[lanfong]

Hi all,


Here's the situation I have.


I have two screens.
[A] is a built-in MainScreen.
[b] is a custom screen that I extends MainScreen with my custom paint.

[A] is my main screen of my app.

I have a menu item that goes to screen [b] called "Detail Screen"

I use pushModalScreen(new BScreen()) to display screen [b]


When I want to go back to screen [A], I hit the "ESC" key and uiApplication
then popScreen(this) ..(the "this" keyword in java) and pushScreen([A])

scr[b] holds an instance of scr[A] so I would be able to push [A] back...


ok then here it comes my problem
If I go from A to B - B to A many many times,the code that executes will be like calling
pushModalScreen(new BScreen())
pushModalScreen(new BScreen())
pushModalScreen(new BScreen())
pushModalScreen(new BScreen())
pushModalScreen(new BScreen())
pushModalScreen(new BScreen())
pushModalScreen(new BScreen())
pushModalScreen(new BScreen())
pushModalScreen(new BScreen())

is it what people usually do when developing in BlackBerry????




What would be the best practice when developing multiple screens???
If anyone has developed multiple screens app, I will be happy to know
what your ideas.

[joeisom]

I just jumped on the forums to ask the same question!

If I am correct, whenever you "pop" a screen, the object is no longer used, so the JVM will preform garbage collection on it (eventually).

I have tried something similar to the following, but not sure how "thread-safe" it is. (I'm just learning java, so I'm not an expert in thread-safety yet)

PHP Code:

import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.container.MainScreen;

public class MyScreen extends MainScreen 
{    
    private static MyScreen _singleInstance = null;

    public MyScreen() 
    {
        super();
        
        // Add Components / Fields Here!
        
        synchronized(this)
        {
            _singleInstance = this;
        }
    }

    public static MyScreen getMyScreen()
    {
        if(_singleInstance == null)
        {
            _singleInstance = new MyScreen();
        }
        return _singleInstance;
    }
} 


Then replace:

PHP Code:

UiApplication.getUiApplication().pushScreen(new MyScreen()); 


with:

PHP Code:

UiApplication.getUiApplication().pushScreen(getMyScreen()); 


Doing this ensures that you are not constantly creating / destroying screens that do not change.

So, I hope I kind-of answered your question. The JVM takes care of garbage collection on the "pop"ed screens. But you are taking a performance hit by constantly creating and destroying something that may not change frequently.

Anyone have other tips on this?