QQuickSpinBox: create JS callbacks lazily

Calling QJSEngine::evaluate() is a heavy operation. Only one of them,
namely textFromValue, is used from QML, so there's a good chance that
valueFromText doesn't need to be evaluated at component creation time.
This change postpones the initial evaluation to the point where either
callback is requested.

Before:

    RESULT : tst_CreationTime::controls():"SpinBox":
         0.53 msecs per iteration (total: 68, iterations: 128)

After:

    RESULT : tst_CreationTime::controls():"SpinBox":
         0.39 msecs per iteration (total: 51, iterations: 128)

Change-Id: I1730dc4024d0a556ca2da765ac3c52ba8a29f743
Reviewed-by: Mitch Curtis <mitch.curtis@theqtcompany.com>

2 files changed, 12 insertions, 16 deletions

diff --git a/src/templates/qquickspinbox.cpp b/src/templates/qquickspinbox.cpp
index 33ea6e79..bda955d0 100644
--- a/src/templates/qquickspinbox.cpp
+++ b/src/templates/qquickspinbox.cpp
@@ -116,8 +116,8 @@ public:
     QQuickSpinButton *up;
     QQuickSpinButton *down;
     QValidator *validator;
-    QJSValue textFromValue;
-    QJSValue valueFromText;
+    mutable QJSValue textFromValue;
+    mutable QJSValue valueFromText;
 };
 
 int QQuickSpinBoxPrivate::boundValue(int value) const
@@ -384,6 +384,11 @@ void QQuickSpinBox::setValidator(QValidator *validator)
 QJSValue QQuickSpinBox::textFromValue() const
 {
     Q_D(const QQuickSpinBox);
+    if (!d->textFromValue.isCallable()) {
+        QQmlEngine *engine = qmlEngine(this);
+        if (engine)
+            d->textFromValue = engine->evaluate(QStringLiteral("function(value, locale) { return Number(value).toLocaleString(locale, 'f', 0); }"));
+    }
     return d->textFromValue;
 }
 
@@ -420,6 +425,11 @@ void QQuickSpinBox::setTextFromValue(const QJSValue &callback)
 QJSValue QQuickSpinBox::valueFromText() const
 {
     Q_D(const QQuickSpinBox);
+    if (!d->valueFromText.isCallable()) {
+        QQmlEngine *engine = qmlEngine(this);
+        if (engine)
+            d->valueFromText = engine->evaluate(QStringLiteral("function(text, locale) { return Number.fromLocaleString(locale, text); }"));
+    }
     return d->valueFromText;
 }
 
@@ -587,19 +597,6 @@ void QQuickSpinBox::timerEvent(QTimerEvent *event)
     }
 }
 
-void QQuickSpinBox::componentComplete()
-{
-    Q_D(QQuickSpinBox);
-    QQuickControl::componentComplete();
-    QQmlEngine *engine = qmlEngine(this);
-    if (engine) {
-        if (!d->textFromValue.isCallable())
-            setTextFromValue(engine->evaluate(QStringLiteral("function(value, locale) { return Number(value).toLocaleString(locale, 'f', 0); }")));
-        if (!d->valueFromText.isCallable())
-            setValueFromText(engine->evaluate(QStringLiteral("function(text, locale) { return Number.fromLocaleString(locale, text); }")));
-    }
-}
-
 void QQuickSpinBox::itemChange(ItemChange change, const ItemChangeData &value)
 {
     Q_D(QQuickSpinBox);
diff --git a/src/templates/qquickspinbox_p.h b/src/templates/qquickspinbox_p.h
index 0ad5e70d..c7d1f6c6 100644
--- a/src/templates/qquickspinbox_p.h
+++ b/src/templates/qquickspinbox_p.h
@@ -121,7 +121,6 @@ protected:
     void mouseUngrabEvent() Q_DECL_OVERRIDE;
     void timerEvent(QTimerEvent *event) Q_DECL_OVERRIDE;
 
-    void componentComplete() Q_DECL_OVERRIDE;
     void itemChange(ItemChange change, const ItemChangeData &value) Q_DECL_OVERRIDE;
     void contentItemChange(QQuickItem *newItem, QQuickItem *oldItem) Q_DECL_OVERRIDE;