Objective-C 构造方法的定义和声明规范

总目录 iOS开发笔记目录 从一无所知到入门

源码中 NSArray 的构造方法与命名规律

@interface NSArray<ObjectType> (NSArrayCreation)+ (instancetype)array;
+ (instancetype)arrayWithObject:(ObjectType)anObject;
+ (instancetype)arrayWithObjects:(const ObjectType _Nonnull [_Nonnull])objects count:(NSUInteger)cnt;
+ (instancetype)arrayWithObjects:(ObjectType)firstObj, ... NS_REQUIRES_NIL_TERMINATION;
+ (instancetype)arrayWithArray:(NSArray<ObjectType> *)array;- (instancetype)initWithObjects:(ObjectType)firstObj, ... NS_REQUIRES_NIL_TERMINATION;
- (instancetype)initWithArray:(NSArray<ObjectType> *)array;
- (instancetype)initWithArray:(NSArray<ObjectType> *)array copyItems:(BOOL)flag;/* Reads array stored in NSPropertyList format from the specified url. */
- (nullable NSArray<ObjectType> *)initWithContentsOfURL:(NSURL *)url error:(NSError **)error  API_AVAILABLE(macos(10.13), ios(11.0), watchos(4.0), tvos(11.0));
/* Reads array stored in NSPropertyList format from the specified url. */
+ (nullable NSArray<ObjectType> *)arrayWithContentsOfURL:(NSURL *)url error:(NSError **)error API_AVAILABLE(macos(10.13), ios(11.0), watchos(4.0), tvos(11.0)) NS_SWIFT_UNAVAILABLE("Use initializer instead");@end

可以看出，一个类型中，用于返回一个该类型对象的方法(不止是构造方法)的命名规律为以下(其中Xxx表示具体的类名)：

• 方法的返回值可以从 (Xxx *) 变成 (instancetype) ，其中instancetype在该类中表示该类的实例类型。加nullable表示方法的返回值可为空。
• 以+开头的类方法的命名：xxx xxxWithArg1: arg2: arg3...
• 以-开头的对象方法的命名：initWithArg1: arg2: arg3...

自定义类的构造方法命名

按照上述规律，自定义类，代码如下：

截图

Person类定义：

main方法调用部分：

代码

//
//  main.m
//  构造方法
//
//  Created by wuyujin1997 on 2023/2/23.
//#import <Foundation/Foundation.h>@interface Person : NSObject {@publicNSString* name;int age;
}
+ (instancetype) person;
+ (instancetype) personWithName:(NSString*)name age:(int)age;
- (instancetype) initWithName:(NSString*)name age:(int)age;
@end@implementation Person
+ (instancetype) person {return [Person new];
}
+ (instancetype) personWithName:(NSString*)name age:(int)age {Person* person = [Person new];person->name = name;person->age = age;return person;
}
- (instancetype) initWithName:(NSString*)name age:(int)age {self->name = name;self->age = age;return self;
}
// description方法用于改写打印本类对象时的输出内容格式，类似于 Java 中的 toString() 。
- (NSString *)description {return [NSString stringWithFormat:@"<%@:%p> name:%@ age:%d", [self class], self, self->name, self->age];
}
@endint main(int argc, const char * argv[]) {NSArray* arr1 = [NSArray new];NSArray* arr2 = [NSArray array];NSArray* arr3 = [NSArray arrayWithArray:arr1];Person* p1 = [Person new];Person* p2 = [Person person];Person* p3 = [Person personWithName:@"wuyujin1997" age:26];NSLog(@"%@", p1);NSLog(@"%@", p2);NSLog(@"%@", p3);[p1 initWithName:@"测试赋值" age:22];   // 已有对象，只是调用 initXxx 方法去做属性值的赋值/初始化而已。NSLog(@"%@", p1);return 0;
}

输出

2023-02-26 20:02:19.759434+0800 构造方法[29043:905161] <Person:0x6000002033a0> name:(null) age:0
2023-02-26 20:02:19.759661+0800 构造方法[29043:905161] <Person:0x600000203400> name:(null) age:0
2023-02-26 20:02:19.759684+0800 构造方法[29043:905161] <Person:0x600000203460> name:wuyujin1997 age:26
2023-02-26 20:02:19.759704+0800 构造方法[29043:905161] <Person:0x6000002033a0> name:测试赋值 age:22
Program ended with exit code: 0