iOS Cheatsheet

A quick reference cheat sheet for iOS developers so that you turn coffee into code much faster:)

Note: The Avocarrot team will do its best to keep this cheatsheet updated but feel free to send your pull requests if you want to add a new entry or edit something.

##Contents

###Objective-C Basics

• Classes
• Methods
• Operators
• Properties
• Constants
• Flow control statements
• Delegates
• Blocks

###Foundation Framework Classes

• NSString
• NSArray
• NSDictionary
• Objective-C Literals

###C Related Code

• Enumerated Types

##Objective-C Basics

###Classes

####Class header

@interface Human : NSObject

// Define properties and methods

@end

####Class implementation

#import "Human.h"

@interface Human ()
// Define private properties and methods
@end

@implementation Human {
// Define private instance variables
}

// Provide method implementation code

@end

####Creating an instance

Human * anObject = [[Human alloc] init];

###Methods

####Defining methods

// Returns nothing and has no arguments
- (void)foo;

// Returns an NSString object and takes one argument of type NSObject
- (NSString *)fooWithArgument:(NSObject *)bar;

// Takes two arguments one of type NSObject and a second one of type NSString
- (void)fooWithArgument:(NSObject *)bar andArgument:(NSString *)baz;

// Defines a class method (note the + sign)
+ (void)aClassMethod;

####Implementing methods

- (NSString *)fooWithArgument:(NSObject *)bar{
    // Do something here
    return retValue;
}

####Calling a method

[anObject someMethod];
[anObject someMethodWithArg1:arg1 andArg2:arg2];

Operators

Arithmetic Operators

Operator	Description

• | Addition

• | Subtraction

• | Multiplication / | Division % | Modulo

Comparison Operators

Operator	Description
x == y	Returns true if x is equal to y
x > y	Returns true if x is greater than y
x >= y	Returns true if x is greater than or equal to y
x < y	Returns true if x is less than y
x <= y	Returns true if x is less than or equal to y
x != y	Returns true if x is not equal to y

Logical Operators

Operator	Description
!	NOT
&&	Logical AND
||	Logical OR

Compound Assignment Operators

Operator	Description
x += y	Add x to y and place result in x
x -= y	Subtract y from x and place result in x
x *= y	Multiply x by y and place result in x
x /= y	Divide x by y and place result in x
x %= y	Perform Modulo on x and y and place result in x
x &= y	Assign to x the result of logical AND operation on x and y
x	= y
x ^= y	Assign to x the result of logical Exclusive OR on x and y

Bitwise Operators

Operator	Description
&	Bitwise AND
|	Bitwise Inclusive OR
^	Exclusive OR
~	Bit inversion
<<	Shift Left

| Shift Right

Other operators

Operator	Description
()	Cast
? :	Ternary
&	Memory Address

• | Pointer

###Properties

####Define properties

@property (attribute1, attribute2) NSString *aProperty;

Attribute Type	Purpose
strong (iOS 4 = retain) (default)	Creates an owning relationship to the object that is assigned to the property
weak (iOS 4 = unsafe_unretained)	Creates a non-owning relationship
assign (default)	Normal assign, doesn’t perform any kind of memory-management
copy	Make an immutable copy of the object upon assignment
atomic (default)	Only allows one thread to access the property, which makes it threadsafe
nonatomic	Allows multiple threads to access the property simultaneously, which makes it not threadsafe
readwrite (default)	Generates both getter and setter
readonly	Generates only getter
getter=method	Use this to specify a different name for the property's getter method
setter=method	Use this to specify a different name for the property's setter method

####Access Properties

[anObject aProperty];

// Alternative
anObject.aProperty

###Constants

####Preprocessing Macros

This is not an actual constant because it defines a macro which replaces all occurrences of MAX_NUMBER_OF_ITEMS with the actual value before compile time.

#define MAX_NUMBER_OF_ITEMS 10

####Using const

A better approach is to use const.

NSString *const kMyName = @"Clark";

####Static and extern

If you know that the constant will only be available within it's implementation file, then you can use static. Using static means that the constant will only be available in that file.

static NSString * const kMyName = @"Clark";

If you want to have a constant global then you should use extern.

// .h file
extern NSString * const kMyName;

// .m file
NSString * const kMyName = @"Clark";

###Flow control statements

####If-else statement

if (someCondition) {
    // Execute if the condition is true
} else if (someOtherCondition) {
    // Execute if the other condition is true
} else {
    // Execute if the none of the above conditions are true
}

####Ternary operator

someCondition ? @"True" : @"False";

####For Loops

for (int i = 0; i < totalCount; i++) {
    // Do something here
}

####While Loop

while (someCondition) {
   // Do something here
}

####Do While Loop

do {
    // Do something here
} while (someCondition);

####Switch

switch (aLabel)
{
    case kLabelA:
        // Execute this if matched
        break;

     case kLabelB:
        // Execute this if matched
        break;

     default:
        // Execute this if matched
        break;
}

###Delegates

Delegates are a design pattern. A delegate allows one object to send messages to another object when an event happens. Check out [Apple docs](https:// developer.apple.com/library/ios/documentation/general/conceptual/CocoaEncyclopedia/DelegatesandDataSources/DelegatesandDataSources.html):

####Become the delegate of a framework class

Step 1

Declare that your class adopts the protocol in the class definition in the angled brackets after the class/superclass name.

// MyTableViewController.h

@interface MyTableViewController : UIViewController <UITableViewDelegate, UITableViewDataSource>

@end

Step 2

Set your object as the delegate.

// MyTableViewController.m

[tableView setDelegate:self];

@end

Step 3

Implement the delegate methods.

####Implement your own delegate for a custom class

Step 1

Declare the protocol methods

// Superman.h
#import <Foundation/Foundation.h>

@protocol SupermanDelegate <NSObject>

- (void)dodgeBullet;
- (void)seeThroughThings;
- (void)fly;

@optional
- (void)eat;

@end

@interface Superman : NSObject

// Create a property for the delegate reference
@property (nonatomic, weak) id <SupermanDelegate> delegate;

// Define other methods and properties

@end

Step 2

Set the delegate object

// Superman.m

[self setDelegate:anObject];

Step 3

Start sending delegate messages

// Superman.m

[self.delegate fly];

For the delegate methods that are optional, it is wise to check if the delegate can respond to that method before firing.

if ([self.delegate respondsToSelector:@selector(eat)]) {
  [self.delegate eat];
}

Blocks

Blocks are a language-level feature added to C, Objective-C and C++, which allow you to create distinct segments of code that can be passed around to methods or functions as if they were values.

For more information see [Programming with Objective-C - Working with Blocks](https:// developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithBlocks/WorkingwithBlocks.html)

To declare a block local variable:

returnType (^blockName)(parameterTypes) = ^returnType(parameters) {...};

To declare a block property:

@property (nonatomic, copy) returnType (^blockName)(parameterTypes);

To accept a block as a method parameter:

- (void)aMethodThatTakesABlock:(returnType (^)(parameterTypes))blockName;

To pass a block as an argument in a method call:

[someObject someMethodThatTakesABlock: ^returnType (parameters) {...}];

To define a block type:

typedef returnType (^TypeName)(parameterTypes);
TypeName blockName = ^returnType(parameters) {...};

##Class Specific

###NSString

####Quick examples

NSString *firstName = @"Clark";
NSString *lastName = @"Kent";
NSString *fullName = [NSString stringWithFormat:  @"My full name is %@ %@",  firstName, lastName];

####NSString format specifier

Specifier	Description
%@	Objective-C object
%zd	NSInteger
%lx, (long)	CFIndex
%tu	NSUInteger
%i	int
%u	unsigned int
%hi	short
%hu	unsigned short
%%	Literal %

###NSArray

####Quick examples

// Create an array
NSMutableArray *anArray = [@[@"Clark Kent", @"Lois Lane"] mutableCopy];

