DolphinMainWindow: show a banner when the user presses the shortcut of a disabled action

Currently, there's no feedback when the user presses a shortcut of a disabled
action, e.g. cut / paste in a read-only directory. This patch shows a banner
in that case.

It's implemented by enabling a QShortcut for each disabled action. the
QShortcut is deleted when the action is enabled again.

The following actions are included:
cut
paste
rename
moveToTrash
deleteWithTrashShortcut
deleted
createDir
copyToOtherView
moveToOtherView

1 files changed, 60 insertions, 0 deletions

diff --git a/src/disabledactionnotifier.h b/src/disabledactionnotifier.h
new file mode 100644
index 000000000..535e9932b
--- /dev/null
+++ b/src/disabledactionnotifier.h
@@ -0,0 +1,60 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Jin Liu <[email protected]>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#pragma once
+
+#include <QAction>
+#include <QHash>
+#include <QShortcut>
+
+/**
+ * @brief A helper class to display a notification when the user presses the shortcut of a disabled action.
+ */
+class DisabledActionNotifier : public QObject
+{
+    Q_OBJECT
+
+public:
+    DisabledActionNotifier(QObject *parent = nullptr);
+
+    /**
+     * Set the reason why the action is disabled.
+     *
+     * If the action is enabled, this function does nothing.
+     *
+     * Otherwise, it registers a shortcut, so when the user presses the shortcut for the
+     * disabled action, it emits the disabledActionTriggered() signal with the disabled
+     * action and the reason.
+     *
+     * If a reason has already been set, it will be replaced.
+     */
+    void setDisabledReason(QAction *action, QStringView reason);
+
+    /**
+     * Clear the reason if it's set before by setDisabledReason().
+     *
+     * If the action is enabled, this function does nothing.
+     *
+     * Otherwise, it unregisters any shortcut set by setDisabledReason() on the same action.
+     *
+     * When an action is disabled in two cases, but only case A needs to show the reason,
+     * then case B should call this function. Otherwise, the reason set by case A might be
+     * shown for case B.
+     */
+    void clearDisabledReason(QAction *action);
+
+Q_SIGNALS:
+    /**
+     * Emitted when the user presses the shortcut of a disabled action.
+     *
+     * @param action The disabled action.
+     * @param reason The reason set in setDisabledReason().
+     */
+    void disabledActionTriggered(const QAction *action, QString reason);
+
+private:
+    QHash<QAction *, QShortcut *> m_shortcuts;
+};