Overlay bottom tab bar with a custom view in Xamarin Forms

1. Create a view (Grid, Stack, Frame...) that implements SignKeys.Effects.ICustomTabView

    public partial class TabView : Grid, ICustomTabView
    {
        public event EventHandler<int> IndexChanged;
   
        public void OnTabSelected(int index)
        {
            //Highlight the selected tab
        }
        ...
    }
   

2. Set it as the tab view of a TabbedPage using TabEffect.

   XAML:

    <TabbedPage 
        ...
        xmlns:effects="clr-namespace:SignKeys.Effects;assembly=SignKeys.Effects.CustomTabView"
    >
        <effects:TabEffect.TabView>
            <local:TabView />
        </effects:TabEffect.TabView>
        ...
   

   CS:

    TabEffect.SetTabView(this, new TabView());
   

3. Set the view's height.

By default, the drawn view's height will be equal to its HeightRequest.

To make the view's height change dynamically based on the native tab bar's height (which varies from device to device and from orientation to orientation), use TabEffect.SetCustomTabHeight(...).

TabEffect.SetCustomTabHeight(this, new TabHeight(TabHeightMode.RelativeToNativeTabBar, 16));

The custom view will be always 16px higher than the native tab bar.

TabEffect.SetCustomTabHeight(this, new TabHeight(TabHeightMode.ProportionalToNativeTabBar, 1.2));

The custom view's height = the tab bar's height * 1.2