Objective-C与Swift代码转换速查手册



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    Objective-C 与Swift代码转换速查手册

    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,上边是Objective-C代码,下边是等效的Swift代码。必要的地方我会给一些备注来帮助理解。

    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

    //Objective-C
    NSMutableArray *items = [NSMutableArray new];
    //
    NSMutableArray<NSString *> *results = [NSMutableArray new];
    //Objective-C中的泛型存在争议,这里列了两种形式
    
    //Swift
    var items = [String]()
    //
    var results = Array<String>()
    //强烈推荐用上面那种
    

    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,所以你也许会看到别的语法
    
    
    //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<NSString*, NSString*>*)loadAddress {
        return @{
            @"house": @"65, Park Street",
            @"city": @"Bristol",
            @"country": @"UK"
        };
    }
    
    NSDictionary<NSString*, NSString*> *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包

    //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包

    //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包

    //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")
        }
    }
    

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