我正在尝试编写一个可以捕获Windows消息的类库，以便在已连接或删除设备时通知我。通常，在Windows窗体应用程序中，我只是覆盖WndProc方法，但在这种情况下没有WndProc方法。还有其他方法可以收到消息吗？
答案 0 :(得分：40)
你需要一个窗口，没有办法解决这个问题。这是一个示例实现。为DeviceChangeNotifier.DeviceNotify事件实现事件处理程序以获取通知。在程序开始时调用DeviceChangeNotifier.Start（）方法。在程序结束时调用DeviceChangeNotifier.Stop（）。请注意，DeviceNotify事件是在后台线程上引发的，请确保根据需要锁定以保持代码的线程安全。
using System;
using System.Windows.Forms;
using System.Threading;
class DeviceChangeNotifier : Form {
public delegate void DeviceNotifyDelegate(Message msg);
public static event DeviceNotifyDelegate DeviceNotify;
private static DeviceChangeNotifier mInstance;
public static void Start() {
Thread t = new Thread(runForm);
t.SetApartmentState(ApartmentState.STA);
t.IsBackground = true;
t.Start();
}
public static void Stop() {
if (mInstance == null) throw new InvalidOperationException("Notifier not started");
DeviceNotify = null;
mInstance.Invoke(new MethodInvoker(mInstance.endForm));
}
private static void runForm() {
Application.Run(new DeviceChangeNotifier());
}
private void endForm() {
this.Close();
}
protected override void SetVisibleCore(bool value) {
// Prevent window getting visible
if (mInstance == null) CreateHandle();
mInstance = this;
value = false;
base.SetVisibleCore(value);
}
protected override void WndProc(ref Message m) {
// Trap WM_DEVICECHANGE
if (m.Msg == 0x219) {
DeviceNotifyDelegate handler = DeviceNotify;
if (handler != null) handler(m);
}
base.WndProc(ref m);
}
}
答案 1 :(得分：5)
我有一个工作的USB通信类，如果有人感兴趣的话，会以稍微不同的方式实现设备更改通知。它非常紧凑（没有评论），并且不依赖于客户端中的Threading或OnSourceInitialized和HwndHandler内容。此外，您不需要提到的Form或Window。可以使用您可以覆盖WndProc()的任何类型。我使用Control。
该示例仅包含通知所需的代码，而不包含任何其他内容。示例代码是C ++ / CLI，虽然我没有订阅将可执行代码放在头文件中的做法，但为了简洁起见，我在这里这样做。
#pragma once
#include <Windows.h> // Declares required datatypes.
#include <Dbt.h> // Required for WM_DEVICECHANGE messages.
#include <initguid.h> // Required for DEFINE_GUID definition (see below).
namespace USBComms
{
using namespace System;
using namespace System::Runtime::InteropServices;
using namespace System::Windows;
using namespace System::Windows::Forms;
// This function is required for receieving WM_DEVICECHANGE messages.
// Note: name is remapped "RegisterDeviceNotificationUM"
[DllImport("user32.dll" , CharSet = CharSet::Unicode, EntryPoint="RegisterDeviceNotification")]
extern "C" HDEVNOTIFY WINAPI RegisterDeviceNotificationUM(
HANDLE hRecipient,
LPVOID NotificationFilter,
DWORD Flags);
// Generic guid for usb devices (see e.g. http://msdn.microsoft.com/en-us/library/windows/hardware/ff545972%28v=vs.85%29.aspx).
// Note: GUIDs are device and OS specific and may require modification. Using the wrong guid will cause notification to fail.
// You may have to tinker with your device to find the appropriate GUID. "hid.dll" has a function `HidD_GetHidGuid' that returns
// "the device interfaceGUID for HIDClass devices" (see http://msdn.microsoft.com/en-us/library/windows/hardware/ff538924%28v=vs.85%29.aspx).
// However, testing revealed it does not always return a useful value. The GUID_DEVINTERFACE_USB_DEVICE value, defined as
// {A5DCBF10-6530-11D2-901F-00C04FB951ED}, has worked with cell phones, thumb drives, etc. For more info, see e.g.
// http://msdn.microsoft.com/en-us/library/windows/hardware/ff553426%28v=vs.85%29.aspx.
DEFINE_GUID(GUID_DEVINTERFACE_USB_DEVICE, 0xA5DCBF10L, 0x6530, 0x11D2, 0x90, 0x1F, 0x00, 0xC0, 0x4F, 0xB9, 0x51, 0xED);
/// <summary>
/// Declare a delegate for the notification event handler.
