Open your project and select Edit -&gt; Refactor -&gt; Convert to Objective-C ARC.
 This will start checking your code if it is ready for the conversion.

See also Clang documentation: [Objective-C Automatic Reference Counting (ARC)][1]

How to disable ARC has been answered [here][2]

  [1]: https://clang.llvm.org/docs/AutomaticReferenceCounting.html
  [2]: https://stackoverflow.com/questions/7837024/how-to-disable-xcode4-2-automatic-reference-counting

Following are the steps which I did and it worked for me

1. Select `Project`
2. Select `Targets`
3. From the right panel, select `Build Settings`
4. Search for &quot;Automatic Reference Counting&quot;;
5. Locate `Apple LLVM compiler 3.0 - Language` and `Objective-C Automatic Reference Counting` and select `NO` in all three sections.

![enter image description here][1]


  [1]: http://i.stack.imgur.com/UATIJ.png

When you migrate a project to use ARC, the -fobjc-arc compiler flag is set as the default for all Objective-C source files. You can disable ARC for a specific class using the -fno-objc-arc compiler flag for that class. In Xcode, in the target Build Phases tab, open the Compile Sources group to reveal the source file list. Double-click the file for which you want to set the flag, enter -fno-objc-arc in the pop-up panel, then click Done.

In Xcode 5.0.2, select your project in Navigatior, select Build Settings, search for Apple LLVM 5.0 - Language - Objective C and change Objective-C Automatic Refence Counting to NO


I have to list all &quot;**shift**&quot; data to be assigned to an &quot;**employee**&quot; but shift data must not be included if it is already existing in employee&#39;s data. Let&#39;s see the image sample.  

![No filtering yet][1]


This query solves the problem. I found this here:  
[Scott&#39;s Blog][2]  

    select * from shift where not exists 
    (select 1 from employeeshift where shift.shiftid = employeeshift.shiftid
    and employeeshift.empid = 57);  

Let&#39;s see the result:  

![Filtered][3]  

Now my question is, how could I make this in linQ ? I&#39;m using entity framework.  
Hope someone could help. Thanks a lot!!!


  [1]: http://i.stack.imgur.com/T2Sco.png
  [2]: http://miniburb.wordpress.com/2007/05/31/sql-outer-join-vs-where-not-in-vs-not-exists/
  [3]: http://i.stack.imgur.com/STsh2.png

How to SELECT WHERE NOT EXIST using LINQ?

Is there a way to get the current view controller from the AppDelegate? I know there is rootViewController, but that&#39;s not what I&#39;m looking for.

Current view controller from AppDelegate?

If a project has already been created with ARC disabled, how do I enable it and vice versa?

How to enable/disable ARC in an xcode project?

<p>If a project has already been created with ARC disabled, how do I enable it and vice versa?</p>


I&#39;m developing an iPhone app. In a label, I want to show an user&#39;s first letter of the name uppercase. How do I do that?

How to make first letter uppercase in a UILabel?

I try to change font color from white to black for `UISegmentedControl` (for iOS 4.*)

    UISegmentedControl *button = [[[UISegmentedControl alloc] initWithItems:[NSArray arrayWithObjects:itemTitle, nil]] autorelease];
    button.momentary = YES;
    button.segmentedControlStyle = UISegmentedControlStyleBar;
    button.tintColor = [UIColor redColor];      
    for (id segment in [button subviews]) {
        for (id label in [segment subviews]) {
            if ([label isKindOfClass:[UILabel class]]) {
                UILabel *titleLabel = (UILabel *) label;
                [titleLabel setTextColor:[UIColor blackColor]];
            }
        }
    }
    UIBarButtonItem *barButtonItem = [[[UIBarButtonItem alloc] initWithCustomView:button] autorelease];

But text color does not changed. What I should do for change text color for `UISegmentedControl`?




How to change font color of UISegmentedControl

What is the most efficient way to obtain an NSDate object that represents midnight of the current day?

How can I get an NSDate object for today at midnight?

I&#39;m trying to wrap my head around some of the differences in usage and syntax in C vs. Objective-C.  In particular, I want to know how (and why) the usage differs for the dot operator and the arrow operator in C vs. Objective-C.  Here is a simple example.

**C Code:**

    // declare a pointer to a Fraction
    struct Fraction *frac;

    ...

    // reference an &#39;instance&#39; variable
    int n = (*frac).numerator;     // these two expressions
    int n = frac-&gt;numerator;       // are equivalent


**Objective-C Code:**

    // declare a pointer to a Fraction
    Fraction *frac = [[Fraction alloc] init];

    ...

    // reference an instance variable
    int n = frac.numerator;        // why isn&#39;t this (*frac).numerator or frac-&gt;numerator??

