add it, where would I add it? I was just going to call init manually from an IBOutlet method but I would prefer that the initializations be done when the view is first initialized.
Not sure where you'r going but (generated) .xib files are called using the withCoder init.
- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super initWithCoder:aDecoder];
if (self)
{
//self implementation
}
return self;
}
See the Utility Template in Xcode.
And check this method called..
- (IBAction)done:(id)sender
{
[self.delegate flipsideViewControllerDidFinish:self];
}
check it..
I'm relatively new to Objective-C and coding. I've tried doing a little dev on my own but have now become stuck on what is probably a rookie error.
I've created a tab bar controller with 5 views, one such view is a UIWebView. I've got the Webview working and it loads, but when I select a different tab, the app crashes. Please find my code below and any help would be appreciated!
#import <UIKit/UIKit.h>
#interface LiveViewController : UIViewController {
IBOutlet UIWebView *liveView;
}
#property (nonatomic, retain) UIWebView *liveView;
#end
#import "LiveViewController.h"
#implementation LiveViewController
#synthesize liveView;
// The designated initializer. Override if you create the controller programmatically and want to perform customization that is not appropriate for viewDidLoad.
/*
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization.
}
return self;
}
*/
/*
// Implement loadView to create a view hierarchy programmatically, without using a nib.
- (void)loadView {
}
*/
// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
[self.liveView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:#"http://www.britishseapower.co.uk/live/"]]];
[super viewDidLoad];
}
- (void)webViewDidStartLoad:(UIWebView *)liveView
{
// starting the load, show the activity indicator in the status bar
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
}
- (void)webViewDidFinishLoad:(UIWebView *)liveView
{
// finished loading, hide the activity indicator in the status bar
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}
- (void)liveView:(UIWebView *)liveView didFailLoadWithError:(NSError *)error
{
// load error, hide the activity indicator in the status bar
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
// report the error inside the webview
NSString* errorString = [NSString stringWithFormat:
#"<html><center><font size=+5 color='red'>An error occurred:<br>%#</font></center></html>",
error.localizedDescription];
[self.liveView loadHTMLString:errorString baseURL:nil];
}
- (void)viewWillDisappear:(BOOL)animated
{
if ( [self.liveView loading] ) {
[self.liveView stopLoading];
}
self.liveView.delegate = nil; // disconnect the delegate as the webview is hidden
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}
- (void)dealloc {
[liveView release];
[UIWebView release];
[LiveViewController release];
[super dealloc];
}
#end
Many thanks,
Ryan
[UIWebView release]; [LiveViewController release];
This is what make your app crash.
It's not valid to send a release message to a class itself.
What you've done with [liveView release]; is enough (with the call to [super dealloc];.)
You should also set the delegate to nil in the dealloc method as in the viewWillDisappear method self.liveView.delegate = nil;. This way you're sure to avoid any further message sent to the LiveViewController from the UIWebView.
You should read a bit more of documentation on Objective-C to better understand how it works.
Not sure if this is related but I noticed that you aren't setting yourself as the delegate anywhere in code which means that it must be connected in Interface Builder. Now when the view disappears, you are breaking that connection, but if the view were to re-appear and wasn't previously unloaded that connection will remain broken.
One of the most common reasons why an app may crash is to refer to or send a message to an object that has been already released from the memory. And this type of bug can be easily located using NSZombieEnabled and looking into the console message. So if you haven't already tried that, that's the first thing you must do.
The problem could be in LiveViewController but could be in the other view controllers as well. I wouldn't believe the problem is 100% in LiveViewController because the view controller wouldn't try releasing its view when the view is not shown unless it gets a memory warning. And you run the app using the simulator, it's unlikely it will have a memory warning unless you simulate one.
You would probably know that a view controller never create a view unless the view is used by an object. One of the other view controllers may have a silly bug in its view loading process which causes a crash. Or, you might have released another view controller by mistake. Make 100% sure that the other view controllers have no problem showing their views on their own, when you keep changing between their views (without showing LiveViewController).
So what I would do is to try NSZombieEnabled and check if it accesses a released object, and if it does, what the object is. Also, I will make a double check that the problem is related to LiveViewController. If it doesn't help I would log a message when LiveViewController and its liveView is deallocated (for liveView you need to subclass it). Because delegate property almost always does not retain an object, if the LiveViewController object is released (which shouldn't happen) and liveView still has a reference to it in the delegate property it will make a crash.
Crashes like this are almost always related to releasing an object that has already been released and deallocated.
Let XCode help you find the error. In XCode 4:
- In the toolbar, select the scheme list, and select 'Edit Scheme'
- Select the 'Run Your.app' in the list on the left.
