How to use UserStoppedTypingBehavior from ControlTemplate?

In my .NET MAUI app, I have created a custom search control and ControlTemplate for it. When I'm running the app and perform search the SearchCommand is not getting fired.

If I add the Entry control directly to TestPage and add behavior then its working.

<Entry Grid.Row="0"
       HorizontalOptions="FillAndExpand"
       Placeholder="type here...">
        <Entry.Behaviors>
            <toolkit:UserStoppedTypingBehavior
                Command="{Binding Path=SearchCommand}"
                StoppedTypingTimeThreshold="1000"
                MinimumLengthThreshold="3"
                ShouldDismissKeyboardAutomatically="True" />
        </Entry.Behaviors>
</Entry>

Custom control

/// <summary>
/// Represents an Entry control styled to contain a search icon
/// and trigger a new search command when the entry text changes.
/// </summary>
public class SearchField : MobileContentViewBase
{
    //Logic of custom control 

    private Entry _searchFieldEntry;
    private const string SearchFieldEntryName = nameof(_searchFieldEntry);

    protected override void AddCustomHandlers()
    {
        if (_searchFieldEntry == null)
        {
            _searchFieldEntry = this.FindChildByClassId<Entry>(SearchFieldEntryName);
        }
    }
}

App.xaml

<ControlTemplate x:Key="SearchFieldTemplate">
    <StackLayout>
        <ctrls:IconButton
            ImageSource="Search"
            BackgroundColor="Transparent" />

        <Entry
            ClassId="_searchFieldEntry"
            HorizontalOptions="FillAndExpand"
            VerticalOptions="FillAndExpand">
            <Entry.Behaviors>
                <toolkit:UserStoppedTypingBehavior
                    Command="{Binding Path=BindingContext.SearchCommand}"
                    StoppedTypingTimeThreshold="1000"
                    MinimumLengthThreshold="3"
                    ShouldDismissKeyboardAutomatically="True" />
            </Entry.Behaviors>
        </Entry>
    </StackLayout>
</ControlTemplate>
<Style TargetType="ctrls:SearchField">
    <Setter Property="ControlTemplate" Value="{StaticResource Key=SearchFieldTemplate}" />
</Style>

TestPage.xaml

<myCtrl:SearchField
    x:Name="searchField"
    Grid.Row="0"
    HorizontalOptions="FillAndExpand"
    Placeholder="Search here..." />

TestPageViewModel.cs

public ICommand SearchCommand { get; set; }

public TestPageViewModel()
{
    SearchCommand = new Command<string>(PerformSearch);
}

private void PerformSearch(string searchTerms)
{
    PerformedSearches += $"Performed search for '{searchTerms}'{Environment.NewLine}";
}

Instead of simple Binding I have tried TemplateBinding as well with Entry control which is in SearchFieldTemplate but it throws an InvalidOperationException.

Does anyone know how to make it work? Any help will be highly appreciated.

Behaviours don't have unique visual tree parents so we cannot use RelativeSource binding on it. You could also refer to this issue: Relativesource bindings and behaviors.

Workaround:
Although we cannot use RelativeSource binding for behavior, we could use TemplateBinding for Entry or StackLayout, then refer to it. Consider the code below:

In App.xaml:

<Entry x:Name="myