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Structure

• You have .h and .m file
• .h files are "Header" files, where you declare functions and variables
• .m files are "Implementation" files, where you implement functions
• You have to import .h files in your .m file
• @property is the keyword for declaring a variable in a .h
• A property is public
• A instance variable is private

Allocation

• To allocate a new objet, you have to follow this syntax: Person *person1 = [[Person alloc] init];

Pointer

• You have to add an * when declaring a new variable, just before the name (for all non-number objects) (i.e: NSString *myStr = @"Hello")

Getter

• You can override the getter of a property in your .m like following: -(type)myproperty{...}
• _myproperty will be the property value

Setter

• You can override the setter of a property in your .m like following: -(void)setMyproperty:(type)myproperty{...}
• myproperty will be the new value
• _mypropertywill be the old value

String

• You have to use the @sign before the string (i.e: @"Test")
• You have to use the format function to construct string with variables (i.e: [NSString stringWithFormat: @"My name is %@!", firstName];)

Number

• You can use int, float or double but if you need to store numbers in an array you have to use NSNumber (i.e: NSNumber *myNum = [NSNumbre numberWithInt:8];)

Dot VS Brackets

• Use dot just for properties (when possible)

Boolean

• Use BOOL type
• Use YES and NO as value
• Always use if (myBool) {} instead of if (myBool == YES) {}
• Always use if (!myBool) {} instead of if (myBool == NO) {}

Methods

• You can declare a function as static with + attribute instead of -

Arrays

• Use NSArray for array initialized with data (you can't modify data)
• Use NSMutableArray for array that should be modified

Atomic vs Nonatomic

• Atomic is thread safe but slower
• Nonatomic is not thread safe but fast

Strong vs Weak

• Strong ensure that the compiler does not destroy the object (until the property receive a nil value)
• Weak is used for delegates, outlets, subviews, controls... It specifie a reference that is strongly referenced by an object. Once the object is destroyed, the weak property is destroyed as well. It avoid retain cycle (memory leak)

Nullability

• _Nullable is the equivalent of ? in Swift
• _Nonnull is the equivalent of ! in Swift

Category and Extension

• A category in Objective-C allows to add features to a Class
• An extension allows is like a category but also allows to modify properties of a class