If I try to run this, I get the error:
"Initializer element is not a compile-time constant."
Can anybody explain to a newly like me why this is happening?
your code is correct. I think you have written it outside any function.
what I meant is the line of code ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init]; must be in any method and NOT global(outside function so that the library variable becomes global)
Related
Im wondering if calling [[MyClass alloc] init] on an already existing (allocated) object create a leak in ARC? or does it manage the release and reallocation for you?
would doing the following be more proper:
myObject = nil;
myObject = [[MyClass alloc] init];
which is more appropriate? is there another way to do this properly?
With ARC, you don't need to set the myObject to be nil before reallocating it,only this line of code will be fine:
myObject = [[MyClass alloc] init];
When xcode compiles the code, it will automatically add the right release mechanism in.
I do apologize if this have been asked before but i have not found a good answer.
When i run the Instruments i get a leak on this line in the code, not in main:
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
I have been looking around and read somewhere that it may be a bug. Could someone please help me and share some light on this?
I did notice that i have the same name, "pool", in main also.
The name doesn't matter; there may be hundreds of variables named pool throughout the codebase. What matters is scope.
Typically, you'll see this:
- someMethod
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
... do stuff ...
id something = [anObject retain];
[pool drain];
return [something autorelease];
}
I.e. is your pool being drained?
(drain exists on iOS; see the documentation. However, in all cases, it is better to use #autoreleasepool{ ... }; it works in ARC and MRR.)
I had this problem as well, my first problem on the first day learning how to code!
All I did was remove outright the entire line starting with:
NSAutoreleasepool *pool = [[NSAutoreleasepool alloc] init];
replace it with:
#autoreleasepool {
Then I deleted at the bottom of my program:
[pool release];
Then closed off with the squiggly brackets.
I don't know why it works, my first day remember but it runs my program from the example book fine.
I'm running some code in a background thread to get a text file from a service. That code fires a delegate at some point. It throws as SIGABRT error once the delegate is being called and well, my concept doesn't sound convincing to me either.
The code running at the background thread:
- (void)FetchStores
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// Fetch from service
NSString *serviceURL = #"http://../index.html";
NSURL *myURL = [NSURL URLWithString:serviceURL];
NSData *dataRep = [NSData dataWithContentsOfURL:myURL];
storesList = [[Stores alloc] init];
storesList.storesDelegate = self;
[storesList FetchWithNSData:dataRep];
[pool release];
}
The storesList object will fire a delegate once all the stores have been extracted from the service. The delegate is getting caught by a function at the main thread.
Do you have any suggestions what am I doing wrong ?
Thank you,
f.
When calling the delegate, somewhere, you should make the switch to the main thread.
Especially if somewhere, you are updating the UI based on the data fetched.
You can use
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait
to make the switch.
Maybe like this:
storesList = [[Stores alloc] init];
storesList.storesDelegate = self;
[storesList performSelectorOnMainThread:#selector(FetchWithNSData:) withObject:dataRep waitUntilDone:TRUE];
In your case, you should use waitUntilDone:TRUE so that the FetchWithNSData method gets a chance to retain the data.
It seems quite likely that FetchWithNSData: does not retain the passed dataRep and the data gets deallocated on the next line where you drain the local autorelease pool?
Ok, here goes.
Being a Java developer I'm still struggling with the memory management in ObjectiveC. I have all the basics covered, but once in a while I encounter a challenge.
What I want to do is something which in Java would look like this:
MyObject myObject = new MyObject(new MyParameterObject());
The constructor of MyObject class takes a parameter of type MyParameterObject which I initiate on-the-fly.
In ObjectiveC I tried to do this using following code:
MyObject *myObject = [[MyObject alloc] init:[[MyParameterObject alloc] init]];
However, running the Build and Analyze tool this gives me a "Potential leak of an object" warning for the MyParameter object which indeed occurs when I test it using Instruments. I do understand why this happens since I am taking ownership of the object with the alloc method and not relinquishing it, I just don't know the correct way of doing it.
I tried using
MyObject *myObject = [[MyObject alloc] init:[[[MyParameterObject alloc] init] autorelease]];
but then the Analyze tool told me that "Object sent -autorelease too many times".
I could solve the issue by modifying the init method of MyParameterObject to say return [self autorelease]; in stead of just return self;. Analyze still warnes about a potential leak, but it doesn't actually occur. However I believe that this approach violates the convention for managing memory in ObjectiveC and I really want to do it the right way.
