Objective-C中NSLog打印Swift枚举触发EXC_BAD_ACCESS如何解决？

使用@objc标记桥接到Objective-C的Int类型Swift枚举，在OC侧属于值类型的NS_ENUM，本质是NSInteger基础数值类型，不是继承自NSObject的OC对象。
你之前的写法全部不符合类型规则：

• 用%@格式符打印时，%@会把传入的参数当做OC对象指针，向其发送description消息，你传入的枚举整数值会被识别为非法内存地址，直接触发EXC_BAD_ACCESS内存访问崩溃
• 尝试调用[operation description]、[operation value]会直接导致构建失败：基础数值类型不能接收OC消息，编译器会直接报语法错误

打印枚举值 #

快速打印原始数值 #

枚举本身是整数类型，直接用%ld格式符打印即可，注意要强转为long类型兼容64位系统：

NSLog(@"Completed with operation raw value: %ld", (long)operation);

打印可读的case名称 #

桥接到OC后，Swift枚举的case会自动加上枚举名作为前缀，你定义的几个case在OC侧的枚举值分别是OperationUnknown、OperationOperation1、OperationOperation2、OperationOperation1And2，可以通过switch匹配返回对应字符串：

NSString *operationStr = nil;
switch (operation) {
    case OperationUnknown:
        operationStr = @"Unknown";
        break;
    case OperationOperation1:
        operationStr = @"Operation1";
        break;
    case OperationOperation2:
        operationStr = @"Operation2";
        break;
    case OperationOperation1And2:
        operationStr = @"Operation1And2";
        break;
    default:
        operationStr = [NSString stringWithFormat:@"Undefined operation: %ld", (long)operation];
        break;
}
NSLog(@"Completed with operation: %@", operationStr);

布尔比较操作 #

枚举值是基础数值，直接用==做比较即可，不需要调用任何对象方法：

// 判断是否为Operation1
BOOL isFirstOperation = (operation == OperationOperation1);
if (isFirstOperation) {
    // 对应业务逻辑
}

// 判断是否为Operation1和Operation2的组合
BOOL isCombinedOperation = (operation == OperationOperation1And2);

如果后续需要频繁打印枚举值，可以直接在Swift侧给枚举扩展一个@objc的描述属性，桥接到OC后就可以直接调用拿到字符串，不用每次在OC侧写switch：

@objc extension Operation {
    var objcDescription: String {
        switch self {
        case .Unknown: return "Unknown"
        case .Operation1: return "Operation1"
        case .Operation2: return "Operation2"
        case .Operation1And2: return "Operation1And2"
        @unknown default: return "Invalid value: \(self.rawValue)"
        }
    }
}

桥接到OC后直接调用即可：

NSLog(@"Completed with operation: %@", [operation objcDescription]);

内容的提问来源于stack exchange，提问作者Dracula