MultiGeometryWidget template class abstracts window geometry changes

widgets/MultiGeometryWidget.hpp

@@ -0,0 +1,92 @@
+#ifndef MULTI_GEOMETRY_WIDGET_HPP__
+#define MULTI_GEOMETRY_WIDGET_HPP__
+
+#include <cstddef>
+#include <utility>
+#include <array>
+
+#include <QWidget>
+#include <QByteArray>
+#include <QEvent>
+
+//
+// Class MultiGeometryWidget<N, Widget> - Decorate a QWidget type with
+// 																				switchable geometries
+//
+// The abstract base class imbues a Qt Widget type with N alternative
+// geometries. Sub-classes can initialise the currently selected
+// geometry and the initial geometries using geometries. To switch
+// geometry call select_geometry(n) which saves the current geometry
+// and switches to the n'th saved geometry.
+//
+template<std::size_t N, typename Widget=QWidget>
+class MultiGeometryWidget
+  : public Widget
+{
+public:
+  template<typename... Args>
+  explicit MultiGeometryWidget (Args&&... args)
+    : Widget {std::forward<Args> (args)...}
+    , current_geometry_ {0}
+  {
+  }
+
+  void geometries (std::size_t current
+                   , std::array<QByteArray, N> const& the_geometries = std::array<QByteArray, N> {})
+  {
+    Q_ASSERT (current < the_geometries.size ());
+    saved_geometries_ = the_geometries;
+    current_geometry_ = current;
+    Widget::restoreGeometry (saved_geometries_[current_geometry_]);
+  }
+
+  std::array<QByteArray, N> const& geometries () const {return saved_geometries_;}
+  std::size_t current () {return current_geometry_;}
+
+  // Call this to select a new geometry denoted by the 'n' argument,
+  // any actual layout changes should be made in the implementation of
+  // the change_layout operation below.
+  void select_geometry (std::size_t n)
+  {
+    Q_ASSERT (n < N);
+    auto geometry = Widget::saveGeometry ();
+    change_layout (n);
+    saved_geometries_[current_geometry_] = geometry;
+    current_geometry_ = n;
+
+    // Defer restoration of the window geometry until the layour
+    // request event has been processed, this is necessary otherwise
+    // the final geometry may be affected by widgets not shown in the
+    // new layout.
+    desired_geometry_ = saved_geometries_[n];
+  }
+
+protected:
+  virtual ~MultiGeometryWidget () {}
+
+private:
+  // Override this operation to implement any layout changes for the
+  // geometry specified by the argument 'n'.
+  virtual void change_layout (std::size_t n) = 0;
+
+  bool event (QEvent * e) override
+  {
+    auto ret = Widget::event (e);
+    if (QEvent::LayoutRequest == e->type ()
+        && desired_geometry_.size ())
+      {
+        // Restore the new desired geometry and flag that we have done
+        // so by clearing the desired_geometry_ member variable.
+        QByteArray geometry;
+        std::swap (geometry, desired_geometry_);
+        Widget::restoreGeometry (geometry);
+      }
+    return ret;
+  }
+
+  std::size_t current_geometry_;
+  std::array<QByteArray, N> saved_geometries_;
+  QByteArray desired_geometry_;
+};
+
+#endif