Make wxTreeCtrl::EnsureVisible() work while frozen in wxMSW

Scrolling the item into view to make it visible didn't work since the
changes of badf6bc300, which suppressed
scrolling completely while frozen, any longer.

Work around it by remembering the item to make visible and actually
doing it when the control is thawed.

Also add menu item to call Freeze()/Thaw() on wxTreeCtrl in the sample
to make testing this and similar problems easier.

Closes #18435.

include/wx/msw/treectrl.h

@@ -315,6 +315,9 @@ private:
     // Virtual root item, if wxTR_HIDE_ROOT is set.
     void* m_pVirtualRoot;
 
+    // Item to call EnsureVisible() on when the tree is thawed, if necessary.
+    wxTreeItemId m_htEnsureVisibleOnThaw;
+
     // the starting item for selection with Shift
     wxTreeItemId m_htSelStart, m_htClickedItem;
     wxPoint m_ptClick;

samples/treectrl/treetest.cpp

@@ -111,6 +111,7 @@ wxBEGIN_EVENT_TABLE(MyFrame, wxFrame)
     MENU_LINK(DeleteChildren)
     MENU_LINK(DeleteAll)
     MENU_LINK(Recreate)
+    MENU_LINK(FreezeThaw)
     MENU_LINK(ToggleImages)
     MENU_LINK(ToggleStates)
     MENU_LINK(ToggleBell)
@@ -261,6 +262,7 @@ MyFrame::MyFrame(const wxString& title, int x, int y, int w, int h)
     style_menu->AppendSeparator();
     style_menu->Append(TreeTest_ResetStyle, "&Reset to default\tF10");
 
+    tree_menu->AppendCheckItem(TreeTest_FreezeThaw, "&Freeze the tree");
     tree_menu->Append(TreeTest_Recreate, "&Recreate the tree");
     tree_menu->Append(TreeTest_CollapseAndReset, "C&ollapse and reset");
     tree_menu->AppendSeparator();
@@ -664,6 +666,16 @@ void MyFrame::OnDeleteAll(wxCommandEvent& WXUNUSED(event))
     m_treeCtrl->DeleteAllItems();
 }
 
+void MyFrame::OnFreezeThaw(wxCommandEvent& event)
+{
+    if ( event.IsChecked() )
+        m_treeCtrl->Freeze();
+    else
+        m_treeCtrl->Thaw();
+
+    wxLogMessage("The tree is %sfrozen", m_treeCtrl->IsFrozen() ? "" : "not ");
+}
+
 void MyFrame::OnRecreate(wxCommandEvent& event)
 {
     OnDeleteAll(event);

samples/treectrl/treetest.h

@@ -215,6 +215,7 @@ public:
     void OnDeleteChildren(wxCommandEvent& event);
     void OnDeleteAll(wxCommandEvent& event);
 
+    void OnFreezeThaw(wxCommandEvent& event);
     void OnRecreate(wxCommandEvent& event);
     void OnToggleButtons(wxCommandEvent& event);
     void OnToggleImages(wxCommandEvent& event);
@@ -335,6 +336,7 @@ enum
     TreeTest_Delete,
     TreeTest_DeleteChildren,
     TreeTest_DeleteAll,
+    TreeTest_FreezeThaw,
     TreeTest_Recreate,
     TreeTest_ToggleImages,
     TreeTest_ToggleStates,

src/msw/treectrl.cpp

@@ -1724,6 +1724,7 @@ void wxTreeCtrl::DeleteAllItems()
     TreeItemUnlocker unlock_all;
 
     // invalidate all the items we store as they're going to become invalid
+    m_htEnsureVisibleOnThaw =
     m_htSelStart =
     m_htClickedItem = wxTreeItemId();
 
@@ -1996,6 +1997,16 @@ void wxTreeCtrl::EnsureVisible(const wxTreeItemId& item)
 {
     wxCHECK_RET( !IsHiddenRoot(item), wxT("can't show hidden root item") );
 
+    if ( IsFrozen() )
+    {
+        // We can't ensure that the item is visible if it involves scrolling
+        // while we're frozen, as we disable scrolling in this case. So just
+        // remember that item we were supposed to make visible and actually do
+        // it when the control is thawed.
+        m_htEnsureVisibleOnThaw = item;
+        return;
+    }
+
     // no error return
     (void)TreeView_EnsureVisible(GetHwnd(), HITEM(item));
 }
@@ -3953,6 +3964,13 @@ void wxTreeCtrl::DoThaw()
     wxMSWWinStyleUpdater(GetHwnd()).TurnOff(TVS_NOSCROLL);
 
     wxTreeCtrlBase::DoThaw();
+
+    if ( !IsFrozen() && m_htEnsureVisibleOnThaw.IsOk() )
+    {
+        // Really do the job of EnsureVisible() now that we can.
+        EnsureVisible(m_htEnsureVisibleOnThaw);
+        m_htEnsureVisibleOnThaw.Unset();
+    }
 }
 
 #endif // wxUSE_TREECTRL