动态获取对象属性

+ (BOOL)isContainsKey:(id)data {
    unsigned int numIvars;    Ivar *vars = class_copyIvarList([data class], &numIvars);    NSString *key = nil;    for (int i = 0; i < numIvars; i++) {
        Ivar thisIvar = vars[i];        key = [NSString stringWithUTF8String:ivar_getName(thisIvar)];        if ([key isEqualToString:@"_is_focus"]) {
            BOOL flag = [[data valueForKey:@"is_focus"] boolValue];            return flag;        }
    }
    free(vars);    return false;}

//可结合KVC获取属性值，避免无属性出错