(十七)[OC高效系列]为你的模型对象加上description方法

1.为什么要为你的模型对象加上description方法

比如类Person

@interface Person : NSObject
@property (nonatomic,copy) NSString *name;
@property (nonatomic,assign) int  age;
@property (nonatomic,strong) NSDate *birthday;
@end

@implementation Person
@end

我们平时将它的一个对象打印

Person *p = [[Person alloc] init];
p.name = @"aaa";
p.birthday = [NSDate date];
p.age = 18;
NSLog(@"%@",p);

然而打印的结果，却并不是我们想要的，我们更想要打印其中的各个属性的值

2016-08-16 11:38:27.860 Demo[30316:1805760] <Person: 0x7ff84b811ae0>

所以我们可以实现description方法

@implementation Person
-(NSString *)description{
    return [NSString stringWithFormat:@"name : %@ age : %d ,birthday : %@",self.name,self.age,self.birthday];
}
@end

这样打印的结果如下

2016-08-16 11:53:06.024 Demo[31045:1826418] 
name : aaa age : 18 ,birthday : 2016-08-16 03:53:06 +0000

看起来更加清晰了

2.使用NSDictionary来辅助实现description

也许description方法可以这样实现

@implementation Person
-(NSString *)description{
    NSMutableDictionary *properties  = [NSMutableDictionary dictionary];
    properties[@"name"] = self.name;
    properties[@"age"] = [NSNumber numberWithInt:self.age];
    properties[@"birthday"] = self.birthday;
    return [NSString stringWithFormat:@"%@",properties];
}
@end

这样打印出来就是这样

2016-08-16 11:59:14.195 Demo[31083:1830255] {
    age = 18;
    birthday = "2016-08-16 03:59:14 +0000";
    name = aaa;
}

打印的整洁，易看，而且还不用写那么多String的格式语句。

3.使用runtime辅助实现

虽然借助NSDictionary可以方便一点，但是当成员变量增多的时候仍然需要一个一个加入到字典中，比较麻烦。所以我们可以借助runtime自动遍历类中的所有属性

@implementation NSObject (YXParams)
- (NSDictionary *)keyValues
{
    NSMutableDictionary *props = [NSMutableDictionary dictionary];
    unsigned int outCount, i;
    objc_property_t *properties = class_copyPropertyList([self class], &outCount);
    
    NSDictionary *values;
    NSDictionary *propertyNames;
    if ([self respondsToSelector:@selector(paramsValueReplace)]) {
        values=[self paramsValueReplace];
    }
    if ([self respondsToSelector:@selector(paramsNamesReplace)]) {
        propertyNames=[self paramsNamesReplace];
    }
    for (i = 0; i<outCount; i++)
    {
        objc_property_t property = properties[i];
        const char* char_f =property_getName(property);
        NSString *propertyName = [NSString stringWithUTF8String:char_f];
        
        id propertyValue;
        if (values[propertyName]) {
            propertyValue=values[propertyName];
        }else{
            propertyValue= [self valueForKey:(NSString *)propertyName];
        }
        
        if (propertyNames[propertyName]) {
            propertyName=propertyNames[propertyName];
        }

        if (propertyValue) {
            [props setObject:propertyValue forKey:propertyName];
        }
    }
    free(properties);
    return props;
}
end

这样description方法就变为

@implementation Person
- (NSString *)description{
    return [NSString stringWithFormat:@"%@",[self keyValues]];
}
@end

这样是不是就很简单了?

4.防止无限递归

上面的方式虽然简单了，但是仍然会有问题，那就是当A有一个B的属性，B有一个A的属性的时候，调用A 或者 B的对象的打印，都会造成无限递归。比如:
Person:

@interface Person : NSObject
@property (nonatomic,copy) NSString *name;
@property (nonatomic,assign) int  age;
@property (nonatomic,strong) NSDate *birthday;
@property (nonatomic,weak) Tool *tool;
@end
@implementation Person
- (NSString *)description{
    return [NSString stringWithFormat:@"%@",[self keyValues]];
}
@end

Tool:

@interface Tool : NSObject
@property (nonatomic,copy) NSString *name;
@property (nonatomic,assign) float price;
@property (nonatomic,weak) Person *person;
@end
@implementation Tool
- (NSString *)description{
    return [NSString stringWithFormat:@"%@",[self keyValues]];
}
@end

调用场景

Person *p = [[Person alloc] init];
p.name = @"aaa";
p.birthday = [NSDate date];
p.age = 18;
Tool *tool = [[Tool alloc] init];
tool.name = @"锤子";
tool.price = 11;
tool.person = p;
p.tool = tool;
NSLog(@"%@",p);

这样就会出现如下的递归错误:

递归错误

怎么解决呢？

5.在使用runtime获取属性的时候，进行过滤

这样keyValues方法就要改成如下的形式，通过一个block进行过滤

- (NSDictionary *)keyValuesWithFilter:(BOOL(^)(NSString *propertyName,id value))filter
{
    NSMutableDictionary *props = [NSMutableDictionary dictionary];
    unsigned int outCount, i;
    objc_property_t *properties = class_copyPropertyList([self class], &outCount);
    
    NSDictionary *values;
    NSDictionary *propertyNames;
    if ([self respondsToSelector:@selector(paramsValueReplace)]) {
        values=[self paramsValueReplace];
    }
    if ([self respondsToSelector:@selector(paramsNamesReplace)]) {
        propertyNames=[self paramsNamesReplace];
    }
    for (i = 0; i<outCount; i++)
    {
        objc_property_t property = properties[i];
        const char* char_f =property_getName(property);
        NSString *propertyName = [NSString stringWithUTF8String:char_f];
        
        id propertyValue;
        if (values[propertyName]) {
            propertyValue=values[propertyName];
        }else{
            propertyValue= [self valueForKey:(NSString *)propertyName];
        }
        
        if (propertyNames[propertyName]) {
            propertyName=propertyNames[propertyName];
        }
        
        if (propertyValue) {
            //在此处利用block过滤一下
            if(filter(propertyName,propertyValue))
                [props setObject:propertyValue forKey:propertyName];
        }
    }
    free(properties);
    return props;
}

我们只需要把其中一个对象的description方法变成如下形式就好了,比如tool:

@implementation Tool
- (NSString *)description{
    return [NSString stringWithFormat:@"%@",[self keyValuesWithFilter:^BOOL(NSString *propertyName, id value) {
        if([value isKindOfClass:[Person class]]){
            Person *p = (Person *)value;
            if(p.tool == self){
                return NO;
            }
        }
        return YES;
    }]];
}
@end

这样打印就不会出现无线递归错误了。

6.使用xCodeGenerateDescriptionPlugin插件自动生成description方法

上面的方法，我们还可以使用插件自动为类生成description方法

Github地址