[Split view] Reset splitter position on double click

This commit makes Dolphin to reset the position of the Split View splitter
on double-click.

BUG: 206525
FIXED-IN: 21.12

src/dolphintabpage.cpp

@@ -12,7 +12,6 @@
 #include "global.h"
 
 #include <QVariantAnimation>
-#include <QSplitter>
 #include <QGridLayout>
 #include <QWidgetAction>
 #include <QStyle>
@@ -28,7 +27,7 @@ DolphinTabPage::DolphinTabPage(const QUrl &primaryUrl, const QUrl &secondaryUrl,
     layout->setSpacing(0);
     layout->setContentsMargins(0, 0, 0, 0);
 
-    m_splitter = new QSplitter(Qt::Horizontal, this);
+    m_splitter = new DolphinTabPageSplitter(Qt::Horizontal, this);
     m_splitter->setChildrenCollapsible(false);
     connect(m_splitter, &QSplitter::splitterMoved,
             this, &DolphinTabPage::splitterMoved);
@@ -505,3 +504,47 @@ void DolphinTabPage::startExpandViewAnimation(DolphinViewContainer *expandingCon
     }
     m_expandViewAnimation->start(QAbstractAnimation::DeleteWhenStopped);
 }
+
+DolphinTabPageSplitterHandle::DolphinTabPageSplitterHandle(Qt::Orientation orientation, QSplitter *parent)
+    : QSplitterHandle(orientation, parent)
+    , m_mouseReleaseWasReceived(false)
+{}
+
+bool DolphinTabPageSplitterHandle::event(QEvent *event)
+{
+    switch (event->type()) {
+    case QEvent::MouseButtonPress:
+        m_mouseReleaseWasReceived = false;
+        break;
+    case QEvent::MouseButtonRelease:
+        if (m_mouseReleaseWasReceived) {
+            resetSplitterSizes();
+        }
+        m_mouseReleaseWasReceived = !m_mouseReleaseWasReceived;
+        break;
+    case QEvent::MouseButtonDblClick:
+        m_mouseReleaseWasReceived = false;
+        resetSplitterSizes();
+        break;
+    default:
+        break;
+    }
+
+    return QSplitterHandle::event(event);
+}
+
+void DolphinTabPageSplitterHandle::resetSplitterSizes()
+{
+    QList<int> splitterSizes = splitter()->sizes();
+    std::fill(splitterSizes.begin(), splitterSizes.end(), 0);
+    splitter()->setSizes(splitterSizes);
+}
+
+DolphinTabPageSplitter::DolphinTabPageSplitter(Qt::Orientation orientation, QWidget *parent)
+    : QSplitter(orientation, parent)
+{}
+
+QSplitterHandle* DolphinTabPageSplitter::createHandle()
+{
+    return new DolphinTabPageSplitterHandle(orientation(), this);
+}

src/dolphintabpage.h

@@ -11,12 +11,13 @@
 #include <QPointer>
 #include <QUrl>
 #include <QWidget>
+#include <QSplitter>
 
 class DolphinNavigatorsWidgetAction;
 class DolphinViewContainer;
-class QSplitter;
 class QVariantAnimation;
 class KFileItemList;
+class DolphinTabPageSplitter;
 
 enum Animated {
     WithAnimation,
@@ -185,7 +186,7 @@ private:
     void startExpandViewAnimation(DolphinViewContainer *expandingContainer);
 
 private:
-    QSplitter* m_splitter;
+    DolphinTabPageSplitter *m_splitter;
 
     QPointer<DolphinNavigatorsWidgetAction> m_navigatorsWidget;
     QPointer<DolphinViewContainer> m_primaryViewContainer;
@@ -199,4 +200,34 @@ private:
     bool m_active;
 };
 
+class DolphinTabPageSplitterHandle : public QSplitterHandle
+{
+    Q_OBJECT
+
+public:
+    explicit DolphinTabPageSplitterHandle(Qt::Orientation orientation, QSplitter *parent);
+
+protected:
+    bool event(QEvent *event) override;
+
+private:
+    void resetSplitterSizes();
+
+    // Sometimes QSplitterHandle doesn't receive MouseButtonDblClick event.
+    // We can detect that MouseButtonDblClick event should have been
+    // received if we receive two MouseButtonRelease events in a row.
+    bool m_mouseReleaseWasReceived;
+};
+
+class DolphinTabPageSplitter : public QSplitter
+{
+    Q_OBJECT
+
+public:
+    explicit DolphinTabPageSplitter(Qt::Orientation orientation, QWidget *parent);
+
+protected:
+    QSplitterHandle* createHandle() override;
+};
+
 #endif // DOLPHIN_TAB_PAGE_H