QmlDesigner: Check if root element is a graphical item

If the root element is not a graphical item, then we show a proper error
message.

Task-number: QTCREATORBUG-20014
Change-Id: I9c1ccbbeb6765bd098344ceef8024a703a8dc919
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmldesigner/components/formeditor/formeditorview.cpp

@@ -44,6 +44,7 @@
 #include <model.h>
 #include <nodeabstractproperty.h>
 #include <nodelistproperty.h>
+#include <nodemetainfo.h>
 #include <rewriterview.h>
 #include <zoomaction.h>
 
@@ -159,6 +160,8 @@ void FormEditorView::setupFormEditorItemTree(const QmlItemNode &qmlItemNode)
             if (QmlItemNode::isValidQmlItemNode(nextNode) && nextNode.modelNode().nodeSourceType() == ModelNode::NodeWithoutSource)
                 setupFormEditorItemTree(nextNode.toQmlItemNode());
     }
+
+    checkRootModelNode();
 }
 
 static void deleteWithoutChildren(const QList<FormEditorItem*> &items)
@@ -296,7 +299,11 @@ void FormEditorView::rootNodeTypeChanged(const QString &/*type*/, int /*majorVer
     if (newItemNode.isValid()) //only setup QmlItems
         setupFormEditorItemTree(newItemNode);
 
+
+
     m_currentTool->setItems(scene()->itemsForQmlItemNodes(toQmlItemNodeList(selectedModelNodes())));
+
+    checkRootModelNode();
 }
 
 void FormEditorView::propertiesAboutToBeRemoved(const QList<AbstractProperty>& propertyList)
@@ -464,6 +471,8 @@ void FormEditorView::documentMessagesChanged(const QList<DocumentMessage> &error
         m_formEditorWidget->showErrorMessageBox(errors);
     else
         m_formEditorWidget->hideErrorMessageBox();
+
+    checkRootModelNode();
 }
 
 void FormEditorView::customNotification(const AbstractView * /*view*/, const QString &identifier, const QList<ModelNode> &/*nodeList*/, const QList<QVariant> &/*data*/)
@@ -796,6 +805,8 @@ void FormEditorView::setupFormEditorWidget()
 
     if (!rewriterView()->warnings().isEmpty())
         m_formEditorWidget->showWarningMessageBox(rewriterView()->warnings());
+
+    checkRootModelNode();
 }
 
 QmlItemNode findRecursiveQmlItemNode(const QmlObjectNode &firstQmlObjectNode)
@@ -884,6 +895,21 @@ void FormEditorView::addOrRemoveFormEditorItem(const ModelNode &node)
     }
 }
 
+void FormEditorView::checkRootModelNode()
+{
+    if (m_formEditorWidget->errorMessageBoxIsVisible())
+        return;
+
+    QTC_ASSERT(rootModelNode().isValid(), return);
+
+    if (!rootModelNode().metaInfo().isGraphicalItem())
+        m_formEditorWidget->showErrorMessageBox(
+            {DocumentMessage(tr("%1 is not supported as the root element by Form Editor.")
+                                 .arg(rootModelNode().simplifiedTypeName()))});
+    else
+        m_formEditorWidget->hideErrorMessageBox();
+}
+
 void FormEditorView::reset()
 {
    QTimer::singleShot(200, this, &FormEditorView::delayedReset);

src/plugins/qmldesigner/components/formeditor/formeditorview.h

@@ -149,6 +149,7 @@ private:
     void temporaryBlockView(int duration = 1000);
     void resetNodeInstanceView();
     void addOrRemoveFormEditorItem(const ModelNode &node);
+    void checkRootModelNode();
 
     QPointer<FormEditorWidget> m_formEditorWidget;
     QPointer<FormEditorScene> m_scene;

src/plugins/qmldesigner/components/formeditor/formeditorwidget.cpp

@@ -549,6 +549,11 @@ FormEditorGraphicsView *FormEditorWidget::graphicsView() const
     return m_graphicsView;
 }
 
+bool FormEditorWidget::errorMessageBoxIsVisible() const
+{
+    return m_documentErrorWidget && m_documentErrorWidget->isVisible();
+}
+
 DocumentWarningWidget *FormEditorWidget::errorWidget()
 {
     if (m_documentErrorWidget.isNull()) {

src/plugins/qmldesigner/components/formeditor/formeditorwidget.h

@@ -89,6 +89,8 @@ public:
 
     FormEditorGraphicsView *graphicsView() const;
 
+    bool errorMessageBoxIsVisible() const;
+
 protected:
     QActionGroup *toolActionGroup() const;
     DocumentWarningWidget *errorWidget();