I'm doing an asynchronous read from a USB printer. The read works correctly.
My trouble is updating a NSTextField from within the callback.
> -(IBAction)printTest:(id)sender
> { ….
> NSLog(@"starting async read: %@", _printerOutput);
> NSLog(@"_printerOutput pointer = %p", _printerOutput);
>
> result = (*interface)->ReadPipeAsyncTO(interface,
> 1,
> readBuffer,
> numBytesRead,
> 500,
> 1000,
>
> USBDeviceReadCompletionCallback,
> &(_printerOutput)
> );
The callback is defined as:
> void USBDeviceReadCompletionCallback(void *refCon, IOReturn result, void
> *messageArg)
> {
> NSTextField *printerOutput = (__bridge NSTextField *) messageArg;
> NSLog(@"_printerOutput pointer = %p", printerOutput);
> }
The pointer loses its value when inside of the callback.
2013-04-08 16:36:25.348 MyUSB[8120:303] starting async read: <NSTextField:
0x10221dc60>
2013-04-08 16:36:25.348 MyUSB[8120:303] _printerOutput pointer = 0x10221dc60
2013-04-08 16:36:27.166 MyUSB[8120:303] _printerOutput pointer = 0x0
I've looked in many places trying to mimic different ways to pass in the
pointer. There can be only one correct way. :)
Another variation on the theme: (__bridge void *)(_printerOutput). This
doesn't work, either.
I understand that the callback is of type IOAsyncCallback1.
Other URLs of note:
http://www.google.com/search?client=safari&rls=en&q=another+usb+notification+example&ie=UTF-8&oe=UTF-8
http://stackoverflow.com/questions/8010382/updating-ui-from-a-c-function-in-a-thread
Thank you for reading.
Caylan
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