(J2ME) get the reference of the MIDlet from some other class?

Question

I am trying to make a class that can set what is on the screen (Like set a Form to the Display, what ever.) outside the midlet (Main) class
So I thought I have to enter and change the Main's variable display, but I went to an error.

Here's the whole program:

//Main.java
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class Main extends MIDlet {

    public Other othr = new Other(this);
    public Display display = Display.getDisplay(this);
    public void startApp() {
        display.setCurrent(othr);
    }

    public void pauseApp() {
    }

    public void destroyApp(boolean unconditional) {
    }
}

//Other.java
import javax.microedition.lcdui.*;
public class Other extends Canvas{

    Form a = new Form("a");
    public TextEdit(Main mc){
        //HERE IT IS!
        mc.display.getDisplay(mc).setCurrent(a);
        //If I comment out the above, I get no error.

    }
    protected void paint(Graphics g) {
         //Nothing yet
    }

}

And I always get the error "The application has unexpectedly quit".

I also tried to replace mc.display.getDisplay(mc).setCurrent(a); with Display.getDisplay(mc).setCurrent(a);, error is not showed then, but Form a isn't displayed at all.

It's likely to be a stupid mistake, but I'm lost

What can I do?

Answer 1

It's a small mistake in your code. Make changes in your code like following.

//Main.java
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class Main extends MIDlet {

    public Other othr ;
    public Display display ;
    public void startApp() {
         display= Display.getDisplay(this);
        othr=new Other(this);
        display.setCurrent(othr);
    }

    public void pauseApp() {
    }

    public void destroyApp(boolean unconditional) {
    }
}

and check your Other look like this, make sure what you want Form or Canvas both are different.

For Form your code like this

//Other.java
import javax.microedition.lcdui.*;
public class Other {

    Form a ;
    public Other(Main mc){
        //HERE IT IS!
       a=new Form("a");
        Display.getDisplay(mc).setCurrent(a);
        //If I comment out the above, I get no error.

    }

}

For Canvas check this one

/Other.java
import javax.microedition.lcdui.*;
public class Other extends Canvas{

     public Other(Main mc){
        //HERE IT IS!
        Display.getDisplay(mc).setCurrent(this);
        //If I comment out the above, I get no error.

    }
    protected void paint(Graphics g) {
         //Nothing yet
    }

}

This will help you, Note:: Check difference between Canvas & Forms.

Answer 2

Replace

 public Other othr = new Other(this);
 public Display display = Display.getDisplay(this);

With

public Other othr;
public Display display;

public Main()
{
  othr = new Other(this);
  display = Display.getDisplay(this)
}