Implementing the MIDlet main class

The ImageViewerMIDlet class is the MIDlet main class. When the MIDlet is launched, the ImageViewerMIDlet class is loaded first.

The ImageViewerMIDlet class handles the following tasks:

• Common startup events such as setting the default Display

• Displaying the splash screen as the MIDlet launches

• Common pauseApp and destroyApp tasks

• Transitions between different MIDlet views, such as launching the FileSelector

To implement the ImageViewerMIDlet class:

1. Create the ImageViewerMIDlet.java class file.

2. Import the required classes.

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

3. Implement the ImageViewerMIDlet class functionality.

   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 an operations queue for more effective user action handling.