// Add new items
[anArray addObject:@"Lex Luthor"];

// Find array length
NSLog(@"Array has %d items", [anArray count]);

// Iterate over array items
for (NSString *person in anArray) {
 NSLog(@"Person: %@", person);
}

// Access item with index
NSString *superman = anArray[0];

// Remove Object @"Clark Kent"
[anArray removeObject:@"Clark Kent"];

// Remove the first Object
[anArray removeObjectAtIndex:0];

###NSDictionary

####Quick examples

// Create a dictionary
NSMutableDictionary *person = [@{
                             @"firstname" : @"Clark",
                             @"lastname" : @"Kent",
                             @"age" : [NSNumber numberWithInt:35]
                             } mutableCopy];

// Access values
NSLog(@"Superman's first name is %@", person[@"firstname"]);
// or
NSLog(@"Superman's first name is %@", [person objectForKey:@"firstname"]);

// Find number of items in dictionary
[person count];

// Add an object to a dictionary
[person setObject:@"job" forKey:@"teacher"];

// Remove an object to a dictionary
[person removeObjectForKey:@"firstname"];

##Objective-C Literals

Available from LLVM Compiler version 4.0 made available with Xcode 4.4

###Strings

NSString *string = @"This is a string.";

###Numbers

NSNumber *number = @126;      // int          : Equal to [NSNumber numberWithInt:126];
NSNumber *number = @126u;     // unsigned int : Equal to [NSNumber numberWithUnsignedInt:126u];
NSNumber *number = @126l;     // long         : Equal to [NSNumber numberWithLong:126l];
NSNumber *number = @126.544f; // float        : Equal to [NSNumber numberWithFloat:126.544f]
NSNumber *number = @126.544;  // double       : Equal to [NSNumber numberWithDouble:126.544]
NSNumber *number = @YES;      // bool         : Equal to [NSNumber numberWithBool:YES]

###Containers

NSArray *array = @[object1,object2,object3]; // Creating NSArray
Object *object2 = array[1]; // Accessing NSArray
mutableArray[1] = newObject; // Adding to NSMutableArray

NSDictionary *dictionary = @{ @"key1" : object1, @"key2" : object2, @"key3" : object3 }; // Creating NSDictionary
Object *object2 = dictionary[@"key2"]; // Accessing NSDictionary
mutableDictionary[@"name"] = @"Henry"; // Adding to NSMutableDictionary

##C References

###Enumerated Types

####Apple's Examples

Each enumerate is given a corresponding integer value, so

typedef NS_ENUM(NSInteger, UIButtonType) {
   UIButtonTypeCustom,
   UIButtonTypeSystem,
   UIButtonTypeDetailDisclosure,
   UIButtonTypeInfoLight,
   UIButtonTypeInfoDark,
   UIButtonTypeContactAdd,
   UIButtonTypeRoundedRect
};

is the same as

typedef NS_ENUM(NSInteger, UIButtonType) {
   UIButtonTypeCustom = 0,
   UIButtonTypeSystem = 1,
   UIButtonTypeDetailDisclosure = 2,
   UIButtonTypeInfoLight = 3,
   UIButtonTypeInfoDark = 4,
   UIButtonTypeContactAdd = 5,
   UIButtonTypeRoundedRect = 6
};

Explicitly defining the first enumerate's value is not required and it will default to 0.

####Using an enumerated type

UIButton *button = [UIButton buttonWithType:UIButtonTypeInfoLight];

Or create a variable to pass into the methods like so...

UIButtonType myButtonType = UIButtonTypeCustom;
UIButton *myButton = [UIButton buttonWithType:myButtonType];

Because they are not objects, you must print enumerated types as integers

UIButtonType myButtonType = UIButtonTypeRoundedRect;

// Bad, will give you a warning and might even crash
NSLog(@"%@", myButtonType);

// Good, will properly print the value as an integer
NSLog(@"%d", myButtonType);