MahApps.Metro - MetroTabControl

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.

A MetroTabControl with close buttons

<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.

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

Property	Type	Default
`KeepVisualTreeInMemoryWhenChangingTabs`	`bool`	`False`	keep every tab's content alive instead of rebuilding it

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

	template	what the content is
`False`	`MahApps.Templates.MetroTabControl.DoNotKeepVisualTreeInMemory`	a `ContentPresenter` bound to `SelectedContent`, as WPF does it — the old page is discarded on every switch
`True`	`MahApps.Templates.MetroTabControl.KeepVisualTreeInMemory`	a `PART_ItemsHolder` that the `TabControlEx` base fills with one container per tab and shows or hides

<mah:MetroTabControl KeepVisualTreeInMemoryWhenChangingTabs="True" />

Turn it on when rebuilding a page is expensive or throws away state — a half-filled form, a scroll position, a loaded document, a WebView. Leave it off when the tabs are many or heavy, because every one of them then stays realised for the lifetime of the control.

MetroTabControl derives from TabControlEx (ControlzEx), which is where the holder mechanism comes from. Note that it is the template that decides: a template of your own without PART_ItemsHolder will not keep anything, whatever the property says.

Closing tabs

CloseTabCommand on the control replaces the whole removal:

Property	Type
`CloseTabCommand`	`ICommand`	run instead of removing the tab

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

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

When this command is set, the control does not remove the tab and does not raise TabItemClosingEvent — it runs the command and stops. Removing the item is then yours to do.

With no command set, the control raises a cancellable event instead:

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

<mah:MetroTabControl TabItemClosingEvent="OnTabItemClosing" />

TabItemClosingEventArgs derives from CancelEventArgs, so e.Cancel = true keeps the tab. Left alone, the control removes the item — from Items when there is no ItemsSource, and from the bound collection otherwise, matching either the container or its DataContext.

The whole order, once a close button is clicked:

the item's own CloseTabCommand, if set, runs — see MetroTabItem;
the control's CloseTabCommand, if set, runs and nothing further happens;
otherwise TabItemClosingEvent is raised, and unless it is cancelled the item is removed.

TabStripMargin

Property	Type	Default
`TabStripMargin`	`Thickness`	`0`	margin around the header strip

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:

Control
`MetroAnimatedTabControl`	fades the page in when the tab changes
`MetroAnimatedSingleRowTabControl`	the same, with a strip that scrolls rather than wraps

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.