Making the app single-instanced

Single-instanced apps only allow one instance of the app running at a time. Flutter Windows apps are multi-instanced by default. If a first instance exists when trying to start a new instance, end the new instance and activate the first instance.

Via the FindWindow method

Find the window HWND named single_instance_example by FindWindow, activate the window if it exists and end the current program.

Please change single_instance_example to the name of your app.

Change the file windows/runner/main.cpp as follows:

// ...

int APIENTRY wWinMain(_In_ HINSTANCE instance, _In_opt_ HINSTANCE prev,
                      _In_ wchar_t *command_line, _In_ int show_command) {
  HWND hwnd = ::FindWindow(L"FLUTTER_RUNNER_WIN32_WINDOW", L"single_instance_example");
  if (hwnd != NULL) {
    ::ShowWindow(hwnd, SW_NORMAL);
    ::SetForegroundWindow(hwnd);
    return EXIT_FAILURE;
  }

  // ...

  if (!window.CreateAndShow(L"single_instance_example", origin, size)) {
    return EXIT_FAILURE;
  }

  // ...
}