Dialogs: don't create platform helpers unconditionally

No matter if Qt::AA_DontUseNativeDialogs was set, both QFileDialog and
QColorDialog were always unconditionally creating the platform helper
at construction time:

    QFooDialog()
    -> QFooDialogPrivate::init()
    -> QFooDialogPrivate::platformFooHelper()
    -> QDialogPrivate::platformHelper()

Only QFontDialog had the platformHelper() calls guarded with
canBeNativeDialog(). => Move the canBeNativeDialog() check inside
QDialogPrivate::platformHelper() where the platform helper
instance is created.

Task-number: QTBUG-55276
Change-Id: I84b595fbd009c70a3a1976ddbb32a835270c5203
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

3 files changed, 6 insertions, 10 deletions

diff --git a/src/widgets/dialogs/qdialog.cpp b/src/widgets/dialogs/qdialog.cpp
index bfc943966f..8a26e1b2a7 100644
--- a/src/widgets/dialogs/qdialog.cpp
+++ b/src/widgets/dialogs/qdialog.cpp
@@ -95,7 +95,7 @@ QPlatformDialogHelper *QDialogPrivate::platformHelper() const
 {
     // Delayed creation of the platform, ensuring that
     // that qobject_cast<> on the dialog works in the plugin.
-    if (!m_platformHelperCreated) {
+    if (!m_platformHelperCreated && canBeNativeDialog()) {
         m_platformHelperCreated = true;
         QDialogPrivate *ncThis = const_cast<QDialogPrivate *>(this);
         QDialog *dialog = ncThis->q_func();
diff --git a/src/widgets/dialogs/qfiledialog.cpp b/src/widgets/dialogs/qfiledialog.cpp
index acda6bac3e..bee73c6649 100644
--- a/src/widgets/dialogs/qfiledialog.cpp
+++ b/src/widgets/dialogs/qfiledialog.cpp
@@ -2800,7 +2800,7 @@ void QFileDialogPrivate::init(const QUrl &directory, const QString &nameFilter,
     }
 
     q->setAcceptMode(QFileDialog::AcceptOpen);
-    nativeDialogInUse = (canBeNativeDialog() && platformFileDialogHelper() != 0);
+    nativeDialogInUse = platformFileDialogHelper() != 0;
     if (!nativeDialogInUse)
         createWidgets();
     q->setFileMode(QFileDialog::AnyFile);
diff --git a/src/widgets/dialogs/qfontdialog.cpp b/src/widgets/dialogs/qfontdialog.cpp
index 2a500d3a08..c373bcf1df 100644
--- a/src/widgets/dialogs/qfontdialog.cpp
+++ b/src/widgets/dialogs/qfontdialog.cpp
@@ -824,10 +824,8 @@ void QFontDialog::setCurrentFont(const QFont &font)
     d->strikeout->setChecked(font.strikeOut());
     d->underline->setChecked(font.underline());
     d->updateFamilies();
-    if (d->canBeNativeDialog()) {
-        if (QPlatformFontDialogHelper *helper = d->platformFontDialogHelper())
-            helper->setCurrentFont(font);
-    }
+    if (QPlatformFontDialogHelper *helper = d->platformFontDialogHelper())
+        helper->setCurrentFont(font);
 }
 
 /*!
@@ -840,10 +838,8 @@ void QFontDialog::setCurrentFont(const QFont &font)
 QFont QFontDialog::currentFont() const
 {
     Q_D(const QFontDialog);
-    if (d->canBeNativeDialog()) {
-        if (const QPlatformFontDialogHelper *helper = d->platformFontDialogHelper())
-            return helper->currentFont();
-    }
+    if (const QPlatformFontDialogHelper *helper = d->platformFontDialogHelper())
+        return helper->currentFont();
     return d->sampleEdit->font();
 }