Allow QgsDataItems to override default double click behavior

python/core/qgsdataitem.sip

@@ -153,6 +153,15 @@ Create new data item.
  :rtype: bool
 %End
 
+    virtual bool handleDoubleClick();
+%Docstring
+ Called when a user double clicks on the item. Subclasses should return true
+ if they have implemented a double click handler and do not want the default
+ double click behaviour for items.
+.. versionadded:: 3.0
+ :rtype: bool
+%End
+
     virtual bool hasDragEnabled() const;
 %Docstring
  Returns true if the item may be dragged.

src/core/qgsdataitem.cpp

@@ -510,6 +510,11 @@ bool QgsDataItem::equal( const QgsDataItem *other )
            mPath == other->path() );
 }
 
+bool QgsDataItem::handleDoubleClick()
+{
+  return false;
+}
+
 QgsDataItem::State QgsDataItem::state() const
 {
   return mState;

src/core/qgsdataitem.h

@@ -155,6 +155,14 @@ class CORE_EXPORT QgsDataItem : public QObject
      */
     virtual bool handleDrop( const QMimeData * /*data*/, Qt::DropAction /*action*/ ) { return false; }
 
+    /**
+     * Called when a user double clicks on the item. Subclasses should return true
+     * if they have implemented a double click handler and do not want the default
+     * double click behaviour for items.
+     * \since QGIS 3.0
+     */
+    virtual bool handleDoubleClick();
+
     /** Returns true if the item may be dragged.
      * Default implementation returns false.
      * A draggable item has to implement mimeUri() that will be used to pass data.

src/gui/qgsbrowserdockwidget.cpp

@@ -97,7 +97,7 @@ QgsBrowserDockWidget::QgsBrowserDockWidget( const QString &name, QgsBrowserModel
   connect( mLeFilter, &QgsFilterLineEdit::textChanged, this, &QgsBrowserDockWidget::setFilter );
   connect( group, &QActionGroup::triggered, this, &QgsBrowserDockWidget::setFilterSyntax );
   connect( mBrowserView, &QgsDockBrowserTreeView::customContextMenuRequested, this, &QgsBrowserDockWidget::showContextMenu );
-  connect( mBrowserView, &QgsDockBrowserTreeView::doubleClicked, this, &QgsBrowserDockWidget::addLayerAtIndex );
+  connect( mBrowserView, &QgsDockBrowserTreeView::doubleClicked, this, &QgsBrowserDockWidget::itemDoubleClicked );
   connect( mSplitter, &QSplitter::splitterMoved, this, &QgsBrowserDockWidget::splitterMoved );
 }
 
@@ -155,6 +155,18 @@ void QgsBrowserDockWidget::showEvent( QShowEvent *e )
   QgsDockWidget::showEvent( e );
 }
 
+void QgsBrowserDockWidget::itemDoubleClicked( const QModelIndex &index )
+{
+  QgsDataItem *item = mModel->dataItem( mProxyModel->mapToSource( index ) );
+  if ( !item )
+    return;
+
+  if ( item->handleDoubleClick() )
+    return;
+  else
+    addLayerAtIndex( index ); // default double click handler
+}
+
 void QgsBrowserDockWidget::showContextMenu( QPoint pt )
 {
   QModelIndex index = mProxyModel->mapToSource( mBrowserView->indexAt( pt ) );

src/gui/qgsbrowserdockwidget.h

@@ -110,6 +110,9 @@ class GUI_EXPORT QgsBrowserDockWidget : public QgsDockWidget, private Ui::QgsBro
     //! Show event override
     void showEvent( QShowEvent *event ) override;
 
+  private slots:
+    void itemDoubleClicked( const QModelIndex &index );
+
   private:
     //! Refresh the model
     void refreshModel( const QModelIndex &index );