WPF如何卸载U盘(弹出USB设备)

应用程序和硬件设备的通信过程是：应用程序使用CreateFile函数打开设备，然后用DeviceIoControl()与硬件设备通信.

CreateFile函数：

 [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    private static extern IntPtr CreateFile(
         string lpFileName,       
         uint dwDesiredAccess,
         uint dwShareMode,
         IntPtr SecurityAttributes,
         uint dwCreationDisposition,
         uint dwFlagsAndAttributes,
         IntPtr hTemplateFile);

DeviceIoControl函数：

 [DllImport("kernel32.dll", ExactSpelling = true, SetLastError = true, CharSet = CharSet.Auto)]
    private static extern bool DeviceIoControl(
        IntPtr hDevice, 
        uint dwIoControlCode,
        IntPtr lpInBuffer, 
        uint nInBufferSize,
        IntPtr lpOutBuffer, 
        uint nOutBufferSize,
        out uint lpBytesReturned, 
        IntPtr lpOverlapped
    );

const uint GENERIC_READ = 0x80000000;
const int GENERIC_WRITE = 0x40000000;
const int FILE_SHARE_READ = 0x1;
const int FILE_SHARE_WRITE = 0x2;
const int IOCTL_STORAGE_EJECT_MEDIA = 0x2D4808;

具体过程如下：

     1. 打开设备，得到设备的句柄handle.

IntPtr  handle = CreateFile(filename, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, IntPtr.Zero, 0x3, 0, IntPtr.Zero);

第一个参数filename与普通文件名有所不同，设备驱动的“文件名”(常称为“设备路径”)形式固定为“\.DeviceName”, 如 string filename = @"\.I:";

    2. 向目标设备发送设备控制码，也就是发送命令。IOCTL_STORAGE_EJECT_MEDIA  弹出U盘。

 uint byteReturned;
 DeviceIoControl(handle, IOCTL_STORAGE_EJECT_MEDIA, IntPtr.Zero, 0, IntPtr.Zero, 0, out byteReturned, IntPtr.Zero);