We use libusbx 1.0.16 in a Cocoa application in order to sync one or more
devices with a computer. Before upgrading from an earlier version of libusb we
had a hotplug listener built with IOKit, and then checked with libusb for the
new device.
Now we would like to trash the IOKit + libusb solution and go with just libusb,
since libusbx 1.0.16 comes with hotplug support.
I have followed the example for setting up device hotplug support, found
[here](http://libusbx.sourceforge.net/api-1.0/hotplug.html), and this is what
my callback currently looks like:
```c
int hotplug_callback(struct libusb_context *ctx, struct libusb_device *dev,
libusb_hotplug_event event, void *user_data) {
static libusb_device_handle *handle = NULL;
int rc;
struct libusb_device_descriptor desc;
(void)libusb_get_device_descriptor(dev, &desc);
if (LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED == event) {
printf("Got a device\n");
rc = libusb_open(dev, &handle);
if (LIBUSB_SUCCESS != rc) {
printf("Could not open USB device\n");
}
}
else if (LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT == event) {
printf("Lost a device\n");
if (handle) {
libusb_close(handle);
handle = NULL;
}
}
return 0;
}
```
When my application has finished launching (`-applicationDidFinishLaunching:`)
I run this snippet to setup a device hotplug listener:
```c
int rc;
rc = libusb_hotplug_register_callback(NULL, LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED
| LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT, LIBUSB_HOTPLUG_ENUMERATE, kVendorId,
kProductId, LIBUSB_HOTPLUG_MATCH_ANY, hotplug_callback, NULL, NULL);
if (LIBUSB_SUCCESS != rc) {
printf("Error creating a hotplug callback\n");
}
```
The results is not what I expect. When the application starts with a device
connected the log outputs `Got a device`. _But the callback is never called
when the device is unmounted or remounted, or when a device is mounted for the
first time after the application has finished loading._
**What I expect**
1. The callback is called on startup if a device is attached
2. The callback is called when a device is detached
3. The callback is called when a device is attached while the application is
running
Is there something wrong I'm doing in my code? I've read the documentation but
as far as I can see I'm using the function correctly. And
`libusb_has_capability(LIBUSB_CAP_HAS_HOTPLUG)` returns `1`.
---
Reply to this email directly or view it on GitHub:
https://github.com/libusbx/libusbx/issues/138
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