Objective-C和Swift的转换速查手册(推荐)

    前言

    如果你正要从Objective-C过渡到Swift,或反过来,一个在两种语言间显示等效代码的小手册会很有帮助。本文内容就是这些:苹果开发者的红宝书,包含变量,集合,函数,类等等。

    下面例子中,上面是Objective-C代码,下面是等效的Swift代码。必要的地方我会给一些备注来帮助你理解。

    变量与常量

    创建一个变量

    
    //Objective-C
    NSInteger score = 556;
    //
    NSString *name = @"Taylor";
    //
    BOOL loggedIn = NO;
    
    //Swift
    var score = 556
    //
    var name = "Taylor"
    //
    var loggedIn = false

    创建一个常量

    
    //Objective-C
    const NSInteger score = 556;
    //
    NSString * const name = @"Taylor";
    //
    const BOOL firstRun = YES;
    //Objective-C中常量用的很少
    
    //Swift
    let score = 556
    //
    let name = "Taylor"
    //
    let firstRun = true
    //Swift中常量很常见

    创建一个变量数组

    创建一个常量数组

    
    //Objective-C
    NSArray *grades = @[@90, @85, @97];
    //
    NSArray *names = @[@"Taylor", @"Adele", @"Justin"];
    
    //Swift
    let grades = [90, 85, 97]
    //
    let names = ["Taylor", "Adele", "Justin"]

    向数组中添加一个值类型

    
    //Objective-C
    NSMutableArray *array = [NSMutableArray new];
    //
    [array addObject:[NSValue valueWithRect:CGRectMake(0, 0, 32, 64)]];
    //在添加到集合前,值类型有对应的引用类型
    
    //Swift
    var array = [CGRect]()
    //
    array.append(CGRect(x: 0, y: 0, width: 32, height: 64))

    创建一个字典

    
    //Objective-C
    NSDictionary *houseNumbers = @{ @"Paul": @7, @"Jess": @56, @"Peter": @332 };
    
    //Swift
    let houseNumbers = ["Paul": 7, "Jess": 56, "Peter": 332]

    定义一个枚举

    
    //Objective-C
    typedef NS_ENUM(NSInteger, ShapeType) {
     kCircle,
     kRectangle,
     kHexagon
    };
    
    //Swift
    enum ShapeType: Int {
     case circle
     case rectangle
     case hexagon
    }

    附加一串字符

    
    //Objective-C
    NSString *first = @"Hello, ";
    NSString *second = [first stringByAppendingString:@" world!"];
    
    //Swift
    let first = "Hello, "
    let second = first + "world!"

    增加数字

    
    //Objective-C
    NSInteger rating = 4;
    rating++;
    rating += 3;
    
    //Swift
    var rating = 4
    rating += 1
    rating += 3

    插入字符串

    
    //Objective-C
    NSString *account = @"twostraws";
    NSString *str = [NSString stringWithFormat:@"Follow me on Twitter: %@", account];
    
    //Swift
    let account = "twostraws"
    let str = "Follow me on Twitter: \(account)"

    打印调试信息

    
    //Objective-C
    NSString *username = @"twostraws";
    NSLog(@"Username is %@", username);
    
    //Swift
    let username = "twostraws"
    print("Username is \(username)")

    控制流

    检查状态

    
    //Objective-C
    NSInteger result = 86;
    if (result >= 85) {
     NSLog(@"You passed the test!");
    } else {
     NSLog(@"Please try again.");
    }
    
    //Swift
    let result = 86
    
    if result >= 85 {
     print("You passed the test!")
    } else {
     print("Please try again.")
    }

    循环一定次数

    
    //Objective-C
    for (NSInteger i = 0; i < 100; ++i) {
     NSLog(@"This will be printed 100 times.");
    }
    
    //Swift
    for _ in 0 ..< 100 {
     print("This will be printed 100 times.")
    }

    在数组中循环

    
    //Objective-C
    NSArray *companies = @[@"Apple", @"Facebook", @"Twitter"];
    
    for (NSString *name in companies) {
     NSLog(@"%@ is a well-known tech company.", name);
    }
    
