Contents

Introduction

Swift 最新已经是 2.1 了,更优美了,日趋成熟了,加上公司项目以后可能支持到 iOS7,就可以使用 Swift 写项目了,所以必须学习下了,先看看官方的文档:
Using Swift with Cocoa and Objective-C (Swift 2.1)

Interoperablility : 互动性

  • Initialization

oc 初始化方法,在swift里省去了with,with后面的变成了参数名:

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

init(frame: CGRect, style: UITableViewStyle) { /* ... */ }

oc alloc swift不需要调用,alloc和init一气呵成:

UITableView *myTableView = [[UITableView alloc] initWithFrame:CGRectZero style:UITableViewStyleGrouped];

let myTableView: UITableView = UITableView(frame: CGRectZero, style: .Grouped)
  • Class Factory Methods and Convenience Initializers

oc 工厂方法保留,提供便利性

UIColor *color = [UIColor colorWithRed:0.5 green:0.0 blue:0.5 alpha:1.0];

let color = UIColor(red: 0.5, green: 0.0, blue: 0.5, alpha: 1.0)
  • Failable Initialization

oc 初始化失败返回 nil, swift 把这处理成了一种语言特性,称之为 failable initialization.

if let image = UIImage(contentsOfFile: "MyImage.png") {
// loaded the image successfully
} else {
// could not load the image
}
  • Accessing Properties

    swift property attributes: nonnull,nullable,null_resettable

    readonly: just a getter {get}

    weak: marked with the weak keyword (weak var)

    assign,copy,strong,unsafe_unretained == oc

    atomic / noatomic : are not reflected in swift(没有用了,不过oc导入swift的时候有用)

    getter= / setter= : are ignoerd by swift(忽略了)

    访问属性使用 dot.

  • Working with Methods

swift 里访问 oc 的方法也可以使用 dot.

	oc 方法名被拆开
[myTableView insertSubview:mySubview atIndex:2];
	swift 方法名是oc的第一段剩下的段作为参数名第一个参数并没有参数名
myTableView.insertSubview(mySubview, atIndex: 2)
	对于没有参数的直接带个小括号
myTableView.layoutIfNeeded()
  • id Compatibility

id compatibility 兼容性:swift include an AnyObject type, is similar to oc's id type;保持类的灵活性;

var myObject: AnyObject = UITableViewCell()
myObject = NSDate()

let futureDate = myObject.dateByAddingTimeInterval(10)
let timeSinceNow = myObject.timeIntervalSinceNow

This includes Objective-C compatible methods and properties marked with the @objc attribute.

  • Unrecognized Selectors and Optional Chaining

和 oc 一样的,AnyObject 对象调用方法不会有警告,如果不能响应,在运行时就会crash; For example, the following code compiles without a compiler warning, but triggers an error at runtime:

myObject.characterAtIndex(5)
// crash, myObject doesn't respond to that method

不过 swift 做的很好!!! swift use optionals to guard against such unsafe behavior. swift 使用自选项来规避诸如此类的危险行为。

Accessing a property on AnyObject always returns an optional value. 属性访问总是返回自选值;

  • Downcasting AnyObject

当确定或者能够合理推断时向下转换对象类型; but can not guaranteed to succeed.

不确定的时候用 : as?

let userDefaults = NSUserDefaults.standardUserDefaults()
let lastRefreshDate: AnyObject? = userDefaults.objectForKey("LastRefreshDate")
if let date = lastRefreshDate as? NSDate {
print("\(date.timeIntervalSinceReferenceDate)")
}

确定的时候用: as!

let myDate = lastRefreshDate as! NSDate
let timeInterval = myDate.timeIntervalSinceReferenceDate

如果类型不一致就会报错,有点assert的味道哦

let myDate = lastRefreshDate as! NSString // Error
  • Nullability and Optionals

oc object references can be nil, swift all values--including structures and object references--are guaranteed to be on-null.

value 的 type 是可选的;赋值为 nil 意味着 值的丢失; Instead, you represent a value that could be missing by wrapping the type of the value in an optional type. When you need to indicate that a value is missing, you use the value nil. For more information about optionals, see Optionals in The Swift Programming Language (Swift 2.1).

情形 使用
针对于个人类型: _Nullable / _Nonnull
针对于个人属性: nullable / nonnull / null_resettable
针对于整个区域: NS_ASSUM_NONNULL_BEGIN - NS_ASSUM_NONNULL_END

如果没有相关的信息,swift 就不能区分是不是自选的,并且将作为 an implicitly unwrapped optional.

For example, consider the following Objective-C declarations:

@property (nullable) id nullableProperty;
@property (nonnull) id nonNullProperty;
@property id unannotatedProperty;

NS_ASSUME_NONNULL_BEGIN
- (id)returnsNonNullValue;
- (void)takesNonNullParameter:(id)value;
NS_ASSUME_NONNULL_END

- (nullable id)returnsNullableValue;
- (void)takesNullableParameter:(nullable id)value;

- (id)returnsUnannotatedValue;
- (void)takesUnannotatedParameter:(id)value;

Here’s how they’re imported by Swift:

var nullableProperty: AnyObject?
var nonNullProperty: AnyObject
var unannotatedProperty: AnyObject!

func returnsNonNullValue() -> AnyObject
func takesNonNullParameter(value: AnyObject)

func returnsNullableValue() -> AnyObject?
func takesNullableParameter(value: AnyObject?)

func returnsUnannotatedValue() -> AnyObject!
func takesUnannotatedParameter(value: AnyObject!)
  • Lightweight Generics 轻型、泛型

For example, consider the following Objective-C property declarations:

@property NSArray<NSDate *> *dates;
@property NSSet<NSString *> *words;
@property NSDictionary<NSURL *, NSData *> *cachedData;

Here’s how Swift imports them:

var dates: [NSDate]
var words: Set<String>
var cachedData: [NSURL: NSData]

除了Foundation这些之外,别的会被忽略; Aside from these Foundation collection classes, Objective-C lightweight generics are ignored by Swift.