Capturing USB Plug/Unplug events in Firemonkey

Question

[RAD Studio XE3 / C++]
I have a FMX project running in Windows only at this stage, but I need to detect events when USB devices are connected and disconnected. I have a similar VCL app that can do this fine, but the Application->HookMainWindow is not exposed in FMX (only VCL).

Is there an elegant way to handle this? Or do I have to hack some VCL stuff into my FMX app to make that work? I'd imagine I have to abstract it so I can support other platforms down the track. For the meantime though I need to get the Windows solution working.

If the 'VCL hack' thing is required, how would I reference the vcl::Forms::Application from within my Fmx app?

Cheers.

Answer 1

This could help, using the TMessage way?

type
TMyMessageClass = class(TMessage)
MyProp1 : Integer;
MyProp2 : string;
end;

procedure MyForm.FormCreate(Sender: TObject);
begin
TMessageManager.DefaultManager.SubscribeToMessage(TMyMessageClass, Self.ProcessMessage);
end;

procedure MyForm.ProcessMessage(Sender : TObject; M : TMessage);
begin

if M is TMyMessageClass then
begin
//Do something
end;

end;

From the thread I do something like...

procedure TMyThread.Execute;
var
FMyMessage : TMyMessageClass;
begin

//stuff

Synchronize(
procedure
begin
FMyMessageClass := TMyMessageClass.Create;
FMyMessageClass.MyProp1 := 1;
FMyMessageClass.MyProp2 := 'Hello';
TMessageManager.DefaultManager.SendMessage(nil, FMyMessageClass);
end);

Hope this helps

Answer 2

I have found a solution, thanks to http://www.haogongju.net/art/1480814 It'd be nice to be able to attach some files but it looks like it's going to have to go inline.

SystemEvents.h

#ifndef SystemEventsH
#define SystemEventsH
#include <System.Classes.hpp>
#include <FMX.Controls.hpp>
#include <FMX.Forms.hpp>
#include "DeviceChanged.h"
//---------------------------------------------------------------------------
class TSystemEvents : TObject
{
private:
    TDeviceChangedMethod pDeviceChangeHandler;
    TForm *pOwnerForm;
#ifdef _Windows
    HWND Hwnd;      // Save the window handle
    LONG OldWndProc;// And remember the old WndProc so we can put it back later
#endif
public:
    __fastcall TSystemEvents(TForm *_pForm);
    __fastcall ~TSystemEvents();
    __property TForm *OwnerForm = {read=pOwnerForm};
#ifdef _Windows
    LRESULT __stdcall MessageHandler(Winapi::Messages::TMessage &Message);
#endif // _Windows
    __property TDeviceChangedMethod DeviceChangeHandler={read=pDeviceChangeHandler,write=pDeviceChangeHandler};
};
extern TSystemEvents *SystemEvents;
#endif

SystemEvents.cpp

#include <fmx.h>
#include <FMX.Platform.Win.hpp>
#pragma hdrstop
#include "SystemEvents.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#ifdef _Windows
LRESULT __stdcall WindowProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    if (SystemEvents == NULL)
    {
        return 0;
    }
    // This routine can't be a closure because the winapi needs to call it as
    // a LONGPTR.  So from here I can pass it into the SystemEvents object.
    Winapi::Messages::TMessage _Message;
    _Message.Msg = msg;
    _Message.WParam = wParam;
    _Message.LParam = lParam;
    return (LRESULT)SystemEvents->MessageHandler(_Message);
}
#endif //_Windows
__fastcall TSystemEvents::TSystemEvents(TForm *_pForm)
{
    pOwnerForm = _pForm;
    pDeviceChangeHandler = NULL;
#ifdef _Windows
    // Owner form handle is in FMX framework, but we want a Hwnd handle:
    Hwnd = FmxHandleToHWND(pOwnerForm->Handle);
    // Save the original WindowProc address
    OldWndProc = GetWindowLongPtr(Hwnd, GWL_WNDPROC);
    // Redirect the messages to my own function
    SetWindowLongPtr(Hwnd, GWL_WNDPROC, (LONG_PTR)&WindowProc);
#endif
}
__fastcall TSystemEvents::~TSystemEvents()
{
#ifdef _Windows
    // Very important we undo our hack before the app finishes
    SetWindowLongPtr(Hwnd, GWL_WNDPROC, OldWndProc);
#endif
}
LRESULT __stdcall TSystemEvents::MessageHandler(Winapi::Messages::TMessage &Message)
{
#ifdef _Windows
    if (Message.Msg == WM_DEVICECHANGE)
    {
        if (DeviceChangeHandler != NULL)
        {
            DeviceChangeHandler(this, new TDeviceChangedMessage(TDeviceChangedMessage::ParamForWin32wParam(Message.WParam)));
            return 1;
        }
    }
    return CallWindowProc((WNDPROC)OldWndProc, Hwnd, Message.Msg, Message.WParam, Message.LParam);
#endif
    return 0;
}

DeviceChanged.h

#ifndef DeviceChangedH
#define DeviceChangedH
//---------------------------------------------------------------------------
typedef enum {Unknown = 0, DeviceNodesChanged} DeviceChangedParam;
class TDeviceChangedMessage
{
private:
    DeviceChangedParam eParam;
public:
    TDeviceChangedMessage(DeviceChangedParam _eParam)
    {
        eParam = _eParam;
    }
    __property DeviceChangedParam Param={read=eParam};
    static DeviceChangedParam __fastcall ParamForWin32wParam(WPARAM _wParam);
};
typedef void __fastcall (__closure *TDeviceChangedMethod)(System::TObject* Sender, TDeviceChangedMessage* M);
#endif

DeviceChanged.cpp

#include <fmx.h>
#include <Dbt.h>
#pragma hdrstop
#include "DeviceChanged.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
DeviceChangedParam __fastcall TDeviceChangedMessage::ParamForWin32wParam(WPARAM _wParam)
{
    if (_wParam == DBT_DEVNODES_CHANGED)
        return DeviceChangedParam::DeviceNodesChanged;
    return DeviceChangedParam::Unknown;
}

To use it:

#include <SystemEvents.h>
TSystemEvents *SystemEvents;
// In Constructor:
{
    SystemEvents = new TSystemEvents(this);
    SystemEvents->DeviceChangeHandler = OnDeviceChanged;
}
// In Destructor:
{
    deletenullify(SystemEvents);
}
// Handler:
void __fastcall TMainForm::OnDeviceChanged(System::TObject* Sender, TDeviceChangedMessage *M)
{
    if (M->Param == DeviceChangedParam::DeviceNodesChanged)
    {
        OnUSBDeviceChanged();
    }
}

Works for me. :)