/// </summary>
/// <param name="sender">The object where the event handler is attached.</param>
/// <param name="e">The event data.</param>
public delegate void NotificationEventHandler(Object^ sender, EventArgs^ e);
/// <summary>
/// Class that generetaes USB Device Change notification events.
/// </summary>
/// <remarks>
/// A Form is not necessary. Any type wherein you can override WndProc() can be used.
/// </remarks>
public ref class EventNotifier : public Control
{
private:
/// <summary>
/// Raises the NotificationEvent.
/// </summary>
/// <param name="e">The event data.</param>
void RaiseNotificationEvent(EventArgs^ e) {
NotificationEvent(this, e);
}
protected:
/// <summary>
/// Overrides the base class WndProc method.
/// </summary>
/// <param name="message">The Windows Message to process. </param>
/// <remarks>
/// This method receives Windows Messages (WM_xxxxxxxxxx) and
/// raises our NotificationEvent as appropriate. Here you should
/// add any message filtering (e.g. for the WM_DEVICECHANGE) and
/// preprocessing before raising the event (or not).
/// </remarks>
virtual void WndProc(Message% message) override {
if(message.Msg == WM_DEVICECHANGE)
{
RaiseNotificationEvent(EventArgs::Empty);
}
__super::WndProc(message);
}
public:
/// <summary>
/// Creates a new instance of the EventNotifier class.
/// </summary>
EventNotifier(void) {
RequestNotifications(this->Handle); // Register ourselves as the Windows Message processor.
}
/// <summary>
/// Registers an object, identified by the handle, for
/// Windows WM_DEVICECHANGE messages.
/// </summary>
/// <param name="handle">The object's handle.</param>
bool RequestNotifications(IntPtr handle) {
DEV_BROADCAST_DEVICEINTERFACE NotificationFilter;
ZeroMemory(&NotificationFilter, sizeof(NotificationFilter));
NotificationFilter.dbcc_devicetype = DBT_DEVTYP_DEVICEINTERFACE;
NotificationFilter.dbcc_size = sizeof(DEV_BROADCAST_DEVICEINTERFACE);
NotificationFilter.dbcc_reserved = 0;
NotificationFilter.dbcc_classguid = GUID_DEVINTERFACE_USB_DEVICE;
return RegisterDeviceNotificationUM((HANDLE)handle, &NotificationFilter, DEVICE_NOTIFY_WINDOW_HANDLE) != NULL;
}
/// <summary>
/// Defines the notification event.
/// </summary>
virtual event NotificationEventHandler^ NotificationEvent;
};
}
然后，在“接收者”（订阅和使用我们的NotificationEvent的对象）中，您所要做的就是：
void Receiver::SomeFunction(void)
{
USBComms::EventNotifier usb = gcnew USBComms::EventNotifier();
usb->NotificationEvent += gcnew USBComms::NotificationEventHandler(this, &Receiver::USBEvent);
}
void Receiver::USBEvent(Object^ sender, EventArgs^ e)
{
// Handle the event notification as appropriate.
}
答案 2 :(得分：1)
在Windows CE / Windows Mobile / SmartDevice项目中，标准Form不提供对WndProc方法的覆盖，但这可以通过基于Microsoft.WindowsCE.Forms.MessageWindow创建类来实现。 ，创建一个采用表单的构造函数，将该表单保存在局部变量中，以便在检测到消息时可以调用该表单上的方法。这是一个按比例缩小的示例来说明。希望这对CE / Windows Mobile世界的某些人有所帮助。
public class MsgWindow : Microsoft.WindowsCE.Forms.MessageWindow {
public const int WM_SER = 0x500;
public const int WM_SER_SCANDONE = WM_SER + 0;
frmMain msgform { get; set; }
public MsgWindow(frmMain msgform) {
this.msgform = msgform;
}
protected override void WndProc(ref Microsoft.WindowsCE.Forms.Message m) {
switch (m.Msg) {
case WM_SER_SCANDONE:
this.msgform.RespondToMessage(WM_SER_SCANDONE);
break;
default:
break;
}
base.WndProc(ref m);
}
}
public partial class frmMain : Form {
public frmMain() {
InitializeComponent();
}
public void RespondToMessage(int nMsg) {
try {
switch (nMsg) {
case MsgWindow.WM_SER_SCANDONE:
// do something here based on the message
break;
default:
break;
}
} catch (Exception ex) {
MessageBox.Show(string.Format("{0} - {1}", ex.Message, ex.ToString()), "RespondToMessage() Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation, MessageBoxDefaultButton.Button1);
// throw;
}
}
}