Thanx in advance.
Ok, here's a suggestion.
MyParameter *param = [[MyParam alloc] init];
MyObject *obj = [[MyObject alloc] initWithParam:param]; // do you know if param is retain'd or not?
[param release];
Why do it this way? This is the pattern used throughout ObjC/Cocoa. You add objects to NSArrays this way:
MyThing *thing = [[MyThing alloc] init];
[myMutableArray addObject: thing]; // this calls [thing retain]
[thing release];
You may also want to try to do this:
MyObject *obj = [[MyObject alloc] initWithParam: [MyParameter parameter]];
where:
+ (id) parameter
{
return [[[self alloc] init] autorelease];
}
that way you don't have to worry about it. This is the same as
[NSData data];
[NSArray array];
I hope that helps. Generally, it isn't a good idea to use init during another method call (like a setter or another init). Hiding it behind a Class Method (+ (id) parameter) means the user knows it'll be autorelease'd.
If you're ever unclear about how many retain's or release's something has, you can always do something like this:
[EDIT]
Caveat: Apparently you should never use -retainCount. I find it useful for teaching learners the basics of retain'd Memory Management, but the point is well taken.
Never Use it in actual code or for performance testing. This is only used to learn what retain does (and I believe it functions properly in this case). It will never give you an intelligent answer for an object which is autorelease'd or further retain'd by a NSArray or Other Foundation/AppKit/UIKit Classes
MyParameter *param = [[MyParam alloc] init];
NSLog(#"param retain count: %d",[param retainCount]); // should be 1
MyObject *obj = [[MyObject alloc] initWithParam:param];
NSLog(#"param retain count: %d",[param retainCount]); // should be 2, if MyObject retains it.
[param release];
NSLog(#"param retain count: %d",[param retainCount]); // should be 1
Also, when you dealloc MyObject, you'll need to release param if you retain'd it during initialization.
The following guide put out by Apple should help you to understand Objective-C Memory Management a little better.
MyThing *thing = [[MyThing alloc] init];
[otherThing methodWithAThing:thing];
[thing release];
or:
[otherThing methodWithAThing:[[[MyThing alloc] init] autorelease]];
or (if there is a "convenience constructor" on the class you're using):
[otherThing methodWithAThing:[MyThing thing]];
MyObject *myObject = [[MyObject alloc] init:[[[MyParameterObject alloc] init] autorelease]];
should be ok, if there is no release in the init (there should definitely not be a release in the init). I often make a class method which makes a autoreleased object. So the code would be:
// using it:
MyObject *myObject = [[MyObject alloc] init:[MyParameterObject defaultParameters];
// in the class implementation of MyParameterObject
+ (MyParameterObject*) defaultParameters{
MyParameterObject* out = [[MyParameterObject alloc] init];
// set some values
return [out autorelease];
}
[[MyObject alloc] init:[[[MyParameterObject alloc] init] autorelease]]
Without knowing what's going on in the init method, this seems fine.
NB, though, that it's more Objective-Cish to spell this "initWithParameterObject:". Though they gag people new to the language, Obj-C's descriptive method names are actually really helpful for code readability.
There have been a few threads on this topic but none have been able to solve my problem. Essentially I am trying to add a custom object to an NSMutableArray and it doesn't seem to be adding. I don't get any errors but I get a warning saying that my array is an "unused variable" so it looks like it is not getting used. See code below. Any help is appreciated!
Here is the initialization in the app delegate (on run time it says this array is not being used):
NSMutableArray *organArray = [[NSMutableArray alloc] init];
Here is my object class organ.m (I am importing the app delegate, the rootviewcontroller and the organ.h file)
Organ *organObj = [[Organ alloc] initWithPrimaryKey:primaryKey];
organObj.organName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(selectstmt,1)];
organObj.isDirty = NO;
[appDelegate.organArray addObject: organObj];
[organObj release];
I know the organObj.organName is getting the correct values from my sqlite db because I can output them to the console. They just don't seem to be getting added to the array and the fact that it says the array is not being used means something is wrong.
Thanks in advance
Just a guess but if organArray is intended to be a member of your app delegate, you are creating a new organArray when prefixing it with "NSMutableArray" so if I understand your code, change your app delegate to:
organArray = [[NSMutableArray alloc] init];
instead of:
NSMutableArray *organArray = [[NSMutableArray alloc] init];