So, seeing how `frac` is the same in both programs (i.e. it is a pointer to a Fraction object or struct), why are they using different syntax when accessing properties?  In particular, in C, the `numerator` property is accessed with `frac-&gt;numerator`, but with Objective-C, it is accessed using the dot operator, with `frac.numerator`.  Since `frac` is a pointer in both programs, why are these expressions different?  Can anyone help clarify this for me?

Dot (&quot;.&quot;) operator and arrow (&quot;-&gt;&quot;) operator use in C vs. Objective-C

I usually see this question asked the other way, such as https://stackoverflow.com/questions/5031230/ios-must-every-ivar-really-be-property (and I like bbum&#39;s answer to this Q).

I use properties almost exclusively in my code.  Every so often, however, I work with a contractor who has been developing on iOS for a long time and is a traditional game programmer.  He writes code that declares almost no properties whatsoever and leans on ivars.  I assume he does this because 1.) he&#39;s used to it since properties didn&#39;t always exist until Objective C 2.0 (Oct &#39;07) and 2.) for the minimal performance gain of not going through a getter / setter.

While he writes code that doesn&#39;t leak, I&#39;d still prefer him to use properties over ivars.  We talked about it and he more or less sees not reason to use properties since we weren&#39;t using KVO and he&#39;s experienced with taking care of the memory issues.

**My question is more...  Why would you ever want to use an ivar period - experienced or not.  Is there really that great of a performance difference that using an ivar would be justified?**

Also as a point of clarification, I override setters and getters as needed and use the ivar that correlates with that property inside of the getter / setter.  However, outside of a getter / setter or init, I always use the `self.myProperty` syntax.


----------

Edit 1
------

I appreciate all of the good responses.  One that I&#39;d like to address that seems incorrect is that with an ivar you get encapsulation where with a property you don&#39;t.  Just define the property in a class continuation.  This will hide the property from outsiders.  You can also declare the property readonly in the interface and redefine it as readwrite in the implementation like:

    // readonly for outsiders
    @property (nonatomic, copy, readonly) NSString * name;

and have in the class continuation:

    // readwrite within this file
    @property (nonatomic, copy) NSString * name;

To have it completely &quot;private&quot; only declare it in the class continuation.

Why would you use an ivar?

I am trying to make a new line in Xcode 4.2 UITextView, and when I do alt+return, it goes to the next line, but does not show up when built and ran.

How to make a new line in UITextView in nib/storyboard?

I am making an app that processes sensitive credit card data.

If my code is running in debug mode I want to log this data to the console and make some file dumps.   

However on the final appstore version (ie when it is running in release mode) it is essential all of this is disabled (security hazard)!

I will try to answer my question as best I can;  so the question becomes *&#39;Is this solution path the right or best way to do it?&#39;*
  
    // add `IS_DEBUG=1` to your debug build preprocessor settings  
  
    #if( IS_DEBUG )  
    #define MYLog(args...) NSLog(args)  
    #else  
    #define MYLog(args...)  
    #endif  



How to determine whether code is running in DEBUG / RELEASE build?

What are the **main differences** between using Storyboards and xib files.

  Specifically,
 what are the **advantages or disadvantages** of using a Storyboard?

  Unfortunately, despite doing quite a bit of research, all I&#39;ve been able to find on Storyboards are simple tutorials that show you how to set up a Storyboard, instead of concrete information explaining what they are.

What are the benefits of using Storyboards instead of xib files in iOS programming?

On a debug build in Xcode, regardless of whether I am using the simulator or an actual device, NSLog, printf, fprintf assert and NSAssert statements come out on the console

If I now run a release build on the device (say I send a test flight build and big it up on my iPhone; this will be a release build), which of these (if any) are getting recorded?

And how do I retrieve the log?

Does NSLog actually output something on release build?   What is the determining factor? Whether it is writing to stdout or stderr?   is only stderr written to device log?   Does this mean I have to use fprintf?   Is ANYTHING written to device log?  is there even such a thing?  If so, how to pick it up?

Could someone clarify the situation? 

Logging data on device and retrieving the log

I got this problem: &quot;warning: iPad: Icon-72.png: icon dimensions (0 x 0) don&#39;t meet the size requirements.  The icon file must be 72x72 pixels, in .png format (-19014)&quot; when build for archive the iPad only app.
Have checked, my icon is 72x72 pixels. Also checked on info.plist file, the key CFBundleIconFiles already there. Before this have no problem to submit the app. After rejected by app review I want to resubmit (no changes has been made on my Xcode project) but the error appear. Does it because of I&#39;ve upgraded to Mac OSX Lion 10.7.3? (I just update to Mac OSX Lion 10.7.3 before resubmit the app).

Wonder why does the warning says &quot;icon dimensions (0 x 0)&quot;.

