[DefaultValue(null)]
[Parameter]
public EventCallback<int> ActiveTabIndexChanged { get; set; }

<DxRibbon ActiveTabIndexChanged="OnActiveTabIndexChanged">
    <DxRibbonTab Text="Home">
        <DxRibbonGroup Text="File">
            <DxRibbonItem Text="New" IconCssClass="dx-icon-file" />
            <DxRibbonItem Text="Save" IconCssClass="dx-icon-save" />
        </DxRibbonGroup>
        <DxRibbonGroup Text="Clipboard">
            <DxRibbonItem Text="Cut" IconCssClass="dx-icon-cut" />
            <DxRibbonItem Text="Copy" IconCssClass="dx-icon-copy" />
            <DxRibbonItem Text="Paste" IconCssClass="dx-icon-paste" />
        </DxRibbonGroup>
    </DxRibbonTab>
    <DxRibbonTab Text="Format">
        <DxRibbonGroup Text="Align">
            <DxRibbonItem Text="Left" IconCssClass="dx-icon-alignleft" />
            <DxRibbonItem Text="Center" IconCssClass="dx-icon-aligncenter" />
            <DxRibbonItem Text="Right" IconCssClass="dx-icon-alignright" />
        </DxRibbonGroup>
    </DxRibbonTab>
</DxRibbon>

<p>You selected tab #@ActiveTabIndex.</p>

@code {
    int ActiveTabIndex=1;

    void OnActiveTabIndexChanged(int index)
    {
        ActiveTabIndex = index+1;
    }
}