通过进程ID获取主窗句柄

function GetHwndFromProcess(const hPID: THandle): THandle;
  type
    PEnumInfo = ^TEnumInfo;
    TEnumInfo = record
    ProcessID: DWORD;
    HWND: THandle;
  end;

  function EnumWindowsProc(Wnd: DWORD; var EI: TEnumInfo): Bool; stdcall;
  var
  PID: DWORD;
  begin
    GetWindowThreadProcessID(Wnd, @PID);
    Result := (PID <> EI.ProcessID) or
        (not IsWindowVisible(WND)) or
        (not IsWindowEnabled(WND));

    if not Result then EI.HWND := WND;
  end;

  function FindMainWindow(PID: DWORD): DWORD;
  var
    EI: TEnumInfo;
  begin
    EI.ProcessID := PID;
    EI.HWND := 0;
    EnumWindows(@EnumWindowsProc, Integer(@EI));
    Result := EI.HWND;
  end;
begin
  if hPID <> 0 then
    Result := FindMainWindow(hPID)
  else
    Result:=0;
end;