LYN-4863: Item data not copied on drag-n-drop if column is hidden in Asset Browser Tree View. (#1616)

* Fixed: Item returning null in drag and drop when column is hidden

* Added explanation about why this approach is needed

Signed-off-by: John <jonawals@amazon.com>

Code/Framework/AzToolsFramework/AzToolsFramework/AssetBrowser/Views/AssetBrowserTreeView.cpp

@@ -185,10 +185,11 @@ namespace AzToolsFramework
 
         void AssetBrowserTreeView::rowsAboutToBeRemoved(const QModelIndex& parent, int start, int end)
         {
-            // if selected entry is being removed, clear selection so not to select (and attempt to preview) other entries potentially marked for deletion
+            // if selected entry is being removed, clear selection so not to select (and attempt to preview) other entries potentially
-            if (selectionModel() && selectionModel()->selectedIndexes().size() == 1)
+            // marked for deletion
+            if (selectionModel() && selectedIndexes().size() == 1)
             {
-                QModelIndex selectedIndex = selectionModel()->selectedIndexes().first();
+                QModelIndex selectedIndex = selectedIndexes().first();
                 QModelIndex parentSelectedIndex = selectedIndex.parent();
                 if (parentSelectedIndex == parent && selectedIndex.row() >= start && selectedIndex.row() <= end)
                 {
@@ -198,6 +199,14 @@ namespace AzToolsFramework
             QTreeView::rowsAboutToBeRemoved(parent, start, end);
         }
 
+        // Item data for hidden columns normally isn't copied by Qt during drag-and-drop (see QTBUG-30242).
+        // However, for the AssetBrowser, the hidden columns should get copied. By overriding selectedIndexes() to
+        // include all selected indices, not just the visible ones, we can get the behavior we're looking for.
+        QModelIndexList AssetBrowserTreeView::selectedIndexes() const
+        {
+            return selectionModel()->selectedIndexes();
+        }
+
         void AssetBrowserTreeView::SetThumbnailContext(const char* thumbnailContext) const
         {
             m_delegate->SetThumbnailContext(thumbnailContext);

Code/Framework/AzToolsFramework/AzToolsFramework/AssetBrowser/Views/AssetBrowserTreeView.h

@@ -95,6 +95,9 @@ namespace AzToolsFramework
             void selectionChanged(const QItemSelection& selected, const QItemSelection& deselected) override;
             void rowsAboutToBeRemoved(const QModelIndex& parent, int start, int end) override;
 
+        protected:
+            QModelIndexList selectedIndexes() const override;
+
         private:
             QPointer<AssetBrowserModel> m_assetBrowserModel = nullptr;
             QPointer<AssetBrowserFilterModel> m_assetBrowserSortFilterProxyModel = nullptr;