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Sub-windows are floating panels within a native browser window. Unlike native browser windows, sub-windows are managed by the client-side runtime of Vaadin using HTML features. Vaadin allows opening, closing, resizing, maximizing and restoring sub-windows, as well as scrolling the window content.

subwindow basic
A Sub-Window

Sub-windows are typically used for Dialog Windows and Multiple Document Interface applications. Sub-windows are by default not modal; you can set them modal as described in Modal Sub-Windows.

Opening and Closing Sub-Windows

You can open a new sub-window by creating a new Window object and adding it to the UI with addWindow(), typically in some event listener. A sub-window needs a content component, which is typically a layout.

In the following, we display a sub-window immediately when a UI opens:

public static class SubWindowUI extends UI {
    protected void init(VaadinRequest request) {
        // Some other UI content
        setContent(new Label("Here's my UI"));

        // Create a sub-window and set the content
        Window subWindow = new Window("Sub-window");
        VerticalLayout subContent = new VerticalLayout();

        // Put some components in it
        subContent.addComponent(new Label("Meatball sub"));
        subContent.addComponent(new Button("Awlright"));

        // Center it in the browser window;

        // Open it in the UI

The result was shown in A Sub-Window. Sub-windows by default have undefined size in both dimensions, so they will shrink to fit the content.

The user can close a sub-window by clicking the close button in the upper-right corner of the window. The button is controlled by the closable property, so you can disable it with setClosable(false). You can also use keyboard shortcuts for closing a sub-window. You can manage the shortcuts with the addCloseShortcut(), removeCloseShortcut(), removeAllCloseShortcuts(), hasCloseShortcut(), and getCloseShortcuts() methods.

You close a sub-window also programmatically by calling the close() for the sub-window, typically in a click listener for an OK or Cancel button. You can also call removeWindow() for the current UI.

Sub-Window Management

Usually, you would extend the Window class for your specific sub-window as follows:

// Define a sub-window by inheritance
class MySub extends Window {
    public MySub() {
        super("Subs on Sale"); // Set window caption

        // Disable the close button

        setContent(new Button("Close me", event -> close()));

You could open the window as follows:

// Some UI logic to open the sub-window
final Button open = new Button("Open Sub-Window");
open.addClickListener(event -> {
    MySub sub = new MySub();

    // Add it to the root component

Window Positioning

When created, a sub-window will have an undefined 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 sub-window
mywindow = new Window("My Dialog");

// Set window size.

// Set window position.


Scrolling Sub-Window Content

If a sub-window has a fixed or percentual size and its content becomes too big to fit in the content area, a scroll bar will appear for the particular direction. On the other hand, if the sub-window has undefined size in the direction, it will fit the size of the content and never get a scroll bar. Scroll bars in sub-windows are handled with regular HTML features, namely overflow: auto property in CSS.

As Window extends Panel, windows are also Scrollable. Note that the interface defines programmatic scrolling, not scrolling by the user. Please see "Panel".

Modal Sub-Windows

A modal window is a sub-window that prevents interaction with the other UI. Dialog windows, as illustrated in Modal Sub-Window, are typical cases of modal windows. The advantage of modal windows is limiting the scope of user interaction to a sub-task, so changes in application state are more limited. The disadvantage of modal windows is that they can restrict workflow too much.

You can make a sub-window modal with setModal(true).

subwindow modal
Modal Sub-Window

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

Security Warning

Modality of child windows is purely a client-side feature and can be circumvented with client-side attack code. You should not trust in the modality of child windows in security-critical situations such as login windows.