i m parsing a json in table view.clicking the tableview navigates to nextview.after few clicks the app gets crashed.I have set NSZombieEnabled in my environmental variable and i got this message in my console*** -[NSCFString isEqual:]: message sent to deallocated instance 0x1f31d0
how to trace back which variable exactly i m getting the leak would be great if you guys could help me out.
Did you try enabling the exception breakpoint? You can try tracking that zombie on instruments, the long way:
Run your app on Intruments.
In instruments, select Object allocations tool(automatically selected if you select leaks tool).
Click on the little "i" on top left, within the Allocations tool.
Select "Enable NSZombie detection".
Press the record button and let your app run.
Go through the execution of the app untill it crashes. As soon as there is a crash, you'd see a pop up saying that there was a EXC_BAD_ACCESS. Click on the little -> on the pop up to see the object that has turned into a zombie and the line of code responsible.
Related
I am following the Stanford University iOS development course on iTunes U.
In one of the demos (that I have been trying to follow), there is this code that loads the property list from an NSURL and returns it as NSMutableDictionary.
-(NSMutableDictionary *) words
{
NSURL *wordsURL=[NSURL URLWithString:#"http://cs193p.stanford.edu/vocabwords.txt"];
words=[[NSMutableDictionary dictionaryWithContentsOfURL:wordsURL] retain];
return words;
}
The application is successfully built, but at runtime it gives the following error and gets stuck:
I can't figure out what the problem is. Can you please help?
You're stopped at a breakpoint. That's a debugging tool, not an error. See the blue arrow/tab in the left margin, where the line numbers are? Drag that away and drop it anywhere (you'll see a "poof") to remove it, then run your project again.
You can also deactivate all breakpoints by typing ⌘-Y, the key equivalent for the menu item Debug>Deactivate Breakpoints, or you can view all your breakpoints in the Breakpoint Navigator (hit ⌘-6).
When execution stops like this, you can continue from the breakpoint, either by typing continue at the debugger prompt in the Console:
(lldb) continue
Or hitting the "Play" button in the debugger controls. You can also type Control-⌘-Y, which is the equivalent for the menu item Debug>Continue.
This isn't an error. You just set a breakpoint (probably without knowing it).
Drag the little blue Chevron in the column at the left out of the way. You will see it disappear and go poof, and then you can rebuild your app and you should see it run properly.
Now, that said, I think there are some memory management mistakes in your code, but we can return to those later. ;-)
The program is stopping because you have a breakpoint.. That's the blue arrow on the left of the code. Right-click it and delete.
I am following the Stanford University iOS development course on iTunes U.
In one of the demos (that I have been trying to follow), there is this code that loads the property list from an NSURL and returns it as NSMutableDictionary.
-(NSMutableDictionary *) words
{
NSURL *wordsURL=[NSURL URLWithString:#"http://cs193p.stanford.edu/vocabwords.txt"];
words=[[NSMutableDictionary dictionaryWithContentsOfURL:wordsURL] retain];
return words;
}
The application is successfully built, but at runtime it gives the following error and gets stuck:
I can't figure out what the problem is. Can you please help?
You're stopped at a breakpoint. That's a debugging tool, not an error. See the blue arrow/tab in the left margin, where the line numbers are? Drag that away and drop it anywhere (you'll see a "poof") to remove it, then run your project again.
You can also deactivate all breakpoints by typing ⌘-Y, the key equivalent for the menu item Debug>Deactivate Breakpoints, or you can view all your breakpoints in the Breakpoint Navigator (hit ⌘-6).
When execution stops like this, you can continue from the breakpoint, either by typing continue at the debugger prompt in the Console:
(lldb) continue
Or hitting the "Play" button in the debugger controls. You can also type Control-⌘-Y, which is the equivalent for the menu item Debug>Continue.
This isn't an error. You just set a breakpoint (probably without knowing it).
Drag the little blue Chevron in the column at the left out of the way. You will see it disappear and go poof, and then you can rebuild your app and you should see it run properly.
Now, that said, I think there are some memory management mistakes in your code, but we can return to those later. ;-)
The program is stopping because you have a breakpoint.. That's the blue arrow on the left of the code. Right-click it and delete.
I'm new to NSZombie but I have a problem with my app crashing with EXC_BAD_ACCESS. I'm having real trouble finding the object that is causing the problem. Looking online I followed instructions to enable zombie objects.
