在运行时检查ObjC属性是否可以为空

#import <objc/runtime.h>

// 定义一个类
@interface MyClass : NSObject

@property (nonatomic, nullable, strong) NSString *nullableString;
@property (nonatomic, strong) NSString *nonnullString;

@end

@implementation MyClass

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // 获取类的属性列表
        unsigned int count;
        objc_property_t *properties = class_copyPropertyList([MyClass class], &count);
        
        for (unsigned int i = 0; i < count; i++) {
            objc_property_t property = properties[i];
            
            // 获取属性的特性字符串
            const char *attributes = property_getAttributes(property);
            NSString *attributesString = [NSString stringWithUTF8String:attributes];
            
            // 检查特性字符串中是否包含nullable修饰符
            if ([attributesString containsString:@"nullable"]) {
                NSLog(@"%@ can be null", @(property_getName(property)));
            } else {
                NSLog(@"%@ cannot be null", @(property_getName(property)));
            }
        }
        
        free(properties);
    }
    return 0;
}

nullableString can be null
nonnullString cannot be null