如何在Object-C中获取对象属性列表?

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我如何获得Objective-C中给定对象属性的列表(以NSArrayor 的形式NSDictionary)?

想象一下以下场景:我已经定义了刚刚延伸的父类NSObject,保存的NSString,一个BOOLNSData对象属性。然后我有几个类扩展了这个父类,每个类都增加了很多不同的属性。

有什么办法可以在通过整个对象的类上实现一个实例方法,并且返回NSArray每个(子类)类属性,NSStrings因为它们不在父类中,因此我可以稍后使用这些方法NSString对于KVC?

提问于
用户回答回答于

我只是自己找到了答案。通过使用Obj-C运行时库,我可以以我想要的方式访问这些属性:

- (void)myMethod {
    unsigned int outCount, i;
    objc_property_t *properties = class_copyPropertyList([self class], &outCount);
    for(i = 0; i < outCount; i++) {
        objc_property_t property = properties[i];
        const char *propName = property_getName(property);
        if(propName) {
            const char *propType = getPropertyType(property);
            NSString *propertyName = [NSString stringWithCString:propName
                                                                encoding:[NSString defaultCStringEncoding]];
            NSString *propertyType = [NSString stringWithCString:propType
                                                                encoding:[NSString defaultCStringEncoding]];
            ...
        }
    }
    free(properties);
}

这要求我创建一个‘getPropertyType’C函数,它主要取自一个Apple代码示例(现在不记得确切的源代码):

static const char *getPropertyType(objc_property_t property) {
    const char *attributes = property_getAttributes(property);
    char buffer[1 + strlen(attributes)];
    strcpy(buffer, attributes);
    char *state = buffer, *attribute;
    while ((attribute = strsep(&state, ",")) != NULL) {
        if (attribute[0] == 'T') {
            if (strlen(attribute) <= 4) {
                break;
            }
            return (const char *)[[NSData dataWithBytes:(attribute + 3) length:strlen(attribute) - 4] bytes];
        }
    }
    return "@";
}
用户回答回答于

// PropertyUtil.h
#import 

@interface PropertyUtil : NSObject

+ (NSDictionary *)classPropsFor:(Class)klass;

@end


// PropertyUtil.m
#import "PropertyUtil.h"
#import "objc/runtime.h"

@implementation PropertyUtil

static const char * getPropertyType(objc_property_t property) {
    const char *attributes = property_getAttributes(property);
    printf("attributes=%s\n", attributes);
    char buffer[1 + strlen(attributes)];
    strcpy(buffer, attributes);
    char *state = buffer, *attribute;
    while ((attribute = strsep(&state, ",")) != NULL) {
        if (attribute[0] == 'T' && attribute[1] != '@') {
            // it's a C primitive type:
            /* 
                if you want a list of what will be returned for these primitives, search online for
                "objective-c" "Property Attribute Description Examples"
                apple docs list plenty of examples of what you get for int "i", long "l", unsigned "I", struct, etc.            
            */
            return (const char *)[[NSData dataWithBytes:(attribute + 1) length:strlen(attribute) - 1] bytes];
        }        
        else if (attribute[0] == 'T' && attribute[1] == '@' && strlen(attribute) == 2) {
            // it's an ObjC id type:
            return "id";
        }
        else if (attribute[0] == 'T' && attribute[1] == '@') {
            // it's another ObjC object type:
            return (const char *)[[NSData dataWithBytes:(attribute + 3) length:strlen(attribute) - 4] bytes];
        }
    }
    return "";
}


+ (NSDictionary *)classPropsFor:(Class)klass
{    
    if (klass == NULL) {
        return nil;
    }

    NSMutableDictionary *results = [[[NSMutableDictionary alloc] init] autorelease];

    unsigned int outCount, i;
    objc_property_t *properties = class_copyPropertyList(klass, &outCount);
    for (i = 0; i < outCount; i++) {
        objc_property_t property = properties[i];
        const char *propName = property_getName(property);
        if(propName) {
            const char *propType = getPropertyType(property);
            NSString *propertyName = [NSString stringWithUTF8String:propName];
            NSString *propertyType = [NSString stringWithUTF8String:propType];
            [results setObject:propertyType forKey:propertyName];
        }
    }
    free(properties);

    // returning a copy here to make sure the dictionary is immutable
    return [NSDictionary dictionaryWithDictionary:results];
}




@end

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