I'm trying to implament a callback mechanism where I pass in a block to the init of a class, and after some work that class calls me back. The block gets called and most everything works, except when I call anything on "self" within the block. I get Program received signal: “EXC_BAD_ACCESS” unless I comment out any reference to self within the block.
Am I wrong to think that I can access self within the block?
any advice would be greatly appreciated. This code is in a brand new "Universal app" and I'm currently working on the IPad portion, so running under the IPad simulator.
Some code:
__block LoginViewController *blockSelf = self;
LoginAlertView *alert = [[LoginAlertView alloc]
intWithPinPrompt:NO
title:#"Mobile Login"
myCallback:^(LoginAlertView *v){
DLog(#"self %#", blockSelf);
NSString *u = v.userNameText;
NSString *p = v.passwordText;
NSString *i = v.pinText;
[self authenticateUser:u
password:p
pin:i];
}];
and here is the some code from the LoginAlertView
- (id) intWithPinPrompt:(BOOL)pinPromptEnabled title:(NSString*)aTitle myCallback:(loginClicked)aCallback{
if (self = [self initWithTitle:aTitle
message:nil
delegate:self
cancelButtonTitle:#"Cancel"
otherButtonTitles:#"Login", nil]) {
hasPinPrompt = pinPromptEnabled;
theCallback = aCallback;
}
return self;
}
and the callback call
- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex{
if (theCallback) {
theCallback(self);
}
}
I changed to following line of code
theCallback = aCallback;
to
theCallback = [aCallback copy];
which is presenting me with the following error
Program received signal: “EXC_BAD_ACCESS”.
(gdb) bt
#0 0x029c8c97 in objc_msgSend ()
#1 0xbfffe560 in ?? ()
#2 0x00026f66 in -[LoginViewController show] (self=0x4a38450, _cmd=0x209c36c) at LoginViewController.m:18
#3 0x00026d3b in -[AuthenticatedViewController viewWillAppear:] (self=0x4c1fac0, _cmd=0x20b59ac, animated=0 '\0') at AuthenticatedViewController.m:17
one other thing, the definition of my block looks like this
typedef void(^loginClicked)(LoginAlertView*);
and the member variable is this
loginClicked theCallback;
also tried moving the declaration of the block up to a variable, and passing that in. this had the same results Anytime I use the "copy" on the bock I get the dreaded Program received signal: “EXC_BAD_ACCESS”. I thought maybe this was a IOS3.2 thing, so I tried running it under the IPhone 4.0 simulator, same results. Is there possibly a compiler setting that needs to be made in order to "Copy" the block onto the heap? I'm using LLVM1.5
First, what is blockSelf in your code?
Secondly, no, there is no reason why you can't use self and this is indicative of a bug in your code.
Specifically, you aren't copying the block. Blocks start out on the stack. Thus, when you say theCallback = aCallback;, you are storing a reference to an on-stack data structure. As soon as the defining stack frame goes away, that structure is no longer valid.
Change theCallback = aCallback; to theCallback = [aCallback copy]; (and add [theCallback release]; to your -dealloc method).
Related
I have a UIViewController. At the top of the UIViewController, I have declared
NSMutableArray *contacts;
In my viewDidLoad method, I call [self getContacts] which basically initializes my contacts array. It begins by initializing the array, and then it adds some objects:
if(contacts == nil)
contacts = [[NSMutableArray alloc] init];
[contacts removeAllObjects];
[contacts addObjectsFromArray:[some objects]];
So, now my contacts is initialized. In my viewDidLoad method, I even use contacts, and it works great. Later on, in a method, I need to retrieve the elements of contacts, however I am getting an EXC_BAD_ACCESS. Why is this? Why doesn't my contacts array keep the objects that I initialized it with in the beginning, and how do I fix this?
EDIT:
The error comes when I select a NavigationBarItem which then triggers a method buttonWasPressed. In that method, I simply have the following:
-(void)buttonWasPressed:(id)sender {
NSLog(#"button was pressed");
if(contacts == nil)
NSLog(#"contacts is nil!");
NSLog(#"contacts = %#",contacts);
}
And I see "button was pressed" printed, but then there is an EXEC_BAD_ACCESS.
That code all looks good, nothing wrong there. I would guess you are over-releasing elsewhere. Turn on Zombies - add NSZombieEnabled to YES in the executable arguments and it will break on the line so you can see what object is being over-released.
Im trying to create a simple callback using blocks.
