WelcomePage: optimizing GridView

Instead of placing the "complete" GridView to a ScrollArea we now add
a ScrollBar to the GridView. This means that only visible delegates are
instanciated and the GridView gets alot faster.

Change-Id: I63b8593b260acd4d3a786a99c7dd58507c12e221
Reviewed-by: Alessandro Portale <alessandro.portale@nokia.com>

share/qtcreator/welcomescreen/examples.qml

@@ -52,18 +52,14 @@ Rectangle {
         caption: qsTr("Examples")
     }
 
-    CustomScrollArea {
-        id: scrollArea;
-
+    CustomizedGridView {
         anchors.rightMargin: 38
         anchors.bottomMargin: 60
         anchors.leftMargin: 38
         anchors.topMargin: 102
         anchors.fill: parent
 
-        CustomizedGridView {
-            model: examplesModel
-        }
+        model: examplesModel
     }
 
     SearchBar {

share/qtcreator/welcomescreen/tutorials.qml

@@ -52,23 +52,14 @@ Rectangle {
         caption: qsTr("Tutorials")
     }
 
-    CustomScrollArea {
-        id: scrollArea;
-
+    CustomizedGridView {
         anchors.rightMargin: 38
         anchors.bottomMargin: 60
         anchors.leftMargin: 38
         anchors.topMargin: 102
         anchors.fill: parent
 
-        clip: true
-
-        horizontalScrollBar.visible: false
-        frame: false
-
-        CustomizedGridView {
-            model: tutorialsModel
-        }
+        model: tutorialsModel
     }
 
     SearchBar {

share/qtcreator/welcomescreen/widgets/CustomScrollArea.qml

-/**************************************************************************
-**
-** This file is part of Qt Creator
-**
-** Copyright (c) 2011 Nokia Corporation and/or its subsidiary(-ies).
-**
-** Contact: Nokia Corporation (qt-info@nokia.com)
-**
-**
-** GNU Lesser General Public License Usage
-**
-** This file may be used under the terms of the GNU Lesser General Public
-** License version 2.1 as published by the Free Software Foundation and
-** appearing in the file LICENSE.LGPL included in the packaging of this file.
-** Please review the following information to ensure the GNU Lesser General
-** Public License version 2.1 requirements will be met:
-** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
-**
-** In addition, as a special exception, Nokia gives you certain additional
-** rights. These rights are described in the Nokia Qt LGPL Exception
-** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
-**
-** Other Usage
-**
-** Alternatively, this file may be used in accordance with the terms and
-** conditions contained in a signed written agreement between you and Nokia.
-**
-** If you have questions regarding the use of this file, please contact
-** Nokia at qt-info@nokia.com.
-**
-**************************************************************************/
-
-import QtQuick 1.1
-import qtcomponents 1.0
-
-ScrollArea {
-    horizontalScrollBar.visible: false
-    frame: false
-    clip: true
-}

share/qtcreator/welcomescreen/widgets/CustomizedGridView.qml

@@ -31,14 +31,16 @@
 **************************************************************************/
 
 import QtQuick 1.0
+import qtcomponents 1.0
 
 GridView {
+    id: gridView
     interactive: false
-    width: scrollArea.width
+    clip: true
     cellHeight: 240
     cellWidth: 216
     property int columns:  Math.max(Math.floor(width / cellWidth), 1)
-    height: 240 * Math.ceil(count / columns)
+    cacheBuffer: 1000
 
     x: Math.max((width - (cellWidth * columns)) / 2, 0);
 
@@ -61,4 +63,28 @@ GridView {
         tags: model.tags
     }
 
+    WheelArea {
+        id: wheelarea
+        anchors.fill: parent
+        verticalMinimumValue: vscrollbar.minimumValue
+        verticalMaximumValue: vscrollbar.maximumValue
+
+        onVerticalValueChanged: gridView.contentY = verticalValue
+    }
+
+    ScrollBar {
+        id: vscrollbar
+        orientation: Qt.Vertical
+        property int availableHeight : gridView.height
+        visible: contentHeight > availableHeight
+        maximumValue: contentHeight > availableHeight ? gridView.contentHeight - availableHeight : 0
+        minimumValue: 0
+        anchors.right: parent.right
+        anchors.top: parent.top
+        anchors.bottom: parent.bottom
+        anchors.topMargin: styleitem.style == "mac" ? 1 : 0
+        onValueChanged: gridView.contentY = value
+        anchors.rightMargin: styleitem.frameoffset
+        anchors.bottomMargin: hscrollbar.visible ? hscrollbar.height : styleitem.frameoffset
+    }
 }