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Display Class Dispose method [message #659664]

Tue, 15 March 2011 05:38

Dharam

Messages: 18
Registered: December 2010

Junior Member

Hi!!
I have created RenameDialog class by subclassing Dialog class as shown below. (necessary only)

public class RenameDialog extends Dialog{
protected RenameDialog(Shell parentShell) {
super(parentShell);
setShellStyle(getShellStyle() | SWT.SHELL_TRIM);
}

protected void configureShell(Shell newShell)
{
super.configureShell(newShell);
newShell.setText("Rename Dialog");
newShell.setSize(500,150);
}

protected Control createDialogArea(Composite parent)
{}
}

When I am running this using code shown below, on closing of dialog, dialog disappears but disposing of display doesn't happen.

public class RenameDialogTest {

public static void main(String[] args) {
Display display=new Display();
Shell shell=new Shell(display,SWT.BORDER | SWT.TITLE);
RenameDialog dialog=new RenameDialog(shell);
if(dialog.open()==Window.OK)
System.out.println("OK");
while(!shell.isDisposed())
{
if(!display.readAndDispatch())
{
display.sleep();
}
}

display.dispose();
}

}

On above code if I remove, if(!display.readAndDispatch()){..}, it works fine. Could u please explain me the exact funda of this method?

Thanks

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Re: Display Class Dispose method [message #659734 is a reply to message #659664]

Tue, 15 March 2011 12:08

Thomas Schindl

Messages: 6651
Registered: July 2009

Senior Member

Your main shell is not disposed. The dialog is show in an extra shell
which is a child of the shell you passed in! You can prove this by
calling shell.open()

Tom

Am 15.03.11 06:38, schrieb Dharam:
> Hi!!
> I have created RenameDialog class by subclassing Dialog class as shown
> below. (necessary only)
>
> public class RenameDialog extends Dialog{
> protected RenameDialog(Shell parentShell) {
> super(parentShell);
> setShellStyle(getShellStyle() | SWT.SHELL_TRIM); }
>
> protected void configureShell(Shell newShell)
> {
> super.configureShell(newShell);
> newShell.setText("Rename Dialog");
> newShell.setSize(500,150);
> }
>
> protected Control createDialogArea(Composite parent)
> {}
> }
>
>
> When I am running this using code shown below, on closing of dialog,
> dialog disappears but disposing of display doesn't happen.
>
> public class RenameDialogTest {
>
> public static void main(String[] args) {
> Display display=new Display();
> Shell shell=new Shell(display,SWT.BORDER | SWT.TITLE);
> RenameDialog dialog=new RenameDialog(shell);
> if(dialog.open()==Window.OK)
> System.out.println("OK");
> while(!shell.isDisposed())
> {
> if(!display.readAndDispatch())
> {
> display.sleep();
> }
> }
>
> display.dispose();
> }
>
> }
>
>
> On above code if I remove, if(!display.readAndDispatch()){..}, it works
> fine. Could u please explain me the exact funda of this method?
>
> Thanks

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Re: Display Class Dispose method [message #659743 is a reply to message #659734]

Tue, 15 March 2011 13:11

Dharam

Messages: 18
Registered: December 2010

Junior Member

Thanks.

Yes I agree. But main shell has also been created using
new Shell(display).

So why on method call display.dispose() wouldn't deallocate all resources under "display"?

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Re: Display Class Dispose method [message #659749 is a reply to message #659743]

Tue, 15 March 2011 13:18

Thomas Schindl

Messages: 6651
Registered: July 2009

Senior Member

You are not getting there you stay in the loop because shell.isDiposed()
is always true and will always be true.

Tom

Am 15.03.11 14:11, schrieb Dharam:
> Thanks.
>
> Yes I agree. But main shell has also been created using
> new Shell(display).
>
> So why on method call display.dispose() wouldn't deallocate all
> resources under "display"?

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Re: Display Class Dispose method [message #659766 is a reply to message #659749]

Tue, 15 March 2011 14:32

Thomas Schindl

Messages: 6651
Registered: July 2009

Senior Member

Am 15.03.11 14:18, schrieb Tom Schindl:
> You are not getting there you stay in the loop because shell.isDiposed()
> is always true and will always be true.

Should read ! shell.isDisposed is always true

>
> Tom
>
> Am 15.03.11 14:11, schrieb Dharam:
>> Thanks.
>>
>> Yes I agree. But main shell has also been created using
>> new Shell(display).
>>
>> So why on method call display.dispose() wouldn't deallocate all
>> resources under "display"?
>

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Re: Display Class Dispose method [message #659909 is a reply to message #659766]

Wed, 16 March 2011 05:22

Dharam

Messages: 18
Registered: December 2010

Junior Member

Thanks.

Hmm you are saying that shell.isDisposed() would return always true in this case,but

->As long as the shell remains open, shell.isDisposed() would return false & it would make while loop condition true

-> This true will allow Display instance to call readAndDispatch() method to keep track of relevant user events in queue.

-> When 1 of this action involves closing of shell, it would make Display to come out of Sleep() & shell.isDisposed() to return true, so as to come out of while loop & call dispose() method.

If I am wrong anywhere, please guide me. Wht should I do in this case then?

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Re: Display Class Dispose method [message #659913 is a reply to message #659909]

Wed, 16 March 2011 06:18

Thomas Schindl

Messages: 6651
Registered: July 2009

Senior Member

As you see I corrected my self !shell.isDisposed() == true. If you close
the dialog *the shell of the Dialog is closed* but not the shell you
created in your main()-method.

Could you please add shell.open() before you do a dialog.open() then you
maybe understand what I'm telling you.

Tom

Am 16.03.11 06:22, schrieb Dharam:
> Thanks.
>
> Hmm you are saying that shell.isDisposed() would return always true in
> this case,but
>
> ->As long as the shell remains open, shell.isDisposed() would return
> false & it would make while loop condition true
>
> -> This true will allow Display instance to call readAndDispatch()
> method to keep track of relevant user events in queue.
> -> When 1 of this action involves closing of shell, it would make
> Display to come out of Sleep() & shell.isDisposed() to return true, so
> as to come out of while loop & call dispose() method.
>
> If I am wrong anywhere, please guide me. Wht should I do in this case then?

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