uniappx 混编 UsbDeviceConnection 定义为空，不行啊，搞了好久都不行，哪位大哥知道怎么弄

        const usbManager = context.getSystemService(Context.USB_SERVICE) as UsbManager;  

        const deviceListMap : HashMap<String, UsbDevice> = usbManager.getDeviceList();  

        let connection : UsbDeviceConnection = null;  
        let inEndpoint : UsbEndpoint = null; // usb 外接设备向平板输入  

        let bytes : ByteArray = new ByteArray(64);  
        deviceListMap.forEach((key : String, value : UsbDevice) => {  
            if (value.getProductId() == 23) {  
                connection = usbManager.openDevice(value);  
                const usbInterface : UsbInterface = value.getInterface(0);  
                connection.claimInterface(usbInterface, true);  
                inEndpoint = usbInterface.getEndpoint(0);  
            }  
        });  

        const count : Int = connection.bulkTransfer(inEndpoint, bytes, 64, 50);