objective-c - objective-c /c : Detect USB drive via IOKit only on Mac

Question

这是我的代码，它会在我第一次运行应用程序时检测到设备，但在运行后它不会检测到新设备。

//Just for testing
 - (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
   [self detectUSB];
}

void detectUSB()
{
  //dictionary
  CFMutableDictionaryRef matchingDict = matchingDict = IOServiceMatching(kIOUSBDeviceClassName);

  //create notification
  IONotificationPortRef notificationObject; //notification object to listen
  mach_port_t masterPort = 0; //received from IOMasterPort
  notificationObject = IONotificationPortCreate(masterPort);

  //create run loop
  CFRunLoopSourceRef notificationRunLoopSource;

  //use notification obejct received from notificationPortCreate
  notificationRunLoopSource = IONotificationPortGetRunLoopSource(notificationObject);

  CFRunLoopAddSource(CFRunLoopGetCurrent(), notificationRunLoopSource, kCFRunLoopDefaultMode);

  IOServiceAddMatchingNotification(notificationObject,kIOFirstMatchNotification, matchingDict,isAttached,(__bridge void*)self,&iter );

  isAttached(NULL, iter);
}

void isAttached(void *refcon, io_iterator_t iterator) {

    io_service_t usbDevice;
    while((usbDevice = IOIteratorNext(iterator))) {
         io_name_t name; 
         IORegistryEntryGetName(usbDevice, name);
         printf("\tName:\t\t%s\n", (char *)name);

         CFNumberRef idProduct = (CFNumberRef)IORegistryEntrySearchCFProperty(usbDevice, kIOServicePlane, CFSTR("idProduct"), kCFAllocatorDefault, 0);
         uint16_t PID;
         CFNumberGetValue(idProduct, kCFNumberSInt16Type, (void *)&PID);
         printf("\tidProduct:\t0x%x\n", PID);

         IOObjectRelease(usbDevice);
         CFRelease(idProduct);
      }
   IOObjectRelease(iterator);
 }

此外，如果我拔下其中一个 USB 驱动器，我应该如何检测它？要不要再加一个

  IOServiceAddMatchingNotification(notificationObject,kIOFirstMatchNotification, matchingDict,isDetached,(__bridge void*)self,&iter );

在 isAttached 函数之后？实际上我添加了但它给了我错误的访问错误。你们能告诉我如何处理这些问题吗？谢谢!!

Answer 1

问题在于您的处理程序函数中的 IOObjectRelease() 调用。只要您想接收这些通知，就需要保留从 IOServiceAddMatchingNotification 获得的迭代器。如果您删除发布调用，代码将正常工作。

关于您的第二个问题:调用给出了错误的访问错误，因为 matchingDict 被 IOServiceAddMatchingNotification 释放。如果您在该调用之前执行了 CFRetain(matchingDict)，则可以使用相同的匹配字典添加第二个 Notification。 (顺便说一句:如果您对设备移除通知感兴趣，您应该传递 kIOTerminatedNotification 而不是 kIOFirstMatchNotification。