How to receive WM_POWERBROADCAST inside of a thread?

Question

I\'ve been beating my head for over a day now, going through tons of resources trying to figure out how to receive the WM_POWERBROADCAST Windows message from within

Answer 1

WM_POWERBROADCAST is not a posted message, so your message loop will never see it. You need a window procedure to receive that message. Your thread code is using DefWindowProc() directly as the window procedure. Change the call to RegisterClass() to register a custom procedure instead, that then calls DefWindowProc() for unhandled messages. GetMessage() will dispatch any sent message directly to the window procedure, and DispatchMessage() will dispatch any posted messages to the same window procedure.

unit JD.ThreadTest;

interface

uses
  System.Classes, Winapi.Messages, Winapi.Windows;

type
  TDataThread = class(TThread)
  private
    FTitle: String;
    FWnd: HWND;
    FWndClass: WNDCLASS;
    procedure HandleMessage(var Message: TMessage);
  protected
    procedure Execute; override;
    procedure DoTerminate; override;
  public
   constructor Create(const Title: String); reintroduce;
  end;

implementation

function DataThreadWndProc(Wnd: HWND; Msg: UINT; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall;
var
  Thread: TDataThread;
  Message: TMessage;
begin
  if Msg = WM_NCCREATE then
  begin
    Thread := TDataThread(PCREATESTRUCT(lParam)^.lpCreateParams);
    SetWindowLongPtr(Wnd, GWLP_USERDATA, LONG_PTR(Thread));
  end else
    Thread := TDataThread(GetWindowLongPtr(Wnd, GWLP_USERDATA));

  if Thread <> nil then
  begin
    Message.Msg := Msg;
    Message.WParam := wParam;
    Message.LParam := lParam;
    Message.Result := 0;
    Thread.HandleMessage(Message);
    Result := Message.Result;
  end else
    Result := DefWindowProc(Wnd, Msg, wParam, lParam);
end;

constructor TDataThread.Create(const Title: String);
begin
  inherited Create(True);
  FTitle := Title;
  with FWndClass do
  begin
    Style := 0;
    lpfnWndProc := @DataThreadWndProc;
    cbClsExtra := 0;
    cbWndExtra := 0;
    hInstance := HInstance;
    hIcon := 0;
    hCursor := LoadCursor(0, IDC_ARROW);
    hbrBackground := COLOR_WINDOW;
    lpszMenuName := nil;
    lpszClassName := 'TDataThread';
  end;
end;

procedure TDataThread.Execute;
var
  Msg: TMsg;
begin
  if Winapi.Windows.RegisterClass(FWndClass) = 0 then Exit;
  FWnd := CreateWindow(FWndClass.lpszClassName, PChar(FTitle), WS_OVERLAPPED, 0, 0, 0, 0, 0, 0, HInstance, Self);
  if FWnd = 0 then Exit;
  while GetMessage(Msg, 0, 0, 0) do
  begin
    if Terminated then Exit;
    TranslateMessage(msg);
    DispatchMessage(msg);
  end;
end;

procedure TDataThread.DoTerminate;
begin
  if FWnd <> 0 then DestroyWindow(FWnd);
  Winapi.Windows.UnregisterClass(FWndClass.lpszClassName, HInstance);
  inherited;
end;

procedure TDataThread.HandleMessage(var Message: TMessage);
begin
  case Message.Msg of
    WM_POWERBROADCAST:
    begin
      // ...
    end;
  else
    Message.Result := DefWindowProc(FWnd, Message.Msg, Message.WParam, Message.LParam);
  end;
end;

end.