QMainWindow::contextMenuEvent()の代替方法：より柔軟なコンテキストメニューの実装

**Understanding contextMenuEvent()`

The contextMenuEvent() method is a virtual function inherited from the QWidget class. It is triggered whenever a right-click event occurs within the QMainWindow or any of its child widgets. This method provides an opportunity to handle the context menu behavior and customize the menu options presented to the user.

Default Context Menu Behavior

By default, QMainWindow generates a context menu that includes entries for managing toolbars and dock widgets. These entries allow users to show, hide, or lock the respective UI elements.

Customizing the Context Menu

To customize the context menu, you can override the contextMenuEvent() method in your QMainWindow subclass. Within this method, you can create a QMenu object and populate it with the desired actions. These actions can trigger specific functionalities or respond to user interactions.

Example Usage

void QMainWindow::contextMenuEvent(QContextMenuEvent *event) {
  QMenu contextMenu(this);
  QAction *newDocumentAction = contextMenu.addAction("New Document");
  connect(newDocumentAction, SIGNAL(triggered()), this, SLOT(openNewDocument()));

  contextMenu.exec(event->globalPos());
}

void QMainWindow::openNewDocument() {
  // Implement the logic for opening a new document
}

In this example, the contextMenuEvent() method creates a QMenu object and adds an action named "New Document". When the user clicks this action, the openNewDocument() slot is invoked, allowing you to implement the document creation process.

Key Considerations

• Action-Response Mechanism
  Connect the triggered() signal of each action to the corresponding slot to implement the desired behavior.

• Menu Placement
  The contextMenu.exec(event->globalPos()) statement displays the context menu at the current cursor position.

• Event Handling
  The contextMenuEvent() method receives a QContextMenuEvent object that provides information about the right-click event, such as the position of the cursor.

Conclusion

---

基本的なコンテキストメニューの作成

#include <QApplication>
#include <QMainWindow>
#include <QMenu>
#include <QAction>

class MyMainWindow : public QMainWindow {
public:
    MyMainWindow() {
        setCentralWidget(new QWidget);
    }

protected:
    void contextMenuEvent(QContextMenuEvent *event) override {
        QMenu contextMenu(this);

        // デフォルトのコンテキストメニューアクションを追加
        QMenu *defaultMenu = createPopupMenu();
        if (defaultMenu) {
            contextMenu.addMenu(defaultMenu);
        }

        // 新しいドキュメントを開くアクションを追加
        QAction *newDocumentAction = contextMenu.addAction("新しいドキュメント");
        connect(newDocumentAction, SIGNAL(triggered()), this, SLOT(openNewDocument()));

        contextMenu.exec(event->globalPos());
    }

private slots:
    void openNewDocument();
};

void MyMainWindow::openNewDocument() {
    // 新しいドキュメントを開く処理を記述
    // ...
}

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    MyMainWindow window;
    window.show();
    return app.exec();
}

チェックボックス付きアクションを使用したコンテキストメニュー

この例では、チェックボックス付きアクションを使用して、永続的に設定を保存するコンテキストメニューオプションを作成する方法を示します。

#include <QApplication>
#include <QMainWindow>
#include <QMenu>
#include <QAction>
#include <QSettings>

class MyMainWindow : public QMainWindow {
public:
    MyMainWindow() {
        setCentralWidget(new QWidget);

        // 設定ファイルの初期化
        settings = new QSettings("MyCompany", "MyApp");
    }

protected:
    void contextMenuEvent(QContextMenuEvent *event) override {
        QMenu contextMenu(this);

        // チェックボックス付きアクションの作成
        QAction *showToolbarAction = contextMenu.addAction("ツールバーを表示");
        showToolbarAction->setCheckable(true);
        showToolbarAction->setChecked(settings->value("showToolbar", true).toBool());
        connect(showToolbarAction, SIGNAL(toggled(bool)), this, SLOT(toggleToolbar(bool)));