I have a MainViewController which addSubView another DatePickerViewController.view i created a block like this
typedef void(^DateChangedBlock)(NSDate*);
And i have a method on my DatePickerViewController called
setOnDateChangedCallback:(DateChangedBlock)callback
I store the callback in a property of the DatePickerViewController. The DatePickerViewController's view is a UIDatePicker instance, ive bound an IBAction to the value changed to a method that does this.
- (IBAction)dateChanged:(id)sender {
if (dateChangedCallback != nil)
{
dateChangedCallback(nil);
}
}
Here is how i register the block in the MainViewController
DatePickerViewController *dateController = [[DatePickerViewController alloc] initWithNibName:#"DatePickerView" bundle:nil];
self.datePicker = dateController;
UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(0, 0, 100, 200)];
[self.view addSubview:textView];
DateChangedBlock myBlock = ^(NSDate *newDate) {
textView.text = #"testing";
};
[self.datePicker setOnDateChanged: myBlock];
[self.datePicker dateChanged:self]; // force trigger (this works).
When i force trigger the dateChanged method on the DatePickerViewController it works no problem. But when the datepicker itself triggers the method thru the IBAction i get a EXC_BAD_ACCESS error. The error occurs in this method on the "int retVal" line.
#import <UIKit/UIKit.h>
int main(int argc, char *argv[])
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
int retVal = UIApplicationMain(argc, argv, nil, nil); // THREAD 1: program received EXC_BAD_ACCCESS.**
[pool release];
return retVal;
}
What am i doing wrong?
You should copy your block when passing it to other method (such as attribute setter in your situation). So when setting the callback block do this:
[self.datePicker setOnDateChanged:[[myBlock copy] autorelease]];
You get the EXC_BAD_ACCESS cause block's variables used when creating the block don't get retained by the block itself. So when calling the block - variables do not exist anymore.
The accepted answer is wrong. You don't need to copy it in your MainViewController. Rather, the setOnDateChangedCallback: method which takes a block argument is responsible for copying it if it needs to store it in an instance variable (which I see it is doing, in the variable dateChangedCallback that is later used by another method). If dateChangedCallback is a synthesized property, you can accomplish this by declaring the property as copy instead of retain.
You can only update the UI from the UI thread. Since your block is running on another thread, you're getting the exception when updating the text of the textView. You can run code on the UI thread from within a block by using the main queue (dispatch_get_main_queue()).
Serious Problem here... i'm getting ECX_BAD_ACCESS if i try to NSLog an instance variable of my custom object. Following Function is called in my ViewController, payload holds String Data which is pulled from a url.
- (void) initVcardWithData:(NSString *)payload {
NSLog(#"1. initVcardWithData");
aVCard = [[vcardItem alloc] initWithPayload:payload];
VCardViewController *aVCardViewController = [[VCardViewController alloc] initWithVCard:aVCard];
[self presentModalViewController:aVCardViewController animated:YES];
[aVCard release];
}
So far so good. The initWithWithVCard function is as follows, theVCard and theVCardN are defined in #implementation and also set as a #property (nonatomic, retain) in (.h).:
-(id)initWithVCard:(vcardItem *)aVCard {
if(self = [super init]) {
theVCard = [aVCard retain];
theVCardN = [theVCard.PersonName retain];
}
NSLog(#"---- vCardViewController :: initWithVcard :: FirstName: %#", theVCard.PersonName.FirstName);
return self;
}
If i access the theVCardN object in my ViewController aVCardViewController within ViewDidLoad everything works like a charm. I set some labels with data from that object.
If i then try to access the instance variables from theVCardN within a function which is called from an IBAction which is connected to a button in View, i get an EXC_BAD_ACCESS error at the debugger console. The Function which tries to pull data from the instance variables is as follows:
-(IBAction)addressbookButtonTapped {
NSLog(#"RETAIN COUNT FOR theVCard: %i", [theVCard retainCount]);
NSLog(#"RETAIN COUNT FOR theVCardN: %i", [theVCardN retainCount]);
NSLog(#"Save to Adressbook: %#", theVCardN.FirstName);
//[self dismissModalViewControllerAnimated:YES];
}
The RetainCounter for theVCardN right before calling NSLog outputs "1". The NSLog Line then returns EXC_BAD_ACCESS in Debugger Console.
Any idea ?
Do not call -retainCount. Absolute retain counts are useless.
retainCount returns the absolute retain count of an object. The actual value will be an implementation detail that is very often completely out of your control as the system frameworks may do any number of things internally to cause the retain count to be modified in ways you don't expect.
