Question

我是这个objective-c属性属性的新手。这是代码：

student.h

#import <Foundation/NSObject.h>
@interface Student: NSObject

@property int age(assign, readwrite); //I don't know what attribute it should have
@property NSString *name(retain, readwrite); //this one either

-(Student*) initWithName: (NSString *) n andAge:(int) a;
-(void) speakName;
+(void) smoke:(NSString*) thing;

@end

student.m

#import "student.h"

@implementation Student

-(Student*) initWithName:(NSString*) n andAge:(int) a {
    self = [super init];
    if(self) {
        [self setName: n];
        [self setAge: a];
    }
    return self;
}

-(void) speakName {
    NSLog(@"MyName is %@", _name);
}


+(void) smoke:(NSString*) thing {
    NSLog(@"Smoking %@", thing);
}
@end

的main.m

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

int main(void) {
    Student *student = [[Student alloc] initWithName: @"Markson" andAge: 29];
    [student speakName];
    [Student smoke:@"weed"];
    [student release];
    return 0;
}

为行

@property int age(assign, readwrite); //I don't know what attribute it should have
@property NSString *name(retain, readwrite); //this one either

当我不给他们任何东西时，编译器会给我4个警告：

In file included from student.m:1:
./student.h:5:1: warning: no 'assign', 'retain', or 'copy' attribute is
      specified - 'assign' is assumed [-Wobjc-property-no-attribute]
@property NSString *name;
^
./student.h:5:1: warning: default property attribute 'assign' not appropriate
      for non-GC object [-Wobjc-property-no-attribute]
2 warnings generated.
In file included from main.m:2:
./student.h:5:1: warning: no 'assign', 'retain', or 'copy' attribute is
      specified - 'assign' is assumed [-Wobjc-property-no-attribute]
@property NSString *name;
^
./student.h:5:1: warning: default property attribute 'assign' not appropriate
      for non-GC object [-Wobjc-property-no-attribute]
2 warnings generated.

请问任何人都可以知道年龄和名称属性应该使用哪些属性？

Answer 1

将这些行更改为：

@property (assign, nonatomic) int age;
@property (retain, nonatomic) NSString *name;

readwrite是默认设置，因此您无需进行设置。

查看此文档：

Encapsulating data in Objective-C

Answer 2

@property int age(assign, readwrite); //I don't know what attribute it should have
@property NSString *name(retain, readwrite); //this one either

简短说明：

如果要为int，float，BOOL等原始类型创建属性，请使用assign

如果您想保留该值，请使用strong或retain。

在所有其他情况下，您可以使用weak。

始终使用atomic，语法就像这样

@property (<assign/retain/weak>, <atomic/nonatomic>, <read/readwrite>) <dataType> <propertyName>;

无法为实例变量找到适当的属性属性

2 个答案: