user interface - Blackberry - Application loading screen

Question

My application contains lots of images. so it takes some time to load the application. I want to show a loading screen whhile the application is being loaded. How is it possible ?

Answer 1

Here's an example app that skeletons what your looking to do. Basically, the initial screen you push is a loading screen. During the initial startup sequence you need to spin up a new thread, do your loading stuff and then use invokeLater to 1) make sure your in the event dispatcher and 2) to push a new screen -- or in the case of this example a dialog -- to the screen to have the user progress away from the loading screen.

Here's the code:

import net.rim.device.api.ui.Field;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.container.MainScreen;
import net.rim.device.api.ui.component.Dialog;
import net.rim.device.api.ui.component.LabelField;

/**
 * Just a test app.
 */
public class TestAppMain extends UiApplication 
{
    /**
     * Default Constructor.
     */
    private TestAppMain() {                
        pushScreen(new AppScreen(this));        
    }

    /**
     * App entry point.
     * @param args Arguments.
     */
    public static void main(String[] args) {
        TestAppMain app = new TestAppMain();                       
        app.enterEventDispatcher();
    }

    /**
     * Main application screen.
     */
    private static class AppScreen extends MainScreen 
    {
        UiApplication _app;

        /**
         * Default constructor.
         */
        public AppScreen(UiApplication app) {
            // Note: This screen just says "Loading...", but you could
            // add a loading animation.
            _app = app;
            LabelField title = new LabelField("App Name",
                    LabelField.ELLIPSIS | LabelField.USE_ALL_WIDTH);
            setTitle(title);

            LabelField loading = new LabelField("Loading...",
                    LabelField.ELLIPSIS | LabelField.USE_ALL_WIDTH);

            add(loading);

            // Queue up the loading process.
            startLoading();
        }               

        /**
         * Create the loading thread. Make sure to invoke later as you will
         * need to push a screen or show a dialog after the loading is complete, eventhough
         * you are creating the thread before the app is in the event dispatcher.
         */
        public void startLoading() { 
            Thread loadThread = new Thread() {
                public void run() {
                    // Make sure to invokeLater to avoid problems with the event thread.
                    try{ 
                        // Simulate loading time
                        Thread.sleep(5000);
                    } catch(java.lang.InterruptedException e){}

                    // TODO - Add loading logic here.

                    _app.invokeLater( new Runnable() {                
                        public void run() {                    
                            // This represents the next step after loading. This just shows 
                            // a dialog, but you could push the applications main menu screen.
                            Dialog.alert("Load Complete");
                        }
                    });
                }
            };
            loadThread.start();
        }
    }
}