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Get declared property for object

 2 years ago
source link: https://fann.im/blog/2012/11/26/get-declared-property-for-object-in-objective-c/
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Get declared property for object

Nov 26, 2012

获取对象的 property 属性列表:

objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)
objc_property_t *protocol_copyPropertyList(Protocol *proto, unsigned int *outCount)

sample, via Declared Properties:

#import <objc/runtime.h>

id LenderClass = objc_getClass("Lender");

unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList(LenderClass, &outCount);

for (i = 0; i < outCount; i++)
{
    objc_property_t property = properties[i];
    fprintf(stdout, "%s %s\n", property_getName(property), property_getAttributes(property));
}
free(properties);

拿到 property 列表就可以很方便做一些东西，比如 autodescribe，根据列表取值然后组装成对象 description。再比如配合 NSCoder 做 NSObject 的序列化：

- (id)initWithCoder:(NSCoder *)decoder
{
    self = [super init]
    if (self)
    {
        Class clazz = [self class];
        NSUInteger count;

        objc_property_t *properties = class_copyPropertyList(clazz, &count);
        NSMutableArray *propertyArray = [NSMutableArray arrayWithCapacity:count];
        for (int i = 0; i < count ; i++)
        {
            objc_property_t property = properties[i];
            const char *propertyName = property_getName(property);
            [propertyArray addObject:[NSString stringWithCString:propertyName encoding:NSUTF8StringEncoding]];
        }
        free(properties);

        for (NSString *name in propertyArray)
        {
            id value = [decoder decodeObjectForKey:name];
            [self setValue:value forKey:name];
        }
    }
    return self;
}

- (void)encodeWithCoder:(NSCoder *)coder
{
    Class clazz = [self class];
    NSUInteger count;

    objc_property_t *properties = class_copyPropertyList(clazz, &count);
    NSMutableArray *propertyArray = [NSMutableArray arrayWithCapacity:count];
    for (int i = 0; i < count ; i++)
    {
        objc_property_t property = properties[i];
        const char *propertyName = property_getName(property);
        [propertyArray addObject:[NSString stringWithCString:propertyName encoding:NSUTF8StringEncoding]];
    }
    free(properties);

    for (NSString *name in propertyArray)
    {
        id value = [self valueForKey:name];
        [coder encodeObject:value forKey:name];
    }
}

也可以拿到成员变量列表: class_copyIvarList(Class cls, unsigned int *outCount). Objective-C Runtime 有很多东西可以学习的。

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