The problem I'm having has been reported by another person on that page. Enabling zombie objects stops the bad access error but gives me no information. Nothing is printed by NSLog. Is there somewhere else I should look, or am I doing something wrong? I don't really know my way round XCode or a Mac very well as I'm mainly a C# programmer.
Any help would be most welcome.
1) Run your app on Intruments.
2) In instruments, select Object allocations tool(automatically selected if you select leaks tool).
3)Click on the little "i" on top left, within the Allocations tool.
4) Select "Enable NSZombie detection".
5) Press the record button and let your app run.
6) Go through the execution of the app untill it crashes. As soon as there is a crash, you'd see a pop up saying that there was a EXC_BAD_ACCESS. Click on the little -> on the pop up to see the object that has turned into a zombie and the line of code responsible.
Sorry I am unable to upload a screenshot, as am at work.
Expand your project Executable and right click on it. and click on GetInfo->Argument tag aat end of the window you see plus and minus sign button click on + sighn button and write
Name Value
NSZombieEnabled YES
then after execute your project and whenever crash your application click on run munu-> console you see there why your application crash. please try this may be this will help you.
I'm getting an EXC_BAD_ACCESS crash at startup and Xcode says the crash is at the NSApplicationMain line in my main.m file. The crash happens 99% of the time and when I run it with zombies enabled the crash never happens. Has anyone seen this before? How can I possibly debug this?
If you are running Xcode4 there default is to show very little of the call stack, move the slider at the bottom to the right. You may well not find any of your code but you should be able to get a good idea of what was going on. If it was a notification or selector after delay you will see that the Runloop dispatch and that will also give you a clue.
Finally, go old school, the way we did it in the day of coding forums, punch cards and only a couple of compiles a day: study your code. Know what every line of code does and why it is there.
As #Danra said, do run the Xcode Analyzer and fix all complaints.
The reason why running with zombies enabled resolves the bad access is probably that a) In this mode objects don't really get deallocated when their retain count reaches zero, and b) That your original crash is due to accessing an already deallocated object.
However with zombies enabled, instead of the crash I think you should see in the debug console the access to the deallocated object.
I also recommend using the static analyzer ("Analyze" in the XCode menus) in hope that it finds the culprit.
I am relatively new to Xcode4 and I would like to know how can I identify a double release with it.
In the debugger I see a line like *** -[NSConcreteMutableData release]: message sent to deallocated instance 0x60b63fe0.
The problem is that knowing the address doesn't help a lot identifying the object and also the object type doesn't help too much identifying it.
I read http://www.friday.com/bbum/2010/01/10/using-malloc-to-debug-memory-misuse-in-cocoa/ but I did not found this to be too successful.
You can enable the NSZombieEnabled environment variable - see How do I set up NSZombieEnabled in Xcode 4? for instructions on how to do this on Xcode 4.
What this means is that released objects are kept around in memory, so the debugger can still find out the type of objects. When the crash occurs, you are told of the object in question.
The "Zombies" Instruments tool is great for detecting bugs of this type - it actually enables NZZombieEnabled and you can use it to find out exactly which line of code the crash occurs.
You can replace the release method using categories for testing purposes, this is not designed to work like that as part of the language but in the past I have found success it trying to do some testing, usually all you find out is that an autorelease pool is releasing you object.
You are sending a release message to something which already is released or having retainCount 0. Hence, its giving such an error message. Actually, my answer over here might help.
Use the profiler for Zombies to track down the actual object. It will automatically enable NSZombies and more importantly keep a history of all release and autorelease messages.
Use Profile menu command under Product.
In the profiling template selection dialog that appears, select Zombies.
Click the Record button in the toolbar (Command-R) to begin recording. Use your app normally. If a call is made to a deallocated object, a flag is inserted in the timeline pane and a Zombie Messaged dialog appears.
Click the focus arrow next to the zombie’s memory address to display the memory history of the zombie object in the detail pane, along with corresponding reference counts and method calls.
Here is the apple documentation with pictures:
https://developer.apple.com/library/content/documentation/DeveloperTools/Conceptual/InstrumentsUserGuide/EradicatingZombies.html
Try using the property retainCount. If an object has a retainCount == 0 then it will be freed. Ultimately you will not be able to send it a release message.