> Markdown version of [Sub-Windows](https://vaadin.com/docs/v8/framework/layout/layout-sub-window). Section index: [llms.txt](https://vaadin.com/docs/v8/framework/llms.txt)

# <a id="layout.sub-window"></a>Sub-Windows

[Demo](https://demo.vaadin.com/sampler/#ui/structure/window)

*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.

[Image: 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](#layout.sub-window.modal).

## <a id="layout.sub-window.openclose"></a>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:

```java
public static class SubWindowUI extends UI {
    @Override
    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();
        subWindow.setContent(subContent);

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

        // Center it in the browser window
        subWindow.center();

        // Open it in the UI
        addWindow(subWindow);
    }
}
```

The result was shown in [A Sub-Window](#figure.layout.sub-window.basic). 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.

### <a id="layout.sub-window.openclose.example"></a>Sub-Window Management

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

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

        // Disable the close button
        setClosable(false);

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

You could open the window as follows:

```java
// 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
    UI.getCurrent().addWindow(sub);
});
```

## <a id="layout.sub-window.position"></a>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.

```java
// Create a new sub-window
mywindow = new Window("My Dialog");

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

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

UI.getCurrent().addWindow(mywindow);
```

## <a id="layout.sub-window.scrolling"></a>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"](https://vaadin.com/docs/v8/framework/layout/layout-panel.md#layout.panel).

## <a id="layout.sub-window.modal"></a>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](#figure.layout.sub-window.modal), 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).

[Image: subwindow modal]

Modal Sub-Window

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

> **Warning: 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.