Commands sometimes don't work - java-me

Question

There is a Canvas which has two Commands. The problem is that when the canvas is first opened then the commands work , but when I open it for the second time then the command doesn't work! Here is the code:
package view;
import java.io.IOException;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.file.FileConnection;
import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;
import javax.microedition.lcdui.StringItem;
public class DetailPhotoClient extends Canvas implements CommandListener {
private Command delete, back;
private GaleriePhotos backForm;
private FileConnection fcFile;
private Image sourceImage;
private InputStream is;
private boolean ok,oom, io;
public DetailPhotoClient(GaleriePhotos prevForm, String absolutePathphotoName)
{
super();
back = new Command("Retour", Command.SCREEN, 1);
addCommand(back);
delete = new Command("Supprimer", Command.SCREEN, 2);
addCommand(delete);
setCommandListener(this);
backForm = prevForm;
ok = true;
oom = false;
io = false;
try {
fcFile = (FileConnection) Connector.open(absolutePathphotoName, Connector.READ);
is = fcFile.openInputStream();
sourceImage = Image.createImage(is);
is.close();
fcFile.close();
} catch (IOException ex) {
handleException();
} catch (OutOfMemoryError oome) {
handleOOM();
}
}
private void handleException() {
ok = false;
io = true;
repaint();
}
private void handleOOM() {
ok = false;
oom = true;
repaint();
}
protected void paint(Graphics g) {
StringItem chp;
int chpW;
int x, y = getHeight()/2;
g.fillRect(0, 0, getWidth(), getHeight());
if (ok)
g.drawImage(sourceImage, 0, 0, Graphics.TOP | Graphics.LEFT);
if (io)
{
chp = new StringItem(null,"Erreur média et/ou d'entrée-sortie !");
chpW = chp.getPreferredWidth();
x = ( getWidth() - chpW ) / 2 ;
g.setColor(16711422);
if (x<0)
g.drawString("Erreur média et/ou d'entrée-sortie !", 0, y, Graphics.TOP | Graphics.LEFT);
else
g.drawString("Erreur média et/ou d'entrée-sortie !", x, y, Graphics.TOP | Graphics.LEFT);
}
if (oom)
{
chp = new StringItem(null,"Mémoire insuffisante !");
chpW = chp.getPreferredWidth();
x = ( getWidth() - chpW ) / 2 ;
g.setColor(16711422);
if (x<0)
g.drawString("Mémoire insuffisante !", 0, y, Graphics.TOP | Graphics.LEFT);
else
g.drawString("Mémoire insuffisante !", x, y, Graphics.TOP | Graphics.LEFT);
}
}
public void commandAction(Command c, Displayable d) {
if (c == back)
backForm.showBack();
else
{
backForm.showBack();
backForm.deletePhoto();
}
}
}
So why doesn't the Command work sometimes? Tested the app with an Alcatel OT-806D phone

Answer 1

Well your code is widely exposed to threats related to CommandListener to start with. Look, any piece of code "outside" your class can make your commands irresponsive:
void makeItDeaf(DetailPhotoClient detailPhotoClient) {
detailPhotoClient.setCommandListener(null);
// voila! your commands will be still visible but
// wouldn't respond anymore
}
To make sure that you don't accidentally break the command listener like above, "hide" it about as follows:
//...
public class DetailPhotoClient extends Canvas { // no "implements" here
private Command delete, back;
private GaleriePhotos backForm;
private FileConnection fcFile;
private Image sourceImage;
private InputStream is;
private boolean ok,oom, io;
public DetailPhotoClient(GaleriePhotos prevForm,
String absolutePathphotoName)
{
super();
back = new Command("Retour", Command.SCREEN, 1);
addCommand(back);
delete = new Command("Supprimer", Command.SCREEN, 2);
addCommand(delete);
backForm = prevForm;
setCommandListener(new CommandListener() {
public void commandAction(Command c, Displayable d) {
if (backForm == null) {
System.out.println("backForm is null: ignore command");
return;
}
if (c == back) {
System.out.println("back command");
backForm.showBack();
} else {
System.out.println("delete command");
backForm.showBack();
backForm.deletePhoto();
}
}
});
ok = true;
oom = false;
//...
}
//...
}