Question

我是Objective-C的初学者，所以我尝试从这篇文章中完成Apple练习：Apple Objective-C guide

我尝试使用自定义getter和setter创建类属性，一个具有“weak”属性，另一个具有“copy”属性：

@property (weak, getter=getFirstName, setter=setFirstName:) NSString *firstName;
@property (copy, getter=getFirstName, setter=setFirstName:) NSString *secondName;

然后，我测试这样的属性：

NSString *name = @"John";
NSMutableString *surname = [NSMutableString stringWithString:@"Doe"];
MyPerson *person = [MyPerson createWithFirstName:name secondName:surname];
[person tellName];

name = nil;
[person tellName];
[NSThread sleepForTimeInterval:1.0f];
[surname appendString:@"dze"];
[person tellName];

所以我希望在名字设定为零后，弱财产也变成零;标记为“copy”的属性将处理它们自己的初始字符串副本，并将一些值附加到初始字符串不会对MyPerson对象造成任何后果。但是，当我调用log方法时，我在firstName中有原始值并在secondName中更改了值，就像没有“weak”和“copy”属性一样。

这是我记录的日志：

名字：约翰;第二个名字：Doe; BirthDate :( null）

名字：约翰;第二个名字：Doe; BirthDate :( null）

名字：约翰;第二个名字：Doedze; BirthDate :( null）

我期待这样的事情：

名字：约翰;第二个名字：Doe; BirthDate :( null）

名字：未指定;第二个名字：Doe; BirthDate :( null）

名字：未指定;第二个名字：Doe; BirthDate :( null）

据我所知，在第二行GC不能破坏firstName的值，但是第三次调用log方法在1秒睡眠后执行。我认为1秒足以让GC收集未使用的字符串。

任何idead为什么可以忽略“弱”和“复制”属性？谢谢你的帮助。

完整代码：的main.m：

#import <Foundation/Foundation.h>
#import "MyPerson.h"

int main(int argc, const char * argv[]) 
{
  @autoreleasepool
  {
     NSString *name = @"John";
     NSMutableString *surname = [NSMutableString stringWithString:@"Doe"];
     MyPerson *person = [MyPerson createWithFirstName:name secondName:surname];
     [person tellName];

     name = nil;
     [person tellName];
     [NSThread sleepForTimeInterval:1.0f];
     [surname appendString:@"dze"];
     [person tellName];
  }
  return 0;
}

MyPerson.h：

#import <Foundation/Foundation.h>

@interface MyPerson : NSObject

@property (weak, getter=getFirstName, setter=setFirstName:) NSString *firstName;
@property (copy, getter=getSecondName, setter=setSecondName:) NSString *secondName;
@property (getter=getBirthDate, setter=setBirthDate:) NSDate *birthDate;

-(void)setFirstName:(NSString *)firstName;
-(NSString *)getFirstName;

-(void)setSecondName:(NSString *)secondName;
-(NSString *)getSecondName;

-(void)setBirthDate:(NSDate *)birthDate;
-(NSDate *)getBirthDate;

-(void) tellName;

+(id)create;
+(id)createWithFirstName:(NSString *)firstName;
+(id)createWithFirstName:(NSString *)firstName secondName:(NSString *)secondName;
+(id)createWithFirstName:(NSString *)firstName secondName:(NSString *)secondName birthDate:(NSDate *)birthDate;

-(id)initWithFirstName:(NSString *)firstName secondName:(NSString *)secondName birthDate:(NSDate *)birthDate;

@end

MyPerson.m：

#import "MyPerson.h"

@implementation MyPerson

@synthesize firstName = m_firstName;
@synthesize secondName = m_secondName;
@synthesize birthDate = m_birthDate;

-(void)tellName
{
  NSMutableString *stringBuilder = [NSMutableString string];
  [stringBuilder appendString:@"First name: "];
  [self appendIfNotNil:self.firstName toBuilder:stringBuilder];
  [stringBuilder appendString:@"; "];
  [stringBuilder appendString:@"Second name: "];
  [self appendIfNotNil:self.secondName toBuilder:stringBuilder];
  [stringBuilder appendString:@"; "];
  [stringBuilder appendString:@"BirthDate: "];
  [stringBuilder appendFormat:@"%@", [m_birthDate     descriptionWithLocale:NSLocaleLanguageDirectionUnknown]];

  NSLog(@"%@", stringBuilder);
}

-(void)appendIfNotNil:(NSString*)str toBuilder:(NSMutableString *)stringBuilder
{
  [stringBuilder appendString:str == nil ? @"Not specified" : str];
}

-(void)setFirstName:(NSString *)firstName
{
  NSLog(@"Setter called for first name: %@", firstName);
  m_firstName = firstName;
}

-(NSString *)getFirstName
{
  NSLog(@"Getter called for first name");
  return m_firstName;
}

-(void)setSecondName:(NSString *)secondName
{
  NSLog(@"Setter called for second name: %@", secondName);
  m_secondName = secondName;
}

-(NSString *)getSecondName
{
  NSLog(@"Getter called for second name");
  return m_secondName;
}

-(id)initWithFirstName:(NSString *)firstName secondName:(NSString *)secondName birthDate:(NSDate *)birthDate
{
  self = [super init];
  if (self)
  {
    m_firstName = firstName;
    m_secondName = secondName;
    m_birthDate = birthDate;
  }

  return self;
}

+(id)createWithFirstName:(NSString *)firstName secondName:(NSString *)secondName birthDate:(NSDate *)birthDate
{
  MyPerson *person = [MyPerson alloc];
  person = [person initWithFirstName:firstName secondName:secondName birthDate:birthDate];
  return person;
}

+(id)createWithFirstName:(NSString *)firstName secondName:(NSString *)secondName
{
  return [MyPerson createWithFirstName:firstName secondName:secondName birthDate:nil];
}

+(id)createWithFirstName:(NSString *)firstName
{
  return [MyPerson createWithFirstName:firstName secondName:nil birthDate:nil];
}

+(id)create
{
   return [MyPerson createWithFirstName:nil secondName:nil birthDate:nil];
}


@end

为什么“弱”和“复制”属性可以被忽略？

Answer 1

任何想法，为什么＆＃34;弱＆＃34;和＆＃34;复制＆＃34;属性可以忽略吗？谢谢你的帮助。

他们不被忽视。你的测试存在缺陷。

要测试＆＃34; weak＆＃34;，您需要使用NSString以外的其他内容，因为字符串具有特殊的内存管理。使用没有变量引用的NSObject;它会在一阵烟雾中消失。
```
self.ob = [NSObject new];
NSLog(@"%@", self.ob); // nil!
```
要测试＆＃34; copy＆＃34;，您需要从NSMutableString开始，保持对它的引用，将其分配给属性，然后改变可变字符串;分配的字符串不会改变，证明该属性没有持有对同一可变字符串的另一个引用。
要测试内存管理属性（如copy）以及线程属性（如atomic），请不编写自己的setter！这些是编译器关于 it 应该如何编写setter（合成）的指令。如果您手动编写setter，则无法获得综合，此时您的属性毫无意义（除非他们告知客户您的API）。

＆＃34;弱＆＃34;和＆＃34;复制＆＃34;具有完全自定义getter和setter的属性的属性

1 个答案: