QmlDesigner.ItemLibrary: Start drag using QTimer::singleShot()

A drag might change the imports which invalidates the model exposed
to qml. Since QObjects are deleted when the model is reseted this did lead to
a crash in the qml engine, because the object emitting the signal was deleted.
To avoid this we call startDragAndDrop() asynchronously using QTimer::singleShot().
Now the object is always deleted after the signal is emitted not during the emit.

Task-number: QTCREATORBUG-11139

Change-Id: I92e7f9dfff33697b9ff0da148dc9da629723ab7e
Reviewed-by: Marco Bubke <marco.bubke@digia.com>

2 files changed, 16 insertions, 6 deletions

diff --git a/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp b/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp
index 99e92d88ea..e715e9800e 100644
--- a/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp
+++ b/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp
@@ -48,6 +48,7 @@
 #include <QWheelEvent>
 #include <QMenu>
 #include <QApplication>
+#include <QTimer>
 
 #include <QQuickItem>
 
@@ -64,7 +65,8 @@ ItemLibraryWidget::ItemLibraryWidget(QWidget *parent) :
     m_resIconSize(24, 24),
     m_itemsView(new QQuickView()),
     m_resourcesView(new Internal::ItemLibraryTreeView(this)),
-    m_filterFlag(QtBasic)
+    m_filterFlag(QtBasic),
+    m_itemLibraryId(-1)
 {
     Internal::registerQmlTypes();
 
@@ -91,7 +93,7 @@ ItemLibraryWidget::ItemLibraryWidget(QWidget *parent) :
 
     QQuickItem *rootItem = qobject_cast<QQuickItem*>(m_itemsView->rootObject());
     connect(rootItem, SIGNAL(itemSelected(int)), this, SLOT(showItemInfo(int)));
-    connect(rootItem, SIGNAL(itemDragged(int)), this, SLOT(startDragAndDrop(int)));
+    connect(rootItem, SIGNAL(itemDragged(int)), this, SLOT(startDragAndDropDelayed(int)));
     connect(this, SIGNAL(scrollItemsView(QVariant)), rootItem, SLOT(scrollView(QVariant)));
     connect(this, SIGNAL(resetItemsView()), rootItem, SLOT(resetView()));
 
@@ -363,12 +365,18 @@ void ItemLibraryWidget::setResourcePath(const QString &resourcePath)
     updateSearch();
 }
 
-void ItemLibraryWidget::startDragAndDrop(int itemLibId)
+void ItemLibraryWidget::startDragAndDropDelayed(int itemLibraryId)
 {
-    QMimeData *mimeData = m_itemLibraryModel->getMimeData(itemLibId);
+    m_itemLibraryId = itemLibraryId;
+    QTimer::singleShot(0, this, SLOT(startDragAndDrop()));
+}
+
+void ItemLibraryWidget::startDragAndDrop()
+{
+    QMimeData *mimeData = m_itemLibraryModel->getMimeData(m_itemLibraryId);
     QDrag *drag = new QDrag(this);
 
-    drag->setPixmap(m_itemLibraryModel->getIcon(itemLibId).pixmap(32, 32));
+    drag->setPixmap(m_itemLibraryModel->getIcon(m_itemLibraryId).pixmap(32, 32));
     drag->setMimeData(mimeData);
 
     drag->exec();
diff --git a/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.h b/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.h
index 0369771d12..8b121472aa 100644
--- a/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.h
+++ b/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.h
@@ -94,7 +94,8 @@ public slots:
 
     void setResourcePath(const QString &resourcePath);
 
-    void startDragAndDrop(int itemLibId);
+    void startDragAndDropDelayed(int itemLibId);
+    void startDragAndDrop();
     void showItemInfo(int itemLibId);
 
     void setModel(Model *model);
@@ -137,6 +138,7 @@ private:
 
     QWeakPointer<Model> m_model;
     FilterChangeFlag m_filterFlag;
+    int m_itemLibraryId;
 };
 
 }