You can open a new window by creating a new Window object and adding it to the main window with addWindow() method of the Application class.

mywindow = new Window("My Window");
mainwindow.addWindow(mywindow);

You close the window in a similar fashion, by calling the removeWindow() of the Application class:

myapplication.removeWindow (mywindow);

The user can, by default, close a child window by clicking the close button in the upper-right corner of the window. You can disable the button by setting the window as read-only with setReadOnly(true). Notice that you could disable the button also by making it invisible in CSS with a "display: none" formatting. The problem with such a cosmetic disabling is that a malicious user might re-enable the button and close the window, which might cause problems and possibly be a security hole. Setting the window as read-only not only disables the close button on the client side, but also prevents processing the close event on the server side.

The following example demonstrates the use of a child window in an application. The example manages the window using a custom component that contains a button for opening and closing the window.

/** Component contains a button that allows opening a window. */
public class WindowOpener extends CustomComponent
                          implements Window.CloseListener {
    Window mainwindow;  // Reference to main window
    Window mywindow;    // The window to be opened
    Button openbutton;  // Button for opening the window
    Button closebutton; // A button in the window
    Label  explanation; // A descriptive text

    public WindowOpener(String label, Window main) {
        mainwindow = main;

        /* The component consists of a button that opens the window. */
        final OrderedLayout layout = new OrderedLayout();
        
        openbutton = new Button("Open Window", this, "openButtonClick");
        explanation = new Label("Explanation");
        layout.addComponent(openbutton);
        layout.addComponent(explanation);
        
        setCompositionRoot(layout);
    }

    /** Handle the clicks for the two buttons. */
    public void openButtonClick(Button.ClickEvent event) {
        /* Create a new window. */
        mywindow = new Window("My Dialog");
        mywindow.setPositionX(200);
        mywindow.setPositionY(100);

        /* Add the window inside the main window. */
        mainwindow.addWindow(mywindow);

        /* Listen for close events for the window. */
        mywindow.addListener(this);

        /* Add components in the window. */
        mywindow.addComponent(new Label("A text label in the window."));
        closebutton = new Button("Close", this, "closeButtonClick");
        mywindow.addComponent(closebutton);

        /* Allow opening only one window at a time. */
        openbutton.setEnabled(false);

        explanation.setValue("Window opened");
    }

    /** Handle Close button click and close the window. */
    public void closeButtonClick(Button.ClickEvent event) {
        /* Windows are managed by the application object. */
        mainwindow.removeWindow(mywindow);

        /* Return to initial state. */
        openbutton.setEnabled(true);

        explanation.setValue("Closed with button");
    }

    /** In case the window is closed otherwise. */
    public void windowClose(CloseEvent e) {
        /* Return to initial state. */
        openbutton.setEnabled(true);

        explanation.setValue("Closed with window controls");
    }
}

You can use the above custom component in the application class with:

    public void init() { 
        Window main = new Window("The Main Window"); 
        setMainWindow(main);

        addComponent(new WindowOpener("Window Opener", main));
    }

The example implements a custom component that inherits the CustomComponent class. It consists of a Button that it uses to open a window and a Label to describe the state of the window. When the window is open, the button is disabled. When the window is closed, the button is enabled again.

When added to an application, the screen will look as illustrated in the following screenshot:

When created, a window will have a default size and position. You can specify the size of a window with setHeight() and setWidth() methods. You can set the position of the window with setPositionX() and setPositionY() methods.

/* Create a new window. */
mywindow = new Window("My Dialog");

/* Set window size. */
mywindow.setHeight(200);
mywindow.setWidth(400);

/* Set window position. */
mywindow.setPositionX(200);
mywindow.setPositionY(50);

Notice that the size of the main window is unknown and the getHeight and getWidth methods will return -1.

A modal window is a child window that has to be closed by the user before the use of the parent window can continue. Dialog windows are typically modal. The advantage of modal windows is the simplification of user interaction, which may contribute to the clarity of the user interface. Modal windows are also easy to use from a development perspective, because as user interaction is isolated to them, changes in application state are more limited while the modal window is open. The disadvantage of modal windows is that they can restrict workflow too much.

Depending on theme settings, the parent window may be grayed while the modal window is open.

The demo application of IT Mill Toolkit includes an example of using modal windows. Figure 3.2, “Screenshot of the Modal Window Demo Application” above is from the demo application. The example includes the source code.