Multiple screens can be open on a BlackBerry® device at one time, but users can view only one screen at a time. When multiple screens are open, they are organized in a stack. The screen at the top of the stack is the active screen. When an application displays a screen, the BlackBerry® Java® Virtual Machine pushes it to the top of the stack. When a screen closes, the BlackBerry Java Virtual Machine deletes the screen from the top of the stack and displays the next screen on the stack. The application redraws the screen as necessary.
Users can perform the following common actions on screens:
Best practice: Designing application screens
- Delete your application screen from the stack when users close a screen. If you use standard components, the BlackBerry® device automatically deletes screens from the stack.
- Repaint the screen judiciously. Your BlackBerry device application should not perform unnecessary screen repaints.
- Use a limited number of nested layouts. The more nested layouts that you use to build your screen, the longer it takes for the BlackBerry device to render the screen.
- Prompt users with a dialog box to save any unsaved data before closing a screen.
- Avoid hardcoding color values. The color values that you choose might not work with the theme that users have selected.
Guidelines for layout
- Use a vertical layout for your application screens.
- Consider arranging the UI components on application screens using the BlackBerry API layout managers. For more information about arranging UI components, see the API reference guide for the BlackBerry® Java® SDK and the BlackBerry Java Application UI and Navigation Development Guide.
- On BlackBerry devices with a touch screen, verify that the screens display correctly in both portrait and landscape view.
- Display the most important information at the top of the screen. For example, for contact information, display the name first, followed by the email address and phone numbers. Display a field such as the Notes field last.
- Limit the number of components that appear on the screen at one time.
- Use line separators on a screen to separate components or to indicate a group of components.
- Consider localization requirements as early in the design process as possible. Localization can affect the layout of screens.