- Under 'Environment Variables', add the following name/value pairs in the appropriate columns:
CFZombieLevel 3
NSZombieEnabled YES
Now when debug your app, you will get a message telling when -release is called on an object that already has a -retainCount of zero. Now you have a good clue to start your investigation.
Note that these flags prevent objects from being deallocated, so it is best to turn them on as needed to prevent out of memory errors.
Ok -- this one is weird. I have a singleton class that loads information from an XML file. I am using a delegate definition as follows (I define the delegate in a separate header file to make life easier):
#protocol ResourceClassDelegate <NSObject>
#optional
- (void)picturesDidStartLoading;
- (void)picturesDidFinishLoading;
#end
In the resource file, the delegate is defined correctly (I believe):
#property (assign) id<ResourceClassDelegate> delegate;
When using the delegate, the code in the resource class is as follows:
-(void)refreshPiecesOfHistoryWithOperation {
NSLog(#"Operation Started");
if ([delegate respondsToSelector:#selector(picturesDidStartLoading)])
[delegate picturesDidStartLoading];
self.picturePacks = [HistoryXMLParser loadPicturePacks];
[self.allPiecesOfHistory removeAllObjects];
// now lets put all of them in one big file...
for (PicturePack *pp in self.picturePacks) {
for (int ct = 0; ct < [[pp piecesOfHistory] count] ; ct++) {
[self.allPiecesOfHistory addObject:(PieceOfHistory *)[[pp piecesOfHistory] objectAtIndex:ct]];
}
}
NSLog(#"Operation Ended");
if ([delegate respondsToSelector:#selector(picturesDidFinishLoading)])
[delegate picturesDidFinishLoading];
}
Now... in the class that is listening to the delegate, it is assigned:
- (void)viewDidLoad {
[super viewDidLoad];
// now for the part that makes the loading all happen...
[[ResourceClass sharedResourceClass] setDelegate:self];
}
And in the listening class, the methods are defined....
#pragma mark ResourceClassDelegate
-(void)picturesDidStartLoading {
if (loadingActivity == nil)
loadingActivity = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
[self.view addSubview:loadingActivity];
[loadingActivity setCenter:[self.view center]];
[loadingActivity startAnimating];
}
-(void)picturesDidFinishLoading {
if (loadingActivity != nil) {
[loadingActivity stopAnimating];
[loadingActivity removeFromSuperview];
}
[self.tableView reloadData];
}
Now for the problem... every single time, in the listening class, the method (void)picturesDidFinishLoading is called. The method (void)picturesDidStartLoading never is called.
When I debug the code, in the resource class, the line
if ([delegate respondsToSelector:#selector(picturesDidStartLoading)])
[delegate picturesDidStartLoading];
never reaches the delegate method call - even if I remove the if statement. The line
if ([delegate respondsToSelector:#selector(picturesDidFinishLoading)])
[delegate picturesDidFinishLoading];
is always called.
any ideas?
Ok -- I figured it out....
The delegate was nil during the first call. The reason it is nil is because the function using the delegate was called in the source during the init method. The init method was not complete when the first test of the delegate was performed. At this time the delegate was nil because it is not instantiated until the the init method completes. The reason the second test of the delegate worked is because I submitted the process using an NSOperationQueue.
To fix the problem I have to move things around a bit... it's all about the timing!
Well now that was fun....
That's weird, try to remove #optional in the protocol declaration, and see if you get some warnings.
Try to print a log inside the method as well, other than that it looks fine.
My application has a view controller that extends UITableViewController. The initialization method looks like this:
- (id)initWithCoder:(NSCoder*)coder {
if (self = [super initWithCoder:coder]) {
self.tableView = [[UITableView alloc] initWithFrame:self.tableView.frame
style:UITableViewStyleGrouped];
}
return self;
}
When the view is initially loaded, it's displayed as UITableViewStyleGrouped. However, if my app ever receives a low memory warning, the above view changes to UITableViewStylePlain. There is no associated xib file with the View/Controller. The viewDidUnload and didReceiveMemoryWarning methods are straightforward:
- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}
- (void)viewDidUnload {
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
My question is, why does the table style change when I receive a memory warning?
It happens on the device and on the simulator. The device is a 3G iphone running OS 3.1.3, the simulator is running OS 3.1
In your initialization, you call [super initWithCoder:coder]. It would probably be better to override the designated initializer for UITableViewController, which is -initWithStyle:. What's probably happening is that when you create the table view controller by calling [super init…], it's being created with its tableView property already being set; that is, it's creating the table view on initialization. That's why your call to self.tableView.frame works—that shouldn't work if the value of self.tableView is nil. Here's a better implementation:
- (id)initWithCoder:(NSCoder*)coder {
if (self = [super initWithStyle:UITableViewStyleGrouped]) {
}
return self;
}