It is useless for debugging and their are a wealth of tools that are specifically focused on tracking down these kinds of issues.
First, if there is a crash, there is a backtrace. Post it. Probably not that interesting in this case, but, still, always look to the backtrace to at least confirm that it is crashing where/how you think it is.
From the evidence posted, it sounds like theVCardN.FirstName is either set to garbage or the underlying string has been over-released. Turn on zombie detection mode and see if that is the case. Since it is crashing on FirstName, then show the code related to creating/storing the FirstName.
Also, instance variables and methods should always start with a lowercase letter; PersonName should be personName & FirstName should be firstName.
Maybe i'm reading the code wrong or misunderstanding your class structure, but it looks like you logging:
NSLog(#"Save to Adressbook: %#", theVCardN.FirstName);
Above, where you say it is still working, you are logging:
theVCard.PersonName.FirstName
Are you missing the "PersonName"? Meaning you should be logging:
NSLog(#"Save to Adressbook: %#", theVCardN.PersonName.FirstName);
For reference, I've already read:
memory management question -- releasing an object which has to be returned
iPhone: Return NSMutableArray in method while still releasing
Releasing objects returned by method
Which I thought would help :).
This app is a teaching tool and is intended to help people visualize simple genetics. Just some background so the variable names and stuff will make sense. Here's the main code that executes when the app runs:
- (void)viewDidAppear:(BOOL)animated {
ThingzCore *core = [[ThingzCore alloc] init];
ThingzThing *thing1 = [[ThingzThing alloc] init];
thing1.breed = #"AB";
thing1.pattern = #"AC";
thing1.color = #"CA";
thing1.gender = #"XY";
thing1.generation = 1;
thing1.isEgg = NO;
ThingzThing *thing2 = [[ThingzThing alloc] init];
thing2.breed = #"CD";
thing2.pattern = #"BA";
thing2.color = #"CB";
thing2.gender = #"XX";
thing2.generation = 1;
thing2.isEgg = NO;
NSLog(#"Breeding GD BR PT CL G");
ThingzThing *child = [core mateFather:thing1 withMother:thing2];
NSLog(#"Round 1: %# %# %# %# %d",child.gender,child.breed,child.pattern,child.color,child.generation);
sleep(10);
child = [core mateFather:thing1 withMother:thing2];
NSLog(#"Round 2: %# %# %# %# %d",child.gender,child.breed,child.pattern,child.color,child.generation);
sleep(10);
child = [core mateFather:thing1 withMother:thing2];
NSLog(#"Round 3: %# %# %# %# %d",child.gender,child.breed,child.pattern,child.color,child.generation);
sleep(10);
child = [core mateFather:thing1 withMother:thing2];
NSLog(#"Round 4: %# %# %# %# %d",child.gender,child.breed,child.pattern,child.color,child.generation);
sleep(10);
[thing1 release];
[thing2 release];
[core release];
}
And here's what happens when I run it in various ways:
Running without breakpoints, it crashes, with no console message, after the 2nd sleep() but before the "Round 3" NSLog.
Running with breakpoints enabled, but none defined, it runs through the entire sequence. After the fourth sleep(), it crashes with EXC_BAD_ACCESS.
Running with breakpoints enabled and NSZombiesEnabled, it does the same thing as above - no further information, just EXC_BAD_ACCESS.
Running in Instruments, no leaks are shown.
This is the routine being called four times:
-(ThingzThing *)mateFather:(ThingzThing *)father
withMother:(ThingzThing *)mother {
// will we be doing a mutation?
int mutationPercentage = father.generation + mother.generation;
int mutationNumber = (arc4random() % ((unsigned)100 + 1));
BOOL isMutation = NO;
if (mutationNumber <= mutationPercentage) {
isMutation = YES;
}
// get possibilities
NSArray *possibilities = [self possibilitiesByMatingFather:father
withMother:mother
mutations:isMutation];
// randomly select one of the possibilities
int keeping = (arc4random() % ((unsigned)[possibilities count]));
return [possibilities objectAtIndex:keeping];
}
Without pasting in the ENTIRE code, the possibilitiesByMatingFather:withMother:mutations function is returning an NSMutableArray. That routine declares the array by using:
NSMutableArray *possibilities = [NSMutableArray array];
It then:
return possibilities;
It does not send a release or autorelease message to possibilities; my understanding is that creating the array the way I have is an implicit autorelease. I didn't want to alloc the array, because I'm returning it, so wouldn't have the opportunity to explicitly release it.
