Implementing the main MIDlet

ImageViewerMIDlet class

This is the MIDlet class implementation of the example. It has control over the Display and makes transitions between screens. On the first startApp call it will check that the FileConnection API is effectively present, otherwise it will inform the user. If it is available, it will create a FileSelector and assign it to the display.

The requestInput() and input()methods are used to show the InputScreen and to indicate the result of it respectively. The displayImage() method is invoked to show ImageCanvas displaying a particular image.

To create this class:

1. Create the ImageViewerMIDlet class file.

2. Import the required classes.

   import javax.microedition.lcdui.*;
   import javax.microedition.midlet.*;

3. Implement the class.

   // Main class which inits the MIDlet and creates the screens
   public class ImageViewerMIDlet
     extends MIDlet
   {
     private final Image logo;
     private final ImageCanvas imageCanvas;
     private FileSelector fileSelector;
     private final InputScreen inputScreen;
     private int operationCode = -1;
   
     public ImageViewerMIDlet()
     {
       // init basic parameters
       logo = makeImage("/logo.png");
       ErrorScreen.init(logo, Display.getDisplay(this));
       imageCanvas = new ImageCanvas(this);
       fileSelector = new FileSelector(this);
       inputScreen = new InputScreen(this);
     }
     public void startApp()
     {
       Displayable current = Display.getDisplay(this).getCurrent();
       if (current == null)
       {
         // Checks whether the API is available
         boolean isAPIAvailable = System.getProperty(
           "microedition.io.file.FileConnection.version") != null;
         // shows splash screen
         String text = getAppProperty("MIDlet-Name")
           + "\n"
           + getAppProperty("MIDlet-Vendor");
         if (!isAPIAvailable)
         {
           text += "\nFile Connection API is not available";
         }
         Alert splashScreen = new Alert(null,
           text,
           logo,
           AlertType.INFO);
         if (isAPIAvailable)
         {
           splashScreen.setTimeout(30);
           Display.getDisplay(this).setCurrent(splashScreen,
             fileSelector);
         }
         else
         {
           Display.getDisplay(this).setCurrent(splashScreen);
         }
       }
       else
       {
         Display.getDisplay(this).setCurrent(current);
       }
     }
     public void pauseApp()
     {
     }
     public void destroyApp(boolean unconditional)
     {
       // stop the commands queue thread
       fileSelector.stop();
       notifyDestroyed();
     }
     void fileSelectorExit()
     {
       destroyApp(false);
     }
     void requestInput(String text, String label, int operationCode)
     {
       inputScreen.setQuestion(text, label);
       this.operationCode = operationCode;
       Display.getDisplay(this).setCurrent(inputScreen);
     }
     void cancelInput()
     {
       Display.getDisplay(this).setCurrent(fileSelector);
     }
     void input(String input)
     {
       fileSelector.inputReceived(input, operationCode);
       Display.getDisplay(this).setCurrent(fileSelector);
     }
     void displayImage(String imageName)
     {
       imageCanvas.displayImage(imageName);
       Display.getDisplay(this).setCurrent(imageCanvas);
     }
     void displayFileBrowser()
     {
       Display.getDisplay(this).setCurrent(fileSelector);
     }
     void showError(Exception e)
     {
       ErrorScreen.showError(e.getMessage(), fileSelector);
     }
     void showMsg(String text)
     {
       Alert infoScreen = new Alert("Image Viewer",
         text,
         logo,
         AlertType.INFO);
       infoScreen.setTimeout(3000);
       Display.getDisplay(this).setCurrent(infoScreen, fileSelector);
     }
     // loads a given image by name
     static Image makeImage(String filename)
     {
       Image image = null;
       try
       {
         image = Image.createImage(filename);
       }
       catch (Exception e)
       {
         // use a null image instead
       }
       return image;
     }
   }