Java Reference
In-Depth Information
7.7.3 Double Buffering
As we've already seen, double buffering is supported by using the
lock()
and
unlock()
methods of the
Graphics
class. The Symbian
OS implementation of the MIDP
Canvas
class is double buffered by
default, or you use an offscreen image context to create your own double
buffer. This is not a major problem and changing your code base to deal
with it should be fairly easy.
7.7.4 Dialogs
DoJa uses the
Dialog
class in place of MIDP's
Alert
class. A
Dialog
is a fixed-function, very simple modal dialog and the following MIDP
functionality is not available:
•
automatic re-direction to a specified
Displayable
when the dialog
is dismissed
•
playing an appropriate (and device dependent) alert sound on display
•
using your own images - DoJa dialogs do not have any images
•
adding your own command buttons and listeners
•
timeouts - all dialogs are modal
•
activity indicators.
All you can do is simplify your alert management code to address this.
Applications that rely on post-dismissal re-directions are likely to require
the most re-engineering.
7.7.5 Softkeys
DoJa allows any screen to specify up to two softkeys and there is no
equivalent of the
Command
class, therefore there is no support for menus.
Depending on your application, this may require a careful re-design of
your application's navigation flows.
7.7.6 Text Positioning
The anchor point concept used extensively in MIDP is not used in DoJa.
When drawing text on a graphics context at a specified point, that point
is always relative to the left edge of the text and its baseline. Working
around this is a simple exercise in mathematics.
