Save memory and time in KFileItemModel by lazy-loading the "ItemData"

To reduce unnecessary memory comsumption and CPU usage, we only fill the
QHash<QByteArray, QVariant> if the methods data(int) or setData(int) are
called for the corresponding index, or the data is necessary for sorting
the model.

According to my tests, this patch reduces the memory usage when loading
a folder with 100,000 items by 17% in Icons View, and by 26% in Details
View.

REVIEW: 112725

2 files changed, 50 insertions, 8 deletions

diff --git a/src/kitemviews/kfileitemmodel.cpp b/src/kitemviews/kfileitemmodel.cpp
index bd905bf07..d61de00c5 100644
--- a/src/kitemviews/kfileitemmodel.cpp
+++ b/src/kitemviews/kfileitemmodel.cpp
@@ -152,7 +152,12 @@ int KFileItemModel::count() const
 QHash<QByteArray, QVariant> KFileItemModel::data(int index) const
 {
     if (index >= 0 && index < count()) {
-        return m_itemData.at(index)->values;
+        ItemData* data = m_itemData.at(index);
+        if (data->values.isEmpty()) {
+            data->values = retrieveData(data->item, data->parent);
+        }
+
+        return data->values;
     }
     return QHash<QByteArray, QVariant>();
 }
@@ -163,7 +168,7 @@ bool KFileItemModel::setData(int index, const QHash<QByteArray, QVariant>& value
         return false;
     }
 
-    QHash<QByteArray, QVariant> currentValues = m_itemData.at(index)->values;
+    QHash<QByteArray, QVariant> currentValues = data(index);
 
     // Determine which roles have been changed
     QSet<QByteArray> changedRoles;
@@ -274,12 +279,12 @@ int KFileItemModel::indexForKeyboardSearch(const QString& text, int startFromInd
 {
     startFromIndex = qMax(0, startFromIndex);
     for (int i = startFromIndex; i < count(); ++i) {
-        if (data(i)["text"].toString().startsWith(text, Qt::CaseInsensitive)) {
+        if (fileItem(i).text().startsWith(text, Qt::CaseInsensitive)) {
             return i;
         }
     }
     for (int i = 0; i < startFromIndex; ++i) {
-        if (data(i)["text"].toString().startsWith(text, Qt::CaseInsensitive)) {
+        if (fileItem(i).text().startsWith(text, Qt::CaseInsensitive)) {
             return i;
         }
     }
@@ -460,7 +465,9 @@ bool KFileItemModel::isExpanded(int index) const
 bool KFileItemModel::isExpandable(int index) const
 {
     if (index >= 0 && index < count()) {
-        return m_itemData.at(index)->values.value("isExpandable").toBool();
+        // Call data (instead of accessing m_itemData directly)
+        // to ensure that the value is initialized.
+        return data(index).value("isExpandable").toBool();
     }
     return false;
 }
@@ -1140,11 +1147,42 @@ QList<KFileItemModel::ItemData*> KFileItemModel::createItemDataList(const KUrl&
     foreach (const KFileItem& item, items) {
         ItemData* itemData = new ItemData();
         itemData->item = item;
-        itemData->values = retrieveData(item, parentItem);
         itemData->parent = parentItem;
         itemDataList.append(itemData);
     }
 
+    switch (m_sortRole) {
+    case PermissionsRole:
+    case OwnerRole:
+    case GroupRole:
+    case DestinationRole:
+    case PathRole:
+        // These roles can be determined with retrieveData, and they have to be stored
+        // in the QHash "values" for the sorting.
+        foreach (ItemData* itemData, itemDataList) {
+            itemData->values = retrieveData(itemData->item, parentItem);
+        }
+        break;
+
+    case TypeRole:
+        // At least store the data including the file type for items with known MIME type.
+        foreach (ItemData* itemData, itemDataList) {
+            const KFileItem item = itemData->item;
+            if (item.isDir() || item.isMimeTypeKnown()) {
+                itemData->values = retrieveData(itemData->item, parentItem);
+            }
+        }
+        break;
+
+    default:
+        // The other roles are either resolved by KFileItemModelRolesUpdater
+        // (this includes the SizeRole for directories), or they do not need
+        // to be stored in the QHash "values" for sorting because the data can
+        // be retrieved directly from the KFileItem (NameRole, SiezRole for files,
+        // DateRole).
+        break;
+    }
+
     return itemDataList;
 }
 
@@ -1642,7 +1680,7 @@ QList<QPair<int, QVariant> > KFileItemModel::nameRoleGroups() const
             continue;
         }
 
-        const QString name = m_itemData.at(i)->values.value("text").toString();
+        const QString name = m_itemData.at(i)->item.text();
 
         // Use the first character of the name as group indication
         QChar newFirstChar = name.at(0).toUpper();
diff --git a/src/kitemviews/kfileitemmodel.h b/src/kitemviews/kfileitemmodel.h
index 841016138..50e3e326b 100644
--- a/src/kitemviews/kfileitemmodel.h
+++ b/src/kitemviews/kfileitemmodel.h
@@ -492,7 +492,11 @@ private:
 
 inline bool KFileItemModel::isChildItem(int index) const
 {
-    return m_requestRole[ExpandedParentsCountRole] && m_itemData.at(index)->values.value("expandedParentsCount").toInt() > 0;
+    if (m_itemData.at(index)->parent) {
+        return true;
+    } else {
+        return false;
+    }
 }
 
 #endif