Chapter 1

destroyed frequently in application use, so these optimizations make a significant
difference.
� Reduced overheads: Lodgers also reduce the overheads associated with complex
entities such as a dialog because controls are much more compact in memory than
windows.
� Less processing : Lodgers have less demanding processing requirements. Windows
may move, change z order, and overlap arbitrarily. Lodgers at peer level on the same
window never intersect and they only occupy a subregion of their owning window or
control. This makes the logic for detecting intersections much easier than that required
for the arbitrarily complex regions managed by the window server.
When you need a window
All these factors improve the system efficiency of Symbian OS, compared to a scenario with
no lodger controls. In order to take advantage of these features, most controls should be
coded as lodgers, but there are a few circumstances in which you need a window:
� When there is no window to lodge in – this is the case for the application view.
� When you need shadows, as described later in this chapter. Shadows are used by
dialogs, popup menus, popup list-boxes, menu panes, and the menu bar.
� When you need a backed-up window – we'll come back to these later.
� When you need to overlap peer controls in an arbitrary way – not according to lodger
controls' stricter nesting rules.
� When you need the backup-behind property (see below), which is used by dialogs and
menu panes to hold a bitmap of the window behind them.
Being window-owning is a fairly fundamental property of a control. There isn't much point in
coding a control bimodally – that is, to be either a lodger or to be window-owning. Decide
which it should be and commit to it.
On the other hand, only small parts of your control's code will be affected by the decision.
So, if you find out later that (for instance) your control that was previously a stand-alone app
view now has a window to lodge in, then you should be able to modify your control quite
easily.
For instance, in the drawing example in Chapter 15, the CExample-HelloControl class
adapts hellogui's CHelloGuiAppView to turn it into a lodger. The class declaration
changes from:
class CHelloGuiAppView : public CCoeControl
{
public:
static CHelloGuiAppView* NewL(const TRect& aRect);
~CHelloGuiAppView();
void ConstructL(const TRect& /*aRect*/);
private:
void Draw(const TRect& /* aRect */) const;
private:
HBufC* iHelloText;
};
to:
class CExampleHelloControl : public CCoeControl