        QAction *showStatusBarAction = contextMenu.addAction("ステータスバーを表示");
        showStatusBarAction->setCheckable(true);
        showStatusBarAction->setChecked(settings->value("showStatusBar", true).toBool());
        connect(showStatusBarAction, SIGNAL(toggled(bool)), this, SLOT(toggleStatusBar(bool)));

        contextMenu.exec(event->globalPos());
    }

private slots:
    void toggleToolbar(bool checked);
    void toggleStatusBar(bool checked);

private:
    QSettings *settings;
};

void MyMainWindow::toggleToolbar(bool checked) {
    // ツールバーの表示/非表示を制御
    toolbar->setVisible(checked);
    settings->setValue("showToolbar", checked);
}

void MyMainWindow::toggleStatusBar(bool checked) {
    // ステータスバーの表示/非表示を制御
    statusBar()->setVisible(checked);
    settings->setValue("showStatusBar", checked);
}

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    MyMainWindow window;
    window.show();
    return app.exec();
}

この例では、サブメニューを使用して、関連するアクションをグループ化するコンテキストメニューを作成する方法を示します。

#include <QApplication>
#include <QMainWindow>
#include <QMenu>
#include <QAction>

class MyMainWindow : public QMainWindow {
public:
    MyMainWindow() {
        setCentralWidget(new QWidget);
    }

protected:
    void contextMenuEvent(QContextMenuEvent *event) override {
        QMenu contextMenu(this);

        // ファイル操作サブメニュー
        QMenu *fileMenu = contextMenu.addMenu("ファイル");
        fileMenu->addAction("新規作成");
        fileMenu->addAction("開く");
        fileMenu->addAction("保存");

        // 編集操作サブメニュー
        QMenu *edit

---

1. Using QContextMenuEvent in Child Widgets
   

   Instead of overriding contextMenuEvent() in the QMainWindow class, you can implement context menu handling directly within child widgets. This approach allows for more granular control over the context menu behavior for specific UI elements.

   To achieve this, connect the contextMenuEvent() signal of the child widget to a slot in its parent or another appropriate class. Within the slot, create and customize the context menu as desired.

   // ChildWidget.h
   class ChildWidget : public QWidget {
       Q_SIGNALS:
           void contextMenuRequested(QPoint globalPos);
   };
   
   // ChildWidget.cpp
   void ChildWidget::contextMenuEvent(QContextMenuEvent *event) {
       emit contextMenuRequested(event->globalPos());
   }
   
   // MainWindow.cpp
   void MainWindow::connectChildContextMenu(ChildWidget *childWidget) {
       connect(childWidget, SIGNAL(contextMenuRequested(QPoint)),
               this, SLOT(handleChildContextMenu(QPoint)));
   }
   
   void MainWindow::handleChildContextMenu(QPoint globalPos) {
       // Create and display the context menu at the specified position
       QMenu contextMenu(this);
       // ... (Add menu items and actions)
       contextMenu.exec(globalPos);
   }
   

2. Using QObject::installEventFilter()
   

   The QObject::installEventFilter() method allows you to intercept and filter events for any object in the Qt application hierarchy. By installing an event filter on the QMainWindow or a relevant parent widget, you can gain control over context menu events and handle them as needed.

   class MyEventFilter : public QObject {
   public:
       MyEventFilter(QObject *object) : QObject(object) {}
   
       bool eventFilter(QObject *watched, QEvent *event) override {
           if (event->type() == QEvent::ContextMenu) {
               // Handle context menu event here
               QContextMenuEvent *contextMenuEvent = static_cast<QContextMenuEvent *>(event);
               // ... (Create and display the context menu)
               return true; // Prevent default context menu behavior
           }
           return QObject::eventFilter(watched, event);
       }
   };
   
   // MainWindow.cpp
   void MainWindow::setupEventFilter() {
       eventFilter = new MyEventFilter(this);
       installEventFilter(eventFilter);
   }