    //Swift
    let companies = ["Apple", "Facebook", "Twitter"]
    
    for name in companies {
     print("\(name) is a well-known tech company.")
    }

    数值切换

    
    //Objective-C
    NSInteger rating = 8;
    
    switch (rating) {
     case 0 ... 3:
     NSLog(@"Awful");
     break;
     case 4 ... 7:
     NSLog(@"OK");
     break;
     case 8 ... 10:
     NSLog(@"Good");
     break;
     default:
     NSLog(@"Invalid rating.");
    }
    //很多人不知道Objective-C有范围支持,所以你也许看到二选一的语法
    
    //Swift
    let rating = 8
    
    switch rating {
    case 0...3:
     print("Awful")
    case 4...7:
     print("OK")
    case 8...10:
     print("Good")
    default:
     print("Invalid rating.")
    }
    //Swift不会fall through案例,除非你使用fallthrough关键字

    函数

    不接收参数也没有返回的函数

    
    //Objective-C
    - (void)printGreeting {
     NSLog(@"Hello!");
    }
    
    [self printGreeting];
    
    //Swift
    func printGreeting() {
     print("Hello!")
    }
    
    printGreeting()

    不接收参数,返回一个字符串的函数

    
    //Objective-C
    - (NSString*)printGreeting {
     return @"Hello!";
    }
    
    NSString *result = [self printGreeting];
    
    //Swift
    func printGreeting() -> String {
     return "Hello!"
    }
    
    let result = printGreeting()

    接收一个字符串,返回一个字符串的函数

    
    //Objective-C
    - (NSString*)printGreetingFor:(NSString*)user {
     return [NSString stringWithFormat:@"Hello, %@!", user];
    }
    
    NSString *result = [self printGreetingFor:@"Paul"];
    //第一个参数的名称需要为方法名的一部分
    
    //Swift
    func printGreeting(for user: String) -> String {
     return "Hello, \(user)!"
    }
    
    let result = printGreeting(for: "Paul")

    接收一个字符串和一个整数,返回一个字符串的函数

    
    //Objective-C
    - (NSString*)printGreetingFor:(NSString*)user withAge:(NSInteger)age {
     if (age >= 18) {
      return [NSString stringWithFormat:@"Hello, %@! You're an adult.", user];
     } else {
      return [NSString stringWithFormat:@"Hello, %@! You're a child.", user];
     }
    }
    
    NSString *result = [self printGreetingFor:@"Paul" withAge:38];
    
    //Swift
    func printGreeting(for user: String, age: Int) -> String {
     if age >= 18 {
      return "Hello, \(user) You're an adult."
     } else {
      return "Hello, \(user)! You're a child."
     }
    }
    
    let result = printGreeting(for: "Paul", age: 38)

    从函数返回多个值

    
    //Objective-C
    - (NSDictionary*)loadAddress {
     return @{
      @"house": @"65, Park Street",
      @"city": @"Bristol",
      @"country": @"UK"
     };
    }
    
    NSDictionary*address = [self loadAddress];
    NSString *house = address[@"house"];
    NSString *city = address[@"city"];
    NSString *country = address[@"country"];
    //Objective-C不支持元祖(tuple),所以用字典或数组替代
    
    //Swift
    func loadAddress() -> (house: String, city: String, country: String) {
     return ("65, Park Street", "Bristol", "UK")
    }
    
    let (city, street, country) = loadAddress()

    不接收参数没有返回的闭环

    
    //Objective-C
    void (^printUniversalGreeting)(void) = ^{
     NSLog(@"Bah-weep-graaaaagnah wheep nini bong");
    };
    
    printUniversalGreeting();
    
    //Swift
    let universalGreeting = {
     print("Bah-weep-graaaaagnah wheep nini bong")
    }
    
    universalGreeting()

    不接收参数返回一个字符串的闭环

    
    //Objective-C
    NSString* (^getUniversalGreeting)(void) = ^{
     return @"Bah-weep-graaaaagnah wheep nini bong";
    };
    
    NSString *greeting = getUniversalGreeting();
    NSLog(@"%@", greeting);
    
    //Swift
    let getUniversalGreeting = {
     return "Bah-weep-graaaaagnah wheep nini bong"
    }
    
    let greeting = getUniversalGreeting()
    print(greeting)

