unit UCallHwnd;

interface

uses
  Classes, Messages, Windows;

const
  WM_USER_MSG = WM_USER + 1;

type
  TCallHwnd = class(TObject)
  private
    FHwnd: THandle;
  protected
    procedure DoUserMessage(var AMsg: TMessage);
  public
    constructor Create;
    destructor Destroy; override;
    //调用测试
    function CallHwndTest: Boolean;
  end;

implementation

{ TCallHwnd }

function TCallHwnd.CallHwndTest: Boolean;
begin
  Result := PostMessage(FHwnd, WM_USER_MSG, 1, 2)
end;

constructor TCallHwnd.Create;
begin
  FHwnd := AllocateHWnd(DoUserMessage);
end;

destructor TCallHwnd.Destroy;
begin
  DeallocateHWnd(FHwnd);
  inherited;
end;

procedure TCallHwnd.DoUserMessage(var AMsg: TMessage);
begin
  if AMsg.Msg = WM_USER_MSG then
  begin
    //AMsg.LParam 2
    //AMsg.WParam 1
    //do something
  end
  else
    AMsg.Result := DefWindowProc(FHwnd, AMsg.Msg, AMsg.WPARAM, AMsg.LPARAM);
end;

end.