TabSheet - CUBA Platform. Developer’s Manual

4.5.2.2.11. TabSheet

TabSheet container is a tabbed panel. The panel shows content of one tab at a time.

XML-name of the component: tabSheet.

An example description of a tabbed panel in a screen XML-descriptor:

<tabSheet>
    <tab id="mainTab" caption="Tab1" margin="true" spacing="true">
        <dateField datasource="orderDs" property="date" caption="Date"/>
        <lookupField datasource="orderDs" property="customer" optionsDatasource="customersDs" caption="Customer"/>
    </tab>
    <tab id="additionalTab" caption="Tab2" margin="true" spacing="true">
        <textField datasource="orderDs" property="amount" caption="Amount"/>
    </tab>
</tabSheet>

The tabSheet component should contain nested tab elements describing tabs. Each tab is a container with a vertical components layout similar to vbox.

tab element attributes:

id – tab identifier. Please note that tabs are not components and their IDs are used only within a TabSheet in order to work with tabs from the controller.
caption – tab caption.

closable - defines whether the x button for closing the tab is displayed. Default value is false.
icon - defines icon location in theme catalog. Applicable only for the Web Client. Detailed information on recommended icon placement is available in Themes.

lazy – sets lazy loading for tab content.

Lazy tabs do not load their content when the screen is opened, which reduces the number of components in memory. Components within a tab are loaded only when a user selects the tab. Additionally, if a lazy-tab includes visual components linked to a data source containing a JPQL query, this query is not executed as well. As a result, screen opens faster, and data is loaded only when the user requests it by selecting this tab.

Please note that the components located on a lazy tab do not exist when the screen is opened. Therefore they cannot be injected into a controller and cannot be obtained by invoking getComponent() in the controller’s init() method. The lazy tab components can be accessed only after the user opens the tab. This moment may be intercepted using TabSheet.SelectedTabChangeListener, for example:
```
@Inject
private TabSheet tabsheet;

private boolean detailsInitialized, historyInitialized;

@Override
public void init(Map<String, Object> params) {
    tabsheet.addSelectedTabChangeListener(event -> {
        if ("detailsTab".equals(event.getSelectedTab().getName())) {
            initDetails();
        } else if ("historyTab".equals(event.getSelectedTab().getName())) {
            initHistory();
        }
    });
}

private void initDetails(){
    if (detailsInitialized) {
        return;
    }
    // use getComponentNN("comp_id") here to get tab's components
    detailsInitialized=true;
}

private void initHistory(){
    if (historyInitialized) {
        return;
    }
    // use getComponentNN("comp_id") here to get tab's components
    historyInitialized = true;
}
```
By default, tabs are not lazy, which means that all their content is loaded when a screen is opened.

detachable – when it is true, a tab can be detached to a separate window in a screen desktop implementation. It enables, for example, different parts of the application UI to be located on different monitors. A detachable tab has a special button in its header:

TabSheet styles

In Web Client with a Halo-based theme, you can set predefined styles to the TabSheet container using the stylename attribute either in the XML descriptor or in the screen controller:

<tabSheet stylename="framed">
    <tab id="mainTab" caption="Framed tab"/>
</tabSheet>

When setting a style programmatically, select one of the HaloTheme class constants with the TABSHEET_ prefix:

tabSheet.setStyleName(HaloTheme.TABSHEET_COMPACT_TABBAR);

centered-tabs - centers the tabs inside the tab bar. Works best if all the tabs fit completely in the tab bar (i.e. no tab bar scrolling).

compact-tabbar - reduces the whitespace around the tabs in the tab bar.

equal-width-tabs - gives equal amount of space to all tabs in the tab bar (i.e. expand ratio == 1 for all tabs). The tab captions will be truncated if they do not fit into the tab. Tab scrolling will be disabled when this style is applied (all tabs will be visible at the same time).

framed - adds a border around the whole component as well as around individual tabs in the tab bar.

icons-on-top - displays tab icons on top of the tab captions (by default the icons are place on the left side of the caption).

only-selected-closeable - only the selected tab has the close button visible. Does not prevent closing the tab programmatically, it only hides the button from the end user.

padded-tabbar - adds a small amount of padding around the tabs in the tab bar, so that they don’t touch the outer edges of the component.

Attributes of tabSheet: height - id - stylename - tabIndex - visible - width
Attributes of tab: caption - closable - detachable - enable - expand - margin - icon - id - lazy - spacing - stylename - visible
Predefined styles of tabSheet: centered-tabs - compact-tabbar - equal-width-tabs - framed - framed - only-selected-closeable - padded-tabbar
Listeners of tabSheet: SelectedTabChangeListener