第17条：实现description方法

覆写description方法

调试程序时，需要打印并查看对象信息，这时候可以借助description方法和debugDescription方法。其中debugDescription方法是用于调试用的。

覆写description方法并将描述对象的字符串返回即可。

如：
EOCPerson类

/* EOCPerson头文件 */
#import <Foundation/Foundation.h>

@interface EOCPerson : NSObject

@property(nonatomic ,copy, readonly) NSString *firstName;
@property(nonatomic ,copy, readonly) NSString *lastName;
- (id)initWithFirstName:(NSString *)firstName andLastName:(NSString *)lastName;
@end

/* EOCPerson实现文件 */
#import "EOCPerson.h"

@implementation EOCPerson
- (id)initWithFirstName:(NSString *)firstName andLastName:(NSString *)lastName{
    if (self = [super init]) {
        _firstName = [firstName copy];
        _lastName = [lastName copy];
    }
    return self;
}

// 覆写description方法
- (NSString *)description{
    return [NSString stringWithFormat:@"%@ %@", _firstName, _lastName];
}

// 覆写debugDescription方法，用于调试
- (NSString *)debugDescription{
    return [NSString stringWithFormat:@"<%@: %p, \"%@ %@\">", [self class], self, _firstName, _lastName];
}

EOCLocation类

/* EOCLocation头文件  */
#import <Foundation/Foundation.h>

@interface EOCLocation : NSObject

@property(nonatomic ,copy, readonly) NSString *title;
@property(nonatomic ,assign, readonly) float latitude;  // 纬度
@property(nonatomic ,assign, readonly) float longitude; // 经度
- (id)initWithTitle:(NSString *)title
           latitude:(float)latitude
          longitude:(float)longitude;
@end

/* EOCLocation实现文件  */
#import "EOCLocation.h"

@implementation EOCLocation

- (id)initWithTitle:(NSString *)title latitude:(float)latitude longitude:(float)longitude{
    if (self = [super init]) {
        _title = [title copy];
        _latitude = latitude;
        _longitude = longitude;
    }
    return self;
}

// 覆写description，且将属性信息包装到字典中
- (NSString *)description{
    return [NSString stringWithFormat:@"%@",
            @{@"title": _title,
              @"latitude": @(_latitude),
              @"longitude": @(_longitude)
              }
            ];
}

// 覆写debugDescription，且将属性信息包装到字典中，用于调试
- (NSString *)debugDescription{
    return [NSString stringWithFormat:@"<%@, %p, %@>",
            [self class],
            self,
            @{@"title": _title,
              @"latitude": @(_latitude),
              @"longitude": @(_longitude)
              }
            ];
}

@end

main函数

#import <Foundation/Foundation.h>
#import "EOCPerson.h"
#import "EOCLocation.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        EOCPerson *person = [[EOCPerson alloc] initWithFirstName:@"Bob" andLastName:@"Smith"];
        NSLog(@"person = %@", person);
        
        EOCLocation *location = [[EOCLocation alloc] initWithTitle:@"London" latitude:51.506 longitude:0];
        NSLog(@"location = %@", location);
        
    }
    return 0;
}

输出结果：

Snip20160318_29.png

要点

• 实现description方法返回一个有意义的字符串，用以描述该实例。
• 若想在调试时打印出更详尽的对象描述信息，则应实现debugDescription方法。