Try to avoid calling the model's data method if only "text" is needed

Currently, KStandardItemListWidgetInformant::itemSizeHint() calls the
model's data(int) method for every single item, but the full data is
actually only needed for the size calculation in Compact View. In
Details View, no data is needed at all to determine the size required
for the item, and in Icons View, only the name is needed.

This patch makes it possible for subclasses of
KStandardItemListWidgetInformant to provide an alternative way to
obtain the "text", and implements this in the subclass
KFileItemListWidgetInformant.

The final goal is to achieve that the QHash which contains all data
for a file item is only created if it is really needed, e.g., because
the view needs access to the data for displaying the item on the
screen.

REVIEW: 112253

4 files changed, 28 insertions, 2 deletions

diff --git a/src/kitemviews/kfileitemlistwidget.cpp b/src/kitemviews/kfileitemlistwidget.cpp
index 3a7724134..688a4da08 100644
--- a/src/kitemviews/kfileitemlistwidget.cpp
+++ b/src/kitemviews/kfileitemlistwidget.cpp
@@ -18,6 +18,8 @@
  ***************************************************************************/
 
 #include "kfileitemlistwidget.h"
+#include "kfileitemmodel.h"
+#include "kitemlistview.h"
 
 #include <kmimetype.h>
 #include <KDebug>
@@ -35,6 +37,15 @@ KFileItemListWidgetInformant::~KFileItemListWidgetInformant()
 {
 }
 
+QString KFileItemListWidgetInformant::itemText(int index, const KItemListView* view) const
+{
+    Q_ASSERT(qobject_cast<KFileItemModel*>(view->model()));
+    KFileItemModel* fileItemModel = static_cast<KFileItemModel*>(view->model());
+
+    const KFileItem item = fileItemModel->fileItem(index);
+    return item.text();
+}
+
 QString KFileItemListWidgetInformant::roleText(const QByteArray& role,
                                                const QHash<QByteArray, QVariant>& values) const
 {
diff --git a/src/kitemviews/kfileitemlistwidget.h b/src/kitemviews/kfileitemlistwidget.h
index 24c677828..1d7bc7f01 100644
--- a/src/kitemviews/kfileitemlistwidget.h
+++ b/src/kitemviews/kfileitemlistwidget.h
@@ -31,6 +31,7 @@ public:
     virtual ~KFileItemListWidgetInformant();
 
 protected:
+    virtual QString itemText(int index, const KItemListView* view) const;
     virtual QString roleText(const QByteArray& role, const QHash<QByteArray, QVariant>& values) const;
 };
 
diff --git a/src/kitemviews/kstandarditemlistwidget.cpp b/src/kitemviews/kstandarditemlistwidget.cpp
index bc0503663..4b9f33b6f 100644
--- a/src/kitemviews/kstandarditemlistwidget.cpp
+++ b/src/kitemviews/kstandarditemlistwidget.cpp
@@ -57,13 +57,12 @@ KStandardItemListWidgetInformant::~KStandardItemListWidgetInformant()
 
 QSizeF KStandardItemListWidgetInformant::itemSizeHint(int index, const KItemListView* view) const
 {
-    const QHash<QByteArray, QVariant> values = view->model()->data(index);
     const KItemListStyleOption& option = view->styleOption();
     const int additionalRolesCount = qMax(view->visibleRoles().count() - 1, 0);
 
     switch (static_cast<const KStandardItemListView*>(view)->itemLayout()) {
     case KStandardItemListWidget::IconsLayout: {
-        const QString text = KStringHandler::preProcessWrap(values["text"].toString());
+        const QString text = KStringHandler::preProcessWrap(itemText(index, view));
 
         const qreal itemWidth = view->itemSize().width();
         const qreal maxWidth = itemWidth - 2 * option.padding;
@@ -100,6 +99,7 @@ QSizeF KStandardItemListWidgetInformant::itemSizeHint(int index, const KItemList
         // to show all roles without horizontal clipping.
         qreal maximumRequiredWidth = 0.0;
 
+        const QHash<QByteArray, QVariant> values = view->model()->data(index);
         foreach (const QByteArray& role, view->visibleRoles()) {
             const QString text = roleText(role, values);
             const qreal requiredWidth = option.fontMetrics.width(text);
@@ -159,6 +159,11 @@ qreal KStandardItemListWidgetInformant::preferredRoleColumnWidth(const QByteArra
     return width;
 }
 
+QString KStandardItemListWidgetInformant::itemText(int index, const KItemListView* view) const
+{
+    return view->model()->data(index).value("text").toString();
+}
+
 QString KStandardItemListWidgetInformant::roleText(const QByteArray& role,
                                                    const QHash<QByteArray, QVariant>& values) const
 {
diff --git a/src/kitemviews/kstandarditemlistwidget.h b/src/kitemviews/kstandarditemlistwidget.h
index 4bf6116fd..7dd93b2b8 100644
--- a/src/kitemviews/kstandarditemlistwidget.h
+++ b/src/kitemviews/kstandarditemlistwidget.h
@@ -45,6 +45,15 @@ public:
                                            const KItemListView* view) const;
 protected:
     /**
+     * @return The value of the "text" role. The default implementation returns
+     *         view->model()->data(index)["text"]. If a derived class can
+     *         prevent the (possibly expensive) construction of the
+     *         QHash<QByteArray, QVariant> returned by KItemModelBase::data(int),
+     *         it can reimplement this function.
+     */
+    virtual QString itemText(int index, const KItemListView* view) const;
+
+    /**
      * @return String representation of the role \a role. The representation of
      *         a role might depend on other roles, so the values of all roles
      *         are passed as parameter.