Question

Hi guys i am trying an sample where i have a button which downloads an image and then it need to render on screen. I am using the following code to get it done. Don’t know somewhere i am going real wrong. it throws me illegal Exception. can anyone please look at my code and provide me some help.

import java.io.IOException;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import net.rim.device.api.system.Application;
import net.rim.device.api.system.Bitmap;
import net.rim.device.api.ui.Field;
import net.rim.device.api.ui.FieldChangeListener;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.component.BitmapField;
import net.rim.device.api.ui.component.ButtonField;
import net.rim.device.api.ui.container.MainScreen;


public class GoogleChart extends MainScreen implements FieldChangeListener{

    ButtonField btn = new ButtonField("Download");

    GoogleChart activeScreen = null;

    public GoogleChart() {
        setTitle("Download image"); 

        btn.setChangeListener(this);
        add(btn);

        this.activeScreen = (GoogleChart)UiApplication.getUiApplication().getActiveScreen();
    }

    public void fieldChanged(Field field, int context) {
        if(field == btn){
            updateUI();
        }
    }

    private void updateUI(){
        synchronized (Application.getEventLock()) {
            activeScreen.add(new BitmapField(downloadImage()));
            activeScreen.invalidate();
        }   
    }
    public Bitmap downloadImage() {
        byte[] dataArray;
        InputStream input;

        StringBuffer url = new StringBuffer("IMAGE URL"); 

        HttpConnection httpConn = null;
        Bitmap googleImage = null;
        try {
            httpConn = (HttpConnection) Connector.open(url.toString());

            input = httpConn.openInputStream();

            dataArray = net.rim.device.api.io.IOUtilities.streamToBytes(input);

            googleImage = Bitmap.createBitmapFromBytes(dataArray, 0, -1, 1);

        } catch (IOException e) {
            e.printStackTrace();
        }
            return googleImage;
    }
}

Note: Image download works fine. even i have tested with other sample.

As per Dan suggestion i have changed the following code and separated the downloading logic into another thread.

class Download extends Thread{
    Bitmap googleImage = null;

    private void updateUI(){
        synchronized (Application.getEventLock()) {
            if(googleImage != null){                
            activeScreen.add(new BitmapField(googleImage));
            activeScreen.invalidate();
            }
        }   
    }

    public void run() {
        googleImage = downloadImage();
        updateUI();

    }

    public Bitmap downloadImage() {
        byte[] dataArray;
        InputStream input;

        StringBuffer url = new StringBuffer("http://"); 

        HttpConnection httpConn = null;
        Bitmap googleImage = null;
        try {
            httpConn = (HttpConnection) Connector.open(url.toString());

            input = httpConn.openInputStream();

            dataArray = net.rim.device.api.io.IOUtilities.streamToBytes(input);

            googleImage = Bitmap.createBitmapFromBytes(dataArray, 0, -1, 1);

        } catch (IOException e) {
            e.printStackTrace();
        }
            return googleImage;
    }
}

and calling the thread like this

public void fieldChanged(Field field, int context) {
        if(field == btn){
            new Download().start();
        }
    }

Answer 1

What exception exactly do you get (does it have any message?)? At what step/line? As a possible case you may get an illegal exception if your Bitmap is too big to create a BitmapField instance. What dimensions (width x heigh) has your Bitmap? In my experience starting from ~1.5 Mpx it becomes impossible to create BitmapField (an exact limit depends on device model/OS level).

UPDATE:

OK, then to figure out what is going on could you try the following approach?

private void updateUI() {
    UiApplication.getUiApplication().invokeLater(new Runnable() {
        public void run() {
            if (googleImage == null) {
                Dialog.alert("googleImage is null");
            } else {
                Dialog.alert("googleImage is not null");
                try {
                    BitmapField b = new BitmapField(googleImage);
                    Dialog.alert("BitmapField has been created OK");
                    activeScreen.add(b);
                    Dialog.alert("BitmapField has been added OK");
                    // no need to invalidate, since adding a new Field forces
                    // the screen to be repainted
                } catch (Exception e) {
                    Dialog.alert("Got error: " + e);
                }
            }
        }
    });
}

What messages do you see? If you get “BitmapField has been added OK” then just remove all alerts (just leave the only in the catch section – just in case) and it should work Ok.