From Forum Nokia Wiki

Application Design Tips

• The most important design tip for Symbian OS is to separate out your engine and UI code into different modules. Symbian OS itself is designed in this way and it aids porting between different UI systems. All non-UI related code should be put into a separate engine .DLL file. Your Application UI can then link to this .DLL for access to engine functionality.

By coding in this way, you ease the porting burden for new UI platforms. Pure engine code often runs unaltered on any UI platform. This means that all you have to port and optimize for a new UI is your own, separate UI layer.

• Always design with support for localization in mind. Never hardcode strings or literals into your source files – always use the resource file mechanism Symbian OS provides to store strings.

• Take care to stick to using APIs which are documented and supported for given SDK and Symbian OS releases. The use of unsupported or deprecated APIs can lead to future problems for your application – for example, Symbian reserves the right to change or remove APIs which are not intended to be used by external developers.