MetroTabControl looks like a styled TabControl and adds three things: a close button per tab, a say in whether tab contents survive a switch, and a margin for the strip.

<mah:MetroTabControl>
    <mah:MetroTabItem Header="General" CloseButtonEnabled="True">
        <TextBlock Margin="10" Text="First page" />
    </mah:MetroTabItem>
    <mah:MetroTabItem Header="Display" CloseButtonEnabled="True">
        <TextBlock Margin="10" Text="Second page" />
    </mah:MetroTabItem>
</mah:MetroTabControl>

Its style is based on MahApps.Styles.TabControl, so everything on the TabControl styles page applies: the placement triggers, the underline through TabControlHelper, the large header font. On develop it has the two WinUI looks as well, under MahApps.Styles.MetroTabControl.WinUI and MahApps.Styles.MetroTabControl.WinUI.SelectorBar, each keeping the template this control brings.

Bind ItemsSource and you do not have to make the items yourself — GetContainerForItemOverride hands back a MetroTabItem, not a plain TabItem, so the close button is available either way.

Keeping the visual tree

This is the property worth knowing about, and it works by swapping the template outright:

<mah:MetroTabControl KeepVisualTreeInMemoryWhenChangingTabs="True" />

Closing tabs

A tab goes only when everyone who was asked agrees. Once a close button is clicked:

1. the item's own CloseTabCommand, if it has one, is asked whether it can run. A No keeps the tab and ends it there; a Yes runs the command. See MetroTabItem.
2. the closing event is raised, and any handler can say no.
3. the control's CloseTabCommand, if it has one, is asked and run. The removal is then whoever handles it to do.
4. with no command on the control, the item is taken out: of Items when there is no ItemsSource, of the bound collection otherwise, matching either the container or its DataContext.

Saying no

private void OnTabItemClosing(object sender, BaseMetroTabControl.TabItemClosingEventArgs e)
{
    if (e.ClosingTabItem.Header.ToString() == "Home")
    {
        e.Cancel = true;
    }
}

<mah:MetroTabControl TabItemClosing="OnTabItemClosing" />

TabItemClosingEventArgs derives from CancelEventArgs, so e.Cancel = true keeps the tab where it is. Every handler is given args of its own and the first one to cancel is the last one asked.

Taking your time over the answer

A handler that has to ask somebody before it answers asks for a deferral first. The closing waits for it, so the answer can arrive after a dialog, a save or a call over the wire, and the handler can be async.

private async void OnTabItemClosing(object sender, BaseMetroTabControl.TabItemClosingEventArgs e)
{
    using var deferral = e.GetDeferral();

    var answer = await this.ShowMessageAsync("Close this tab?",
                                             "What is in it has not been saved.",
                                             MessageDialogStyle.AffirmativeAndNegative);

    e.Cancel = answer != MessageDialogResult.Affirmative;
}

GetDeferral hands back a TabItemClosingDeferral, and the closing goes on once it is completed. A using declaration completes it when the handler returns, which is what the example relies on; Complete() does it by hand, and saying it twice does nothing.

Nothing changes for a handler that does not ask for one. With no deferral taken the whole thing stays synchronous, exactly as it was.

The command on the control

<mah:MetroTabControl CloseTabCommand="{Binding CloseDocumentCommand}" />

The parameter is the item's CloseTabCommandParameter if it has one, otherwise the MetroTabItem itself.

TabStripMargin

Room around the tabs without moving the content — useful when the strip shares a row with something of your own, such as a "new tab" button.

The animated siblings

Two more controls share the same base, BaseMetroTabControl, and therefore the same closing behaviour, TabStripMargin and item type:

They are separate controls, not styles. The equivalents for a plain TabControl are MahApps.Styles.TabControl.Animated and MahApps.Styles.TabControl.AnimatedSingleRow — see TabControl.

Neither of those two exposes KeepVisualTreeInMemoryWhenChangingTabs; it is declared on MetroTabControl itself.