The objects held in the possibilities NSMutableArray are of a custom class. They are added as follows:
ThingzThing *newThing = [[ThingzThing alloc] init];
newThing.breed = choiceBreed;
newThing.gender = choiceGender;
newThing.color = choiceColor;
newThing.pattern = choicePattern;
newThing.generation = mother.generation + father.generation;
newThing.name = #"";
newThing.isEgg = YES;
[possibilities addObject:newThing];
[newThing release];
Which seems to work most of the time. At least, when breakpoints are enabled, the program runs through the code without complaint until the end, as noted above.
Any suggestions on what I'm doing wrong, here? It's obviously memory management issues of some kind, but I can't sort it in my head.
BTW, in a vain, throwing-things-at-the-wall attempt to figure it out, I did modify the one line from the main routine as follows:
// get possibilities
NSArray *possibilities = [[self possibilitiesByMatingFather:father
withMother:mother
mutations:isMutation] retain];
To no avail. Same results. So the problem isn't in retaining the array returned by possibilitiesByMatingFather:withMother:mutations. Forcing a retain on that return isn't helping.
Frequently in this type of situation, the actual error is not at the location shown in the debugger when the app halts.
For example, the debugger may be pointing to a method call, but the problem actually occurs inside the method -- not when the method is called.
To track things down, I would suggest setting a breakpoint just before the method call that triggers the error -- in your case, this would be the mateFather: withMother: call. Then step into that method. There is a good chance you will find that the problem happens inside that method -- or even inside a method called from within that method.
Check you have the correct property declarations of the string properties of class ThingzThing.
e.g.
#property (nonatomic, retain) NSString* breed;
NEED to be retain or copy NOT assign...
Found it. Buried eight method calls down, I was sending release to an NSArray that was obviously autoreleasing. When the initial calling routine (viewDidAppear) fell down into autorelease mode, it tried to autorelease the already-released object, and exploded. Good grief - is there any way XCode could have helped me track that down?
In any event, in case anyone runs across this, make bloody sure you're not sending a release message to something that you didn't explicitly alloc yourself. If you didn't alloc it, odds are it was autoreleasing itself, and you sending a release to it takes the retain count negative, and the Foundation framework vomits with an EXC_BAD_ACCESS.
I am writing an iPhone app that that is trying to create a second a view when the user clicks on an element in UITableView. The code looks like
ReplyToViewController *reply = [[ReplyToViewController alloc] initWithNibName:#"ReplyTo" bundle:nil];
reply.delegate = self;
Message *message = [resultData objectAtIndex:indexPath.row];
int dbid = [message.bizid intValue];
NSLog(#"dbid=%d",dbid);
reply.currentMessage = message;
reply.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
[self presentModalViewController:reply animated:YES];
The reply object gets created properly and the view is proper. Last line in above code segment calls some framework code which eventually calls the viewDidLoad method of the ReplyToViewController. Address of the reply object in the above code and the address of the object in viewDidLoad is not same.
Any idea where this new object is coming from? How do I debug? I also added init method the following method in ReplyToViewController hoping that it will get called and I can find who is creating this new object. But it does not stop in this method.
Any help will be greatly appreciated.
- (id) init
{
/* first initialize the base class */
self = [super init];
return self;
}
// Following gets called from the 1st code segment.
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil])
{
// Custom initialization
}
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
NSLog(currentMessage.text]; // THIS returns nil and the program fails later in the code.
}
I'm sure this is unrelated, but I figure this:
NSLog(currentMessage.text];
Should be this:
NSLog(currentMessage.text);
Also, I've found that Analyzing (Cmd+Shift+A) my code always helps to track down potential memory leaks and prevent overzealous memory allocation.
The most likely explanation is a reporting error.
Usually when people see a different address for an object it's because they used the wrong format descriptor in their log statements.
A common error is:
NSLog(#"Object address=%i", myObject); // any numerical formatter %d,%f...
... which produces a random number. You really want:
NSLog(#"Object address=%%qX",&myObject);
... which dumps the address in hex.
Another mistake is:
NSLog(#"Object address=%%qX",&[myObject description]);
... which returns the address of the description string which changes every time.
There are others but you get the idea.
If you're using log statements, check the address in the debugger instead to confirm it's a different object.
Unrelated, but I would get rid of the class' initializer methods because they don't do anything but call the super. You might as well just let the compiler default to the super if you don't customize.