Add wxGridSelection::SelectAll() and use it in wxGrid

The difference between calling SelectAll() and SelectBlock() with a
block covering the entire grid is that the former discards any
previously selected blocks, which become clearly redundant.

As a consequence, clicking on the grid corner 10 times in a row still
results in a selection with a single block, not 10 (identical) blocks.

include/wx/generic/gridsel.h

@@ -52,6 +52,10 @@ public:
                     kbd, sendEvent);
     }
 
+    // This function replaces all the existing selected blocks (which become
+    // redundant) with a single block covering the entire grid.
+    void SelectAll();
+
     void DeselectBlock(const wxGridBlockCoords& block,
                        const wxKeyboardState& kbd = wxKeyboardState(),
                        bool sendEvent = true );

src/generic/grid.cpp

@@ -10235,11 +10235,8 @@ void wxGrid::SelectBlock(int topRow, int leftCol, int bottomRow, int rightCol,
 
 void wxGrid::SelectAll()
 {
-    if ( m_numRows > 0 && m_numCols > 0 )
-    {
-        if ( m_selection )
-            m_selection->SelectBlock( 0, 0, m_numRows - 1, m_numCols - 1 );
-    }
+    if ( m_selection )
+        m_selection->SelectAll();
 }
 
 // ----------------------------------------------------------------------------

src/generic/gridsel.cpp

@@ -194,6 +194,23 @@ void wxGridSelection::SelectBlock( int topRow, int leftCol,
            kbd, sendEvent);
 }
 
+void
+wxGridSelection::SelectAll()
+{
+    // There is no need to refresh anything, as Select() will do it anyhow, and
+    // no need to generate any events, so do not call ClearSelection() here.
+    m_selection.clear();
+
+    const int numRows = m_grid->GetNumberRows();
+    const int numCols = m_grid->GetNumberCols();
+
+    if ( numRows && numCols )
+    {
+        Select(wxGridBlockCoords(0, 0, numRows - 1, numCols - 1),
+               wxKeyboardState(), true /* send event */);
+    }
+}
+
 void
 wxGridSelection::DeselectBlock(const wxGridBlockCoords& block,
                                const wxKeyboardState& kbd,