[SWT] How to enable and disable windows correctly, if using dialogs?

Hi,

I am programming a configuration gui for a hardware simulator. There I
wrote some gui elements, which enable the user to set up some
parameters used by the simulator.

For example it is possible to enter values in textfields. I do a check,
if the entered value even is an int, and if not, I create a short error
message. For example like this:

        textwidth.addModifyListener(new ModifyListener() {
            public void modifyText(ModifyEvent e) {
                try {
                    width = Integer.parseInt(textwidth.getText());
                } catch (NumberFormatException nfe){
                    if (!textwidth.getText().equals("")) {
                        width = 0;
                        ErrorHandling error = new ErrorHandling(
                            "Please enter numbers only!\r\nWidth is
reset to 0.",
                            selscomposite.getShell());
                        textwidth.setText("0");
                    }
                }
                //modify the scale so it represents the entered value
                scalewidth.setSelection(scalewidth.getMaximum() - width
+ scalewidth.getMinimum());
            }
        });

textwidth is the textfield, representing the value chosen through a
scale and enabling the user to enter a value manually, and the
scale-representation is updated if done so.

ErrorHandling is the class I use throughout the project to display
small error messages. It looks like this:

public class ErrorHandling {

    Shell error;
    Shell parentshell;

    public ErrorHandling(String errormessage, Shell shell) {

        //shell displaying the errormessage
        error = new Shell(SWT.TITLE | SWT.BORDER);
        error.setText("User input error");
        //the layout for the error shell
        FillLayout filllayout = new FillLayout(SWT.VERTICAL);
        filllayout.marginHeight = 5;
        filllayout.marginWidth = 5;
        filllayout.spacing = 3;

        error.setLayout(filllayout);
        //disable the parent shell
        parentshell = shell;
        parentshell.setEnabled(false);

        //set the errormessage
        CLabel errorlabelmessage = new CLabel(error, SWT.CENTER |
SWT.SHADOW_IN);
        errorlabelmessage.setText(errormessage);

        //a button to close the errormessage
        Button errorreceived = new Button(error, SWT.PUSH |
SWT.CENTER);
        errorreceived.setText("Ok, i got it!");
        errorreceived.addSelectionListener(new SelectionAdapter() {
            public void widgetSelected(SelectionEvent e) {
                parentshell.setEnabled(true);
                error.close();
            }
        });

        //create the errorshell
        error.setActive();
        error.pack();
        error.open();
    }
}

parentshell is needed, so I can disable the shell, in which the error
occured until the user hast closed the errormessage by using the "Ok, I
got it!"-button. I don't even know if this is good style, but it's all
I know to do so far. I need to have a new shell-variable (e.g.
parentshell), because otherwise I could not use it in the inner class
within the listener-context. This leads to the first question: Is there
no better way to handle this, but the new Object "parentshell"?

The second problem with this implementation is, that if I do not use
the SWT.BORDER and SWT.TITLE constants within the initialization of the
error-Shell-object, the small window displaying the error message looks
real crappy. The title and a window border is needed, but if I have
those, I also have a close-button on the upper right of the window.
Because a disabled the parent shell:

        parentshell = shell;
        parentshell.setEnabled(false);

I have to enable it, if the error message is closed. I am able to
enable it, if the user choses the button, but if the user closes the
window by the close-button of the window-manager, the parent-shell
never ever gets accessible, because there never came a command to
enable it again.

A last few words: I tried several constants in the creation of the
error-Shell-object, but most of them (like ON_TOP, or several modal
state specifiers) only have the effect, that the error-message has no
border and no title any more. I am using Linux and the X-Server, so I
don't know what the behaviour of these constants would be on other
window-architectures.

Now this was a whole lot of information, but ask me, if you want to
know something more specific. Any comments are welcome, even those,
telling me what I have done is totally crap and I should do it like
this or that.

Thank you in advance!

PS: Sorry for any errors and the bad english.