python ctypes 中的回调

Question

我正在尝试使用 ctypes 在 Python 中包装 C 库。函数调用需要一个回调函数，我使用编程手册实现了该函数。问题是我无法从该包装器中获取“True”返回值，而且我是回调函数的新手。

from ctypes import *

class USB2ish(object):
    def __init__(self):
        try:
            usbio_dll = cdll.LoadLibrary("C:\\Users\\...\\usb2uis.dll")
        except:
            print("dll file not loaded, 'USB-TO-UIS driver was not present/installed'.")

    def exception_handler(self, exception):
        print("Exception occured:", exception)


    def USBIO_OpenDevice(self):
        try:
            result = cdll.usb2uis.USBIO_OpenDevice()
            print('USBIO device Successfully opened with number', result)
            return result
        except Exception as ex:
            self.exception_handler(self, ex)

    def USBIO_SetTrigNotify(self, dev_no, result):
        """ The trigger event of USB2UIS device, pTrig_CallBack will be called.
        """

        # Define the callback function type
        USB_DLL_CALLBACK = CFUNCTYPE(c_bool, POINTER(Set_trigg))

        cl_back = USB_DLL_CALLBACK(self.process)
        set_trig = Set_trigg(dev_no, 170)   # "0x00AA" = 170
        print(set_trig)

    def process(self, dev_no, result):
        print(dev_no.contents.dev_index)
        print(result.contents.type)

if __name__ == "__main__":
    rs = USB2ish()
    result = rs.USBIO_OpenDevice()
    call_back = rs.USBIO_SetTrigNotify(0, result)

编程手册

如何在ctypes中使用回调方法？

Answer 1

三个问题：

首先声明：

USB_DLL_CALLBACK = CFUNCTYPE(c_bool, POINTER(Set_trigg))

根据编程手册，回调的签名必须是

bool function(BYTE, DWORD)

。

其次，我没有看到你在DLL中调用

USBIO_SetTrigNotify

的位置。

第三，您将

dev_no

和

result

作为参数传递给方法

USBIO_SetTrigNotify

，但这些将是 USBIO 将传递给您的回调的参数。

将所有内容放在一起（未经测试，因为我没有 DLL）：

from ctypes import wintypes
from ctypes import *

class USB2ish(object):
    def __init__(self):
        try:
            usbio_dll = cdll.LoadLibrary("C:\\Users\\...\\usb2uis.dll")
        except:
            print("dll file not loaded, 'USB-TO-UIS driver was not present/installed'.")

    def exception_handler(self, exception):
        print("Exception occured:", exception)


    def USBIO_OpenDevice(self):
        try:
            result = cdll.usb2uis.USBIO_OpenDevice()
            print('USBIO device Successfully opened with number', result)
            return result
        except Exception as ex:
            self.exception_handler(self, ex)

    def USBIO_SetTrigNotify(self):
        callback = CFUNCTYPE(c_bool, BYTE, DWORD)(self.process)
        return cdll.usb2uis.USBIO_SetTrigNOtify(callback)

    def process(self, i_dev_index, i_type):
        print(f'{i_dev_index=}')
        print(f'{i_type=}')

if __name__ == "__main__":
    rs = USB2ish()
    result = rs.USBIO_OpenDevice()
    rs.USBIO_SetTrigNotify()