automatic-ref-counting

问题 If i understood correctly we could classify void * as a "C retainable pointer type". So, assigning it to an Objective-C object will be implicitly bridged. However, compiler raises error that explicit bridging is required. const void * somePtr = (void *)0x12345678; - (void)someMethod:(id)sender { NSObject *obj = (NSObject *)somePtr; } Also, i checked the null pointer constant and it compiles without explicit bridging. NSObject *obj = (void *)0; I am using XCode 4.5(Clang 4.1 (tags/ Apple/clang

问题 We have some code today that takes an NSArray and passes it as a argument list to -[NSString initWithFormat:arguments] and we're trying to get this to work with ARC. Here's the code were using NSString* format = @"Item %s and Item %s"; // Retrieved elsewhere NSArray* args = [NSArray arrayWithObjects:@"1", @"2", nil]; // Retrieved elsewhere // http://cocoawithlove.com/2009/05/variable-argument-lists-in-cocoa.html char* argsList = (char*) malloc(sizeof(NSString*) * args.count); [args getObjects

问题 This question already has an answer here : Closed 7 years ago . Possible Duplicate: using ARC, lifetime qualifier assign and unsafe_unretained What's the difference between the two? @property(unsafe_unretained) MyClass *delegate; @property(assign) MyClass *delegate; Both are non-zeroing weak references, right? So is there any reason why I should write the longer and harder to read unsafe_unretained instead of assign ? Note: I know there is weak which is a zeroing reference. But it's only iOS

问题 I have a property that I do not synthesize, instead I create a getter and setter myself. Therefore, the ARC keywords (strong or weak) have no meaning, I assume, so I eliminate them. This works fine on Xcode 4.3, but when my coworker opens them on XCode 4.2 the compiler complains that there is no strong/weak keyword, so I instructed him to meaninglessly enter the keyword back in again. Which is correct (with or without keywords)? To be clear: I have a property like this @property (nonatomic)

问题 I have done abit of research on stackoverflow and apple's documentation about ARC and Weak/Unowned self (Shall we always use [unowned self] inside closure in Swift). I get the basic idea about strong reference cycle and how it is not good as they cause memory leaks. However, I am trying to get my head around when to use Weak/Unowned self in closures. Rather then going into the "theory", I think it would really really help if someone could kindly explain them in terms of the bottom three cases

问题 I have a ARC (automatic-reference-counting) app that builds a static library (also ARC). The app will launch fine but when the an action is performed that reads or writes to a @property in the static library the app will crash with this error: dyld: lazy symbol binding failed: Symbol not found: _objc_setProperty_nonatomic Referenced from: /var/mobile/Applications/0E7ADBB4-FFE5-4CEB-B418-8A35A92E99D4/MyApp.app/MyApp Expected in: /usr/lib/libobjc.A.dylib dyld: Symbol not found: _objc

问题 Prior to ARC, if I wanted a property to be readonly to using it but have it writeable within the class, I could do: // Public declaration @interface SomeClass : NSObject @property (nonatomic, retain, readonly) NSString *myProperty; @end // private interface declaration @interface SomeClass() - (void)setMyProperty:(NSString *)newValue; @end @implementation SomeClass - (void)setMyProperty:(NSString *)newValue { if (myProperty != newValue) { [myProperty release]; myProperty = [newValue retain];

问题 Before ARC I had the following code that retains the delegate while an async operation is in progress: - (void)startAsyncWork { [_delegate retain]; // calls executeAsyncWork asynchronously } - (void)executeAsyncWork { // when finished, calls stopAsyncWork } - (void)stopAsyncWork { [_delegate release]; } What is the equivalent to this pattern with ARC? 回答1: Why not just assign your delegate object to a strong ivar for the duration of the asynchronous task? Or have a local variable in

问题 I've asked this question asking about the guarantees of the lifetime of a reference in a local variable and was referred to this thread in which the exact semantics of the lifetime of references to class instances were discussed. AFAICT from that thread, a class instance may be de-initialized right after the last usage of a variable containing the last reference, even before other expressions in the same statement are evaluated. It is argued there that allowing this behavior is necessary to

问题 I am new to iphone development. I have learnt that ARC is a new feature introduced in IOS now . My question is, I have an old Non ARC project with the release written manually, is it possible to switch this project from non ARC to ARC ? Thanks, Raj 回答1: Make sure you are using version control, then use: Edit > Refactor > Convert to Objective-C ARC… 来源： https://stackoverflow.com/questions/12171922/switching-the-non-arc-project-into-arc