    接收一个字符串参数,返回一个字符串的闭环

    
    //Objective-C
    NSString* (^getGreeting)(NSString *) = ^(NSString *name) {
     return [NSString stringWithFormat:@"Live long and prosper, %@.", name];
    };
    
    NSString *greeting = getGreeting(@"Paul");
    NSLog(@"%@", greeting);
    
    //Swift
    let getGreeting = { (name: String) in
     return "Live long and prosper, \(name)."
    }
    
    let greeting = getGreeting("Paul")
    print(greeting)

    创建空类

    
    //Objective-C
    @interface MyClass : NSObject
    @end
    
    @implementation MyClass
    @end
    
    //Swift
    class MyClass: NSObject {
    }
    //推荐使用结构代替类,这样也许不需要从NSObject继承了

    创建有2个属性的类

    
    //Objective-C
    @interface User : NSObject
    @property (nonatomic, copy) NSString *name;
    @property (nonatomic, assign) NSInteger age;
    @end
    
    @implementation User
    
    @end
    
    //Swift
    class User {
     var name: String
     var age: Int
     
     init(name: String, age: Int) {
      self.name = name
      self.age = age
     }
    }
    //Swift要求进行初始化,给这些属性默认值

    创建有一个私有属性的类

    
    //Objective-C
    //在头文件中
    @interface User : NSObject
    @property (nonatomic, copy) NSString *name;
    @end
    
    //在执行文件中
    @interface User()
    @property (nonatomic, assign) NSInteger age;
    @end
    
    @implementation User
    
    @end
    //Objective-C实际上并不支持私有属性,通常都用这种变通方式
    
    //Swift
    class User {
     var name: String
     private var age: Int
     
     init(name: String, age: Int) {
      self.name = name
      self.age = age
     }
    }

    创建有一个实例方法的类

    
    //Objective-C
    @interface Civilization : NSObject
    - (NSInteger)getMeaningOfLife;
    @end
    
    @implementation Civilization
    - (NSInteger)getMeaningOfLife {
     return 42;
    }
    @end
    
    //Swift
    class Civilization {
     func getMeaningOfLife() -> Int {
      return 42
     }
    }

    创建有一个静态方法的类

    
    //Objective-C
    @interface Civilization : NSObject
    + (NSInteger)getMeaningOfLife;
    @end
    
    @implementation Civilization
    + (NSInteger)getMeaningOfLife {
     return 42;
    }
    @end
    //差别很小,用+而不是-
    
    //Swift
    class Civilization {
     class func getMeaningOfLife() -> Int {
      return 42
     }
    }
    //Swift也支持静态方法——它不会在子类中被覆盖

    用一种新方法扩展一个类型

    
    //Objective-C
    @interface NSString (Trimming)
    - (NSString*)trimmed;
    @end
    
    @implementation NSString (Trimming)
    
    - (NSString*)trimmed {
     return [self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    }
    
    @end
    
    //Swift
    extension String {
     func trimmed() -> String {
      return trimmingCharacters(in: .whitespacesAndNewlines)
     }
    }

    检查一个对象的类

    
    //Objective-C
    if ([object isKindOfClass:[YourClass class]]) {
     NSLog(@"This is a YourClass.");
    }
    
    //Swift
    if object is YourClass {
     print("This is a YourClass.")
    }

    类型转换

    
    //Objective-C
    Dog *poodle = (Dog*)animalObject;
    
    //Swift
    let poodle = animalObject as? Dog
    //
    let poodle = animalObject as! Dog
    //如果不是一个dog,前者会把poodle设为nil,后者则会崩溃

    GCD

    在不同线程运行代码

    
    //Objective-C
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
     NSLog(@"Running in the background...");
     
     dispatch_async(dispatch_get_main_queue(), ^{
      NSLog(@"Running back on the main thread");
     });
    });
    
    //Swift
    DispatchQueue.global().async {
     print("Running in the background...")
     
     DispatchQueue.main.async {
      print("Running on the main thread")
     }
    }

    总结

    以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作具有一定的参考学习价值,如果有疑问大家可以留言交流,谢谢大家对lingkb的支持。