A few code snippets from my Xcode arsenal

How do I convert an NSString value to NSData?

How do I convert an NSString value to NSData?

Source: (StackOverflow)

Creating an abstract class in Objective C

I'm originally a Java programmer who now works with Objective-C. I'd like to create an abstract class but that doesn't appear to be possible in Objective-C. Is this possible?

If not, how close to an abstract class can I get in Objective-C?

Source: (StackOverflow)

Constants in Objective-C

I'm developing a Cocoa application, and I'm using constant NSStrings as ways to store key names for my preferences.

I understand this is a good idea, because it allows easy changing of keys if necessary. Plus, it's the whole 'separate your data from your logic' notion.

Anyway, is there a good way to make these constants defined once for the whole application? I'm sure that there's an easy and intelligent way, but right now my classes just redefine the ones they use.

Source: (StackOverflow)

How do I set up NSZombieEnabled in Xcode 4?

How do I set up NSZombieEnabled and CFZombieLevel for my executable in Xcode 4?

Source: (StackOverflow)

How do I create a basic UIButton programmatically?

How can I create a basic UIButton programmatically? For example in my view controller, when executing the viewDidLoad method, three UIButtons will be created dynamically and its layout or properties are set.

Source: (StackOverflow)

What's the difference between the atomic and nonatomic attributes?

What do atomic and nonatomic mean in property declarations?

@property(nonatomic, retain) UITextField *userName;
@property(atomic, retain) UITextField *userName;
@property(retain) UITextField *userName;

What is the operational difference between these three?

Source: (StackOverflow)

How can I disable ARC for a single file in a project?

I am using ARC successfully in my project. However, I have encountered a few files (e.g., in unit tests and mock objects) where the rules of ARC are a little more fragile right now. I recall hearing that there was a way to disable ARC on a per-file basis, though I have been unable to find this option.

Is this possible? How do I disable ARC on a per-file basis?

Source: (StackOverflow)

performSelector may cause a leak because its selector is unknown

I'm getting the following warning by the ARC compiler:

"performSelector may cause a leak because its selector is unknown".

Here's what I'm doing:

[_controller performSelector:NSSelectorFromString(@"someMethod")];

Why do I get this warning? I understand the compiler can't check if the selector exists or not, but why would that cause a leak? And how can I change my code so that I don't get this warning anymore?

Source: (StackOverflow)

What is a typedef enum in Objective-C?

I don't think I fundamentally understand what an enum is, and when to use it.

For example:

typedef enum {
} ShapeType;

What is really being declared here?

Source: (StackOverflow)

Shortcuts in Objective-C to concatenate NSStrings

Are there any shortcuts to (stringByAppendingString:) string concatenation in Objective-C, or shortcuts for working with NSString in general?

For example, I'd like to make

NSString *myString = @"This";
NSString *test = [myString stringByAppendingString:@" is just a test"];

something more like

string myString = "This";
string test = myString + " is just a test";

Source: (StackOverflow)

How to convert an NSString into an NSNumber

How can I convert a NSString containing a number of any primitive data type (e.g. int, float, char, unsigned int, etc.)? The problem is, I don't know which number type the string will contain at runtime.

I have an idea how to do it, but I'm not sure if this works with any type, also unsigned and floating point values:

long long scannedNumber;
NSScanner *scanner = [NSScanner scannerWithString:aString];
[scanner scanLongLong:&scannedNumber]; 
NSNumber *number = [NSNumber numberWithLongLong: scannedNumber];

Thanks for the help.

Source: (StackOverflow)

How do you trigger a block after a delay, like -performSelector:withObject:afterDelay:?

Is there a way to call a block with a primitive parameter after a delay, like using performSelector:withObject:afterDelay: but with an argument like int/double/float?

Source: (StackOverflow)

@synthesize vs @dynamic, what are the differences?

What are the differences between implementing a @property with @dynamic or @synthesize?

Source: (StackOverflow)

How do I test if a string is empty in Objective C?

How do I test if an NSString is empty in Objective C?

Source: (StackOverflow)