some more fixes

Removed QmlExpression from api
On activation of template box, we overwrite the text in the GUI
The preview is loaded including expression values on start
Takes expression instead of currentText from ExpressionWidget - means it delivers fields in quotes

python/gui/auto_generated/editorwidgets/qgsqmlwidgetwrapper.sip.in

@@ -58,26 +58,7 @@ passes the ``feature`` into the context property of the widget
 
 };
 
-class QmlExpression : QObject
-{
-%Docstring
-To pass the QgsExpression functionality and it's context to the context of the QQuickWidget
-
-.. versionadded:: 3.4
-%End
-
-%TypeHeaderCode
-#include "qgsqmlwidgetwrapper.h"
-%End
-  public:
-    void setExpressionContext( const QgsExpressionContext &context );
 
-    QVariant evaluate( const QString &expression ) const;
-%Docstring
-evaluates the value regarding the /a expression and the context
-%End
-
-};
 
 /************************************************************************
  * This file has been generated automatically from                      *

src/app/qgsattributesformproperties.cpp

@@ -1124,14 +1124,14 @@ void DnDTree::onItemDoubleClicked( QTreeWidgetItem *item, int column )
       qmlCode->setPlaceholderText( tr( "Insert QML code here..." ) );
 
       QgsQmlWidgetWrapper *qmlWrapper = new QgsQmlWidgetWrapper( mLayer, nullptr, this );
-      qmlWrapper->setQmlCode( qmlCode->toPlainText() );
+      QgsFeature previewFeature;
+      mLayer->getFeatures().nextFeature( previewFeature );
+
       //update preview on text change
       connect( qmlCode, &QPlainTextEdit::textChanged, this, [ = ]
       {
         qmlWrapper->setQmlCode( qmlCode->toPlainText() );
         qmlWrapper->reinitWidget();
-        QgsFeature previewFeature;
-        mLayer->getFeatures().nextFeature( previewFeature );
         qmlWrapper->setFeature( previewFeature );
       } );
 
@@ -1141,7 +1141,7 @@ void DnDTree::onItemDoubleClicked( QTreeWidgetItem *item, int column )
       qmlObjectTemplate->addItem( tr( "Rectangle" ) );
       qmlObjectTemplate->addItem( tr( "Pie chart" ) );
       qmlObjectTemplate->addItem( tr( "Bar chart" ) );
-      connect( qmlObjectTemplate, qgis::overload<int>::of( &QComboBox::currentIndexChanged ), qmlCode, [ = ]( int index )
+      connect( qmlObjectTemplate, qgis::overload<int>::of( &QComboBox::activated ), qmlCode, [ = ]( int index )
       {
         qmlCode->clear();
         switch ( index )
@@ -1215,7 +1215,7 @@ void DnDTree::onItemDoubleClicked( QTreeWidgetItem *item, int column )
 
       connect( addExpressionButton, &QAbstractButton::clicked, this, [ = ]
       {
-        qmlCode->insertPlainText( QStringLiteral( "expression.evaluate(\"%1\")" ).arg( expressionWidget->currentText().replace( '"', "\\\"" ) ) );
+        qmlCode->insertPlainText( QStringLiteral( "expression.evaluate(\"%1\")" ).arg( expressionWidget->expression().replace( '"', "\\\"" ) ) );
       } );
 
       layout->addRow( tr( "Title" ), title );
@@ -1233,6 +1233,8 @@ void DnDTree::onItemDoubleClicked( QTreeWidgetItem *item, int column )
       qmlPreviewBox->setLayout( new QGridLayout );
       qmlPreviewBox->setMinimumWidth( 400 );
       qmlPreviewBox->layout()->addWidget( qmlWrapper->widget() );
+      //emit to load preview for the first time
+      emit qmlCode->textChanged();
       qmlLayout->addWidget( qmlPreviewBox );
 
       QDialogButtonBox *buttonBox = new QDialogButtonBox( QDialogButtonBox::Ok | QDialogButtonBox::Cancel );

src/gui/editorwidgets/qgsqmlwidgetwrapper.h

@@ -63,12 +63,16 @@ class GUI_EXPORT QgsQmlWidgetWrapper : public QgsWidgetWrapper
     QQuickWidget *mWidget = nullptr;
 };
 
+
+#ifndef SIP_RUN
+///@cond PRIVATE
+
 /**
  * \ingroup gui
  * To pass the QgsExpression functionality and it's context to the context of the QQuickWidget
  * \since QGIS 3.4
  */
-class GUI_EXPORT QmlExpression : public QObject
+class QmlExpression : public QObject
 {
     Q_OBJECT
 
@@ -81,5 +85,7 @@ class GUI_EXPORT QmlExpression : public QObject
   private:
     QgsExpressionContext mExpressionContext;
 };
+///@endcond
+#endif //SIP_RUN
 
 #endif // QGSQMLWIDGETWRAPPER_H