CODEWITHSUNDEEP
winapimessagevclc++builder-10.4-sydney
Max Kielland
Max Kielland

Reputation: 5841

Where are the rest of the TMessage missing params?

The VCL TMessage class provides the Message, WParam and LParam members, but a window message has more members:

typedef struct tagMSG {
  HWND   hwnd;
  UINT   message;
  WPARAM wParam;
  LPARAM lParam;
  DWORD  time;
  POINT  pt;
  DWORD  lPrivate;
} MSG, *PMSG, *NPMSG, *LPMSG;

Where are the hwnd, time, pt and lPrivate members? I'm in specially need of the time parameter.

Is there a way to access the original message that TMessage is constructed from (or any other means to get the time parameter)?

I'm handling my messages in TComponent::WndProc(Winapi::Messages::TMessage &Message).

Upvotes: 1

Views: 232

Answers (1)

Remy Lebeau
Remy Lebeau

Reputation: 597860

Where are the hwnd, time, pt and lPrivate members?

There aren't any such members in TMessage.

MSG is the structure that the Win32 API uses in a message loop to retrieve messages from a message queue, via the GetMessage() and PeekMessage() functions, prior to dispatching them to window procedures via DispatchMessage(). The time, pt, and lPrivate values are not delivered to a window procedure, however a window procedure can retrieve the time and pt values via the GetMessageTime() and GetMessagePos() functions, respectively (the lPrivate value is not accessible).

TMessage is the structure that the VCL uses in window procedures that are created by the RTL's MakeObjectInstance() function. This function allows classes, like the VCL's TWinControl and TTimer, to use non-static virtual WndProc() methods as Win32 window procedures.

In a standard Win32 window procedure, there are only 4 parameters available - hWnd, uMsg, wParam and lParam. An RTL-based window procedure ignores the hWnd (as it already knows exactly which object method to call), copies the uMsg, wParam and lParam values into a TMessage, calls the target WndProc() method passing it the TMessage, and then returns the TMessage::Result value back to the OS.

I'm in specially need of the time parameter. Is there a way to access the original message that TMessage is constructed from (or any other means to get the time parameter)?

If the message comes from the message queue of the thread that is calling your WndProc(), you can use the Win32 API GetMessageTime() function. Or, you can use the Win32 API SetWindowsHookEx() function to install a WH_GETMESSAGE hook into the thread's message queue.

If your component's WndProc() is called in the main UI thread specifically, you can alternatively use the VCL's TApplication::OnMessage or TApplicationEvents::OnMessage events, which receive a copy of the original MSG structure. Your component can use a private TApplicationEvents object to hook the OnMessage event.

However, a window procedure can receive both queued messages and non-queued messages, so if the message does not come from the calling thread's message queue at all, then there is simply no time (or pt) value available to retrieve for it, as non-queued messages do not go through the MSG structure to begin with.

I'm handling my messages in TComponent::WndProc(Winapi::Messages::TMessage &Message).

TComponent does not have a WndProc() method. Perhaps you are thinking of TWinControl::WndProc() instead?

Upvotes: 3

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