Implementing the MIDlet main class

ImageViewerMIDlet class

This is the main class of the MIDlet. It controls the display and handles the transitions between the different screens.

On the startApp call, ImageViewerMIDlet checks that the FileConnection API is supported by the device. If the API is not supported, ImageViewerMIDlet informs the user accordingly. If the API is supported, ImageViewerMIDlet creates a FileSelector and assigns it to the Display.

The requestInput and input methods are used to show the InputScreen and indicate the input result, respectively. The displayImage method is used to show the ImageCanvas displaying the selected image.

To create this class:

1. Create the ImageViewerMIDlet class file.

2. Import the required packages.

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

3. Implement the ImageViewerMIDlet class.

   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("/logo1.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
               if (!isAPIAvailable) {
                   String text = getAppProperty("MIDlet-Name") + "\n" +
                       getAppProperty("MIDlet-Vendor") +
                       "\nFile Connection API is not available";
                   Alert splashScreen = new Alert(null,
                           text,
                           logo,
                           AlertType.INFO);
                   Display.getDisplay(this).setCurrent(splashScreen);
               } else {
                   Display.getDisplay(this).setCurrent(fileSelector);
                   fileSelector.initialize();
               }
           } 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 cancelInput() {
           Display.getDisplay(this).setCurrent(fileSelector);
       }
   
       void input(String input) {
           fileSelector.inputReceived(input, operationCode);
           Display.getDisplay(this).setCurrent(fileSelector);
       }
   
       void displayImage(String imageName) {
           if(imageCanvas.displayImage(imageName) == true)
           {
               Display.getDisplay(this).setCurrent(imageCanvas);
           }
       }
   
       void displayFileBrowser() {
           Display.getDisplay(this).setCurrent(fileSelector);
       }
   
       void showError(String errMsg) {
           ErrorScreen.showError(errMsg, fileSelector);
       }
   
       void showError(Exception e) {
           ErrorScreen.showError(e.getMessage(), fileSelector);
       }
   
       void showMsg(String text) {
           Alert infoScreen = new Alert(null,
                   text,
                   logo,
                   AlertType.INFO);
           infoScreen.setTimeout(3000);
           Display.getDisplay(this).setCurrent(infoScreen, fileSelector);
       }
   
       Image getLogo() {
           return logo;
       }
   
       void requestInput(String text, String label, int operationCode) {
           inputScreen.setQuestion(text, label);
           this.operationCode = operationCode;
           Display.getDisplay(this).setCurrent(inputScreen);
       }
   
   
       // 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;
       }
   }

Now that you have implemented the MIDlet main class, implement the MIDlet functionality.