[Feature-Request] Multi-Window Support

[CodeWithKamal]

Requesting the addition of multi-window support to the window_manager Flutter package.

Feature Request:

Enable the creation and management of multiple windows within a Flutter application. Each window should have independent widgets and state, enhancing the flexibility of Flutter apps.

Use Cases:

• Simultaneous multitasking.
• Custom UI layouts.
• Improved productivity for users.

Note:

Consideration for platform-specific behavior and minimal disruption to existing projects is essential. Feedback and suggestions are welcome.

[bingolead-stack]

So I finally found the solution for this. When working with multiple screen, you need to register plugin for each screen Just adding below code inside FlutterWindow::OnCreate() function in windows/Runner/flutter_window.cpp works for me!

#include <desktop_multi_window/desktop_multi_window_plugin.h>
#include <window_manager/window_manager_plugin.h>

  DesktopMultiWindowSetWindowCreatedCallback([](void *controller) {
    // get view controller and engine of new window
    auto *flutter_view_controller =
        reinterpret_cast<flutter::FlutterViewController *>(controller);
    auto *registry = flutter_view_controller->engine();

    WindowManagerPluginRegisterWithRegistrar(
        registry->GetRegistrarForPlugin("WindowManagerPlugin"));
  });

[chenguocan]

So I finally found the solution for this. When working with multiple screen, you need to register plugin for each screen Just adding below code inside FlutterWindow::OnCreate() function in windows/Runner/flutter_window.cpp works for me!

#include <desktop_multi_window/desktop_multi_window_plugin.h>
#include <window_manager/window_manager_plugin.h>

  DesktopMultiWindowSetWindowCreatedCallback([](void *controller) {
    // get view controller and engine of new window
    auto *flutter_view_controller =
        reinterpret_cast<flutter::FlutterViewController *>(controller);
    auto *registry = flutter_view_controller->engine();

    WindowManagerPluginRegisterWithRegistrar(
        registry->GetRegistrarForPlugin("WindowManagerPlugin"));
  });

This code, closing the window will cause the program to crash

[bingolead-stack]

Did you address issue? If not, you can reference from here

#include "flutter_window.h"

#include <optional>

#include <desktop_multi_window/desktop_multi_window_plugin.h>
#include <media_kit_libs_windows_video/media_kit_libs_windows_video_plugin_c_api.h>
#include <media_kit_video/media_kit_video_plugin_c_api.h>
#include <screen_brightness_windows/screen_brightness_windows_plugin.h>
#include <screen_retriever/screen_retriever_plugin.h>
#include <window_manager/window_manager_plugin.h>

#include "flutter/generated_plugin_registrant.h"

FlutterWindow::FlutterWindow(const flutter::DartProject &project)
    : project_(project) {}

FlutterWindow::~FlutterWindow() {}

bool FlutterWindow::OnCreate() {
  if (!Win32Window::OnCreate()) {
    return false;
  }

  RECT frame = GetClientArea();

  // The size here must match the window dimensions to avoid unnecessary surface
  // creation / destruction in the startup path.
  flutter_controller_ = std::make_unique<flutter::FlutterViewController>(
      frame.right - frame.left, frame.bottom - frame.top, project_);
  // Ensure that basic setup of the controller was successful.
  if (!flutter_controller_->engine() || !flutter_controller_->view()) {
    return false;
  }
  RegisterPlugins(flutter_controller_->engine());
  DesktopMultiWindowSetWindowCreatedCallback([](void *controller) {
    // get view controller and engine of new window
    auto *flutter_view_controller =
        reinterpret_cast<flutter::FlutterViewController *>(controller);
    auto *registry = flutter_view_controller->engine();

    MediaKitLibsWindowsVideoPluginCApiRegisterWithRegistrar(
        registry->GetRegistrarForPlugin("MediaKitLibsWindowsVideoPluginCApi"));
    MediaKitVideoPluginCApiRegisterWithRegistrar(
        registry->GetRegistrarForPlugin("MediaKitVideoPluginCApi"));
    ScreenBrightnessWindowsPluginRegisterWithRegistrar(
        registry->GetRegistrarForPlugin("ScreenBrightnessWindowsPlugin"));
    ScreenRetrieverPluginRegisterWithRegistrar(
        registry->GetRegistrarForPlugin("ScreenRetrieverPlugin"));
    WindowManagerPluginRegisterWithRegistrar(
        registry->GetRegistrarForPlugin("WindowManagerPlugin"));
  });

  SetChildContent(flutter_controller_->view()->GetNativeWindow());

  // flutter_controller_->engine()->SetNextFrameCallback([&]() {
  //   ""; // this->Show();
  // });

  // Flutter can complete the first frame before the "show window" callback is
  // registered. The following call ensures a frame is pending to ensure the
  // window is shown. It is a no-op if the first frame hasn't completed yet.
  // flutter_controller_->ForceRedraw();

  return true;
}

void FlutterWindow::OnDestroy() {
  if (flutter_controller_) {
    flutter_controller_ = nullptr;
  }

  Win32Window::OnDestroy();
}

LRESULT
FlutterWindow::MessageHandler(HWND hwnd, UINT const message,
                              WPARAM const wparam,
                              LPARAM const lparam) noexcept {
  // Give Flutter, including plugins, an opportunity to handle window messages.
  if (flutter_controller_) {
    std::optional<LRESULT> result =
        flutter_controller_->HandleTopLevelWindowProc(hwnd, message, wparam,
                                                      lparam);
    if (result) {
      return *result;
    }
  }

  switch (message) {
  case WM_FONTCHANGE:
    flutter_controller_->engine()->ReloadSystemFonts();
    break;
  }

  return Win32Window::MessageHandler(hwnd, message, wparam, lparam);
}

[subzero911]

Need this too. desktop_multi_window has numerous issues.

1. Only "main" window has a window title bar. Secondary windows do not have it.
2. File I/O API doesn't work from secondary windows (path_provider, file_picker show channel error)

[subzero911]

upd.: desktop_multi_window was updated to 0.3.0 just today, and they solved both of these problems

Now desktop_multi_window is used solely for multiple windows creation, and window_manager for handling position, title, centering and so on.