Please help me. Thanks.

warning: iPad: Icon-72.png: icon dimensions (0 x 0)

For the most part with ARC (Automatic Reference Counting), we don&#39;t need to think about memory management at all with Objective-C objects. It is not permitted to create `NSAutoreleasePool`s anymore, however there is a new syntax:

    @autoreleasepool {
        …
    }

My question is, why would I ever need this when I&#39;m not supposed to be manually releasing/autoreleasing ?


----------


**EDIT:** To sum up what I got out of all the anwers and comments succinctly:

**New Syntax:**

`@autoreleasepool { … }` is new syntax for

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    …
    [pool drain];

**More importantly:**

 - ARC uses `autorelease` as well as `release`.
 - It needs an auto release pool in place to do so.
 - ARC doesn&#39;t create the auto release pool for you. *However:*
  - The main thread of every Cocoa app already has an autorelease pool in it.
 - There are two occasions when you might want to make use of `@autoreleasepool`:
  1. When you are in a secondary thread and there is no auto release pool, you must make your own to prevent leaks, such as `myRunLoop(…) { @autoreleasepool { … } return success; }`.
  2. When you wish to create a more local pool, as @mattjgalloway has shown in his answer.




Why is @autoreleasepool still needed with ARC?

What&#39;s the exact reason for using dispatch_once in the shared instance accessor of a singleton under ARC?

    + (MyClass *)sharedInstance
    {
        //  Static local predicate must be initialized to 0
        static MyClass *sharedInstance = nil;
        static dispatch_once_t onceToken = 0;
        dispatch_once(&amp;onceToken, ^{
            sharedInstance = [[MyClass alloc] init];
            // Do any other initialisation stuff here
        });
        return sharedInstance;
    }

Isn&#39;t it a bad idea to instantiate the singleton asynchronously in the background? I mean what happens if I request that shared instance and rely on it immediately, but dispatch_once takes until Christmas to create my object? It doesn&#39;t return immediately right? At least that seems to be the whole point of Grand Central Dispatch.

So why are they doing this?

Why does Apple recommend to use dispatch_once for implementing the singleton pattern under ARC?

I am new to iOS5 development and using objective-c. I have trouble understanding the difference between **strong** and **weak** storage.  I have read the documentation and other SO questions, but they all sound identical to me with no further insight.

I read [the documentation: Transitioning To ARC][1] - it references to iOS4 terms of retain, assign, and release; which confuses me. Then I look into Open U CS193p, where it differentiates strong and weak:

&gt; **Strong**: &quot;keep this in the heap until I don&#39;t point to it anymore&quot;&lt;br/&gt;
&gt; **Weak**: &quot;keep this as long as someone else points to it strongly&quot;

Aren&#39;t the two definition identical = if pointer no longer pointing to an object, then free the memory holding the object? I understand the concept of pointers, heap, allocation or deallocation of memory - but what&#39;s the difference between strong and weak? 



  [1]: https://developer.apple.com/library/ios/#releasenotes/ObjectiveC/RN-TransitioningToARC/_index.html

Explanation of strong and weak storage in iOS5

I need to store weak references to objects in an NSArray, in order to prevent retain cycles. I&#39;m not sure of the proper syntax to use. Is this the correct way?

    Foo* foo1 = [[Foo alloc] init];
    Foo* foo2 = [[Foo alloc] init];
    
    __unsafe_unretained Foo* weakFoo1 = foo1;
    __unsafe_unretained Foo* weakFoo2 = foo2;
    
    NSArray* someArray = [NSArray arrayWithObjects:weakFoo1, weakFoo2, nil];

**Note that I need to support iOS 4.x**, thus the `__unsafe_unretained` instead of `__weak`.


----------
**EDIT** (2015-02-18):

For those wanting to use true `__weak` pointers (not `__unsafe_unretained`), please check out this question instead: [Collections of zeroing weak references under ARC][1]


  [1]: https://stackoverflow.com/q/14209070/245265

NSArray of weak references (__unsafe_unretained) to objects under ARC

Can someone explain to me in detail when I must use each attribute: `nonatomic`, `copy`, `strong`, `weak`, and so on, for a declared property, and explain what each does? Some sort of example would be great also. I am using ARC.

Content Type	Original Author	Original Content on Stackoverflow
Question	hollow7	View Question on Stackoverflow
Solution 1 - Objective C	Morothar	View Answer on Stackoverflow
Solution 2 - Objective C	Ashish	View Answer on Stackoverflow
Solution 3 - Objective C	SnowboardBruin	View Answer on Stackoverflow
Solution 4 - Objective C	rhalgravez	View Answer on Stackoverflow

How to enable/disable ARC in an xcode project?

Objective C Problem Overview

Objective C Solutions

Solution 1 - Objective C

Solution 2 - Objective C

Solution 3 - Objective C

Solution 4 - Objective C

Current view controller from AppDelegate?

How to SELECT WHERE NOT EXIST using LINQ?

Attributions