Implementation of ImageViewer

The following UML diagram identifies the classes used in the Image Viewer example:

Figure 113: ImageViewerMIDlet class diagram

The ImageViewer example consists of the following classes:

• ImageViewerMIDlet

  This is the starting point of the application. It controls the display and handles the transitions between the different screens.

• FileSelector

  The class contains the bulk of the application. It contains the user interface and navigates the device's file system. It also contains support for file-oriented operations such as delete, rename, and directory creation. FileSelector will check whether the fileconn.dir.photos system property is available and will start navigating the file system on that directory if available. Otherwise, it will display a list of all the available roots.

• ImageCanvas

  The class displays a selected image on the screen and upon detecting a key being pressed returns to the FileSelector.

• OperationsQueue

  One important consideration when designing the Image Viewer MIDlet is that I/O operations are to be executed in a separate thread. The OperationsQueue class accomplishes this by executing commands serially in a separate thread.

• Operation

  The class defines the Operation interface used by OperationsQueue.

• InputScreen

  The class InputScreen is a simple form used to prompt the user to enter some text. This is used when creating a new directory or when renaming a file.

• ErrorScreen

  ErrorScreen is a simple class used for reporting errors to the end user.

The GUI consists of a simple file browser displaying the current directories and allowing navigation up and down the directory tree. The figures below show two screenshots of the file browser.

Figure 114: File Browser user interface in a Nokia device and a Nokia Communicator

Once an image is selected, it is displayed on a simple canvas with a black background as shown in the figure below.

Figure 115: ImageViewer user interface