Add option to auto-show selection view

The SelectionView dock window was already an observer of the current selection
when it was showing. This changes it to continuously monitor the selection even
when invisible. If the user sets the parameter
BaseApp/Preferences/Selection/AutoShowSelectionView to true, when there is an item
selected, the view will show itself if it was hidden, and will re-hide itself when
the selection is cleared. The option has no effect if the user had chosen to manually
show the selection view prior to beginning a selection.

src/Gui/SelectionView.cpp

@@ -55,8 +55,9 @@ using namespace Gui::DockWnd;
 
 SelectionView::SelectionView(Gui::Document* pcDocument, QWidget *parent)
   : DockWindow(pcDocument,parent)
-  , SelectionObserver(false,0)
+  , SelectionObserver(true,0)
   , x(0.0f), y(0.0f), z(0.0f)
+  , openedAutomatically(false)
 {
     setWindowTitle(tr("Selection View"));
 
@@ -128,6 +129,22 @@ void SelectionView::leaveEvent(QEvent *)
 /// @cond DOXERR
 void SelectionView::onSelectionChanged(const SelectionChanges &Reason)
 {
+    ParameterGrp::handle hGrp = App::GetApplication().GetUserParameter().GetGroup("BaseApp")
+        ->GetGroup("Preferences")->GetGroup("Selection");
+    bool autoShow = hGrp->GetBool("AutoShowSelectionView", false);
+    hGrp->SetBool("AutoShowSelectionView", autoShow); // Remove this line once the preferences window item is implemented
+
+    if (autoShow) {
+        if (!parentWidget()->isVisible() && Selection().hasSelection()) {
+            parentWidget()->show();
+            openedAutomatically = true;
+        }
+        else if (openedAutomatically && !Selection().hasSelection()) {
+            parentWidget()->hide();
+            openedAutomatically = false;
+        }
+    }
+
     QString selObject;
     QTextStream str(&selObject);
     if (Reason.Type == SelectionChanges::AddSelection) {
@@ -608,14 +625,10 @@ bool SelectionView::onMsg(const char* /*pMsg*/,const char** /*ppReturn*/)
 }
 
 void SelectionView::hideEvent(QHideEvent *ev) {
-    FC_TRACE(this << " detaching selection observer");
-    this->detachSelection();
     DockWindow::hideEvent(ev);
 }
 
 void SelectionView::showEvent(QShowEvent *ev) {
-    FC_TRACE(this << " attaching selection observer");
-    this->attachSelection();
     enablePickList->setChecked(Selection().needPickedList());
     Gui::DockWindow::showEvent(ev);
 }

src/Gui/SelectionView.h

@@ -110,6 +110,7 @@ private:
 private:
     float x,y,z;
     std::vector<App::DocumentObject*> searchList;
+    bool openedAutomatically;
 };
 
 } // namespace DockWnd