Interoperability With Both World

Intro

Swift designed to pervoide seamless compatibility with Cocoa and objective-c . you can use objective c api in swift as well . its a powerful tool to integrate into you workflow.

Start from Import

import Foundation

This Statement will import statement access all of Foundation’s classes, protocols, methods, properties, and constants. The Process of importing can have following effects

• objective-c type to their equivalent in swift like id to Any
• Objective-C core types to their alternatives in Swift, like NSString to String
• Objective-C concepts to matching concepts in Swift, like pointers to optionals

NOTE

You cannot import C++ code directly into Swift. Instead, create an Objective-C or C wrapper for C++ code

Alongside these Swift modules are generated Objective-C headers.These headers vend the APIs that can be mapped back to Objective-C. Some Swift APIs do not map back to Objective-C because they leverage language features that are not available in Objective-C.

initialization

obj-c initialisation begin with init or initwith: When an Objective-C initializer is imported by Swift, the init prefix becomes an init keyword to indicate swift initializer. objc initializer

-(instancetype)init;
-(instancetype)initWithFrame:(CGRect)frame style:(UITableViewStyle)style;

swift equivalent swift initializer

init(){}
init(frame:CGRect, style: UITableViewStyle){}

if you go through these 2 styles of syntax you will find don’t need to call alloc Swift handles this for you. Notice also that init doesn’t appear anywhere when calling the Swift-style initializer.

Example

objc UITableView *myTableView = [[UITableView alloc] initWithFrame:CGRectZero style:UITableViewStyleGrouped]; swift let myTableView: UITableView = UITableView(frame: .zero, style: .grouped)

Failable Initialization

In objc initalizer directly return the object they initialize. or when initialiser failed an it return nil. in swift the patten built into a language feature called failable initialization.

if you want to design you own you can choose You can indicate whether initializers in your own Objective-C classes can fail using nullability annotations .

nullability annotation

1. indicate whether objc/c pointer can be nil
2. better Communicates the intent of apis
3. allow better static checking
4. improves usages in apis in swift

• Types declared to be nonnullable, either with a _Nonnull annotation or in an audited region, are imported by Swift as a nonoptional.
• Types declared to be nullable with a _Nullable annotation, are imported by Swift as an optional.
• Types declared without a nullability annotation are imported by Swift as an implicitly unwrapped optional

[tableView deselectRowAtIndexPath: nil animated: false]; these api is you pass nil new warnings for nonnull parameters.

example

UIImage(contentsOfFile:) initialize can fail to initialize a UIImage object if an image file doesn’t exist at the provided path. You can use optional binding to unwrap the result of a failable initializer if initialization is successful

Accessing Properties

Objective-C property  declarations using the @property syntax are imported as Swift properties in the following way:

• Properties with the nullability property attributes (nonnull, nullable, and null_resettable) are imported as Swift properties with optional or nonoptional type
• Properties with the readonly property attribute are imported as Swift computed properties with a getter ({ get })
• Properties with the weak property attribute are imported as Swift properties marked with the weak keyword (weak var)
• Properties with an ownership property attribute other than weak (that is, assign, copy, strong, or unsafe_unretained) are imported as Swift properties with the appropriate storage
• Properties with the class property attribute are imported as Swift type properties
• Atomicity property attributes (atomic and nonatomic) are not reflected in the corresponding Swift property declaration, but the atomicity guarantees of the Objective-C implementation still hold when the imported property is accessed from Swift
• Accessor property attributes (getter= and setter=) are ignored by Swift

  Working With Methods

  obj-c method calls like this [myTableView insertSubview:mySubview atIndex:2]; in swift these calls are like this myTableView.insertSubview(mySubview, at: 2) If you’re calling a method with no arguments, you must still include parentheses. myTableView.layoutIfNeeded()

ID Compatibility

1. the Obj-c id type is imported by swift as Any.
2. the compiler introduces a universal bridging conversion operation when a Swift value or object is passed into Objective-C as an id parameter.
3. When id values are imported into Swift as Any, the runtime automatically handles bridging back to either class references or Swift value types.

DownCasting Any

Any means any type downcast any type is not guaranteed to succesed . so we have to use (as?) or if certain about of the object you force downcast the object (as!) instead . if force Downcast the object fails a runtime error is trigger . —–

Want to see something else added? Open an issue.