Add Qt.callLater() function.

Calling the new Qt.callLater() multiple times in quick succession with the same
JS function as argument will result in a single call to that function, thus
eliminating redundant unnecessary calls.

Based on previous patches by Mathias Malmqvist <mathias.malmqvist@nokia.com>
and Chris Adams <chris.adams@jollamobile.com>

Change-Id: Ie71b60d4d48fa73d3deae723775cf36662d199ae
Task-number: QTBUG-22400
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

1 files changed, 109 insertions, 0 deletions

diff --git a/src/qml/doc/snippets/qml/qtLater.qml b/src/qml/doc/snippets/qml/qtLater.qml
new file mode 100644
index 0000000000..e2bc02edb4
--- /dev/null
+++ b/src/qml/doc/snippets/qml/qtLater.qml
@@ -0,0 +1,109 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick 2.0
+
+Rectangle {
+    width: 480
+    height: 320
+
+    property int callsToUpdateMinimumWidth: 0
+    property bool optimize: true
+
+    property int currentTextModel: 0
+    property var columnTexts: [
+        ["Click on either", "rectangle above", "and note how the counter", "below updates", "significantly faster using the", "regular (non-optimized)", "implementation"],
+        ["The width", "of this column", "is", "no wider than the", "widest item"],
+        ["Note how using Qt.callLater()", "the minimum width is", "calculated a bare-minimum", "number", "of times"]
+    ]
+
+    Text {
+        x: 20; y: 280
+        text: "Times minimum width has been calculated: " + callsToUpdateMinimumWidth
+    }
+
+    Row {
+        y: 25; spacing: 30; anchors.horizontalCenter: parent.horizontalCenter
+        Rectangle {
+            width: 200; height:  50; color: "lightgreen"
+            Text { text: "Optimized behavior\nusing Qt.callLater()"; anchors.centerIn: parent }
+            MouseArea { anchors.fill: parent; onClicked: { optimize = true; currentTextModel++ } }
+        }
+        Rectangle {
+            width: 200; height:  50; color: "lightblue"
+            Text { text: "Regular behavior"; anchors.centerIn: parent}
+            MouseArea { anchors.fill: parent; onClicked: { optimize = false; currentTextModel++ } }
+        }
+    }
+
+    Column {
+        id: column
+        anchors.centerIn: parent
+
+        onChildrenChanged: optimize ? Qt.callLater(updateMinimumWidth) : updateMinimumWidth()
+
+        property int widestChild
+        function updateMinimumWidth() {
+            callsToUpdateMinimumWidth++
+            var w = 0;
+            for (var i in children) {
+                var child = children[i];
+                if (child.implicitWidth > w) {
+                    w = child.implicitWidth;
+                }
+            }
+
+            widestChild = w;
+        }
+
+        Repeater {
+            id: repeater
+            model: columnTexts[currentTextModel%3]
+            delegate: Text {
+                color: "white"
+                text: modelData
+                width: column.widestChild
+                horizontalAlignment: Text.Center
+                Rectangle { anchors.fill: parent; z: -1; color: index%2 ? "gray" : "darkgray" }
+            }
+        }
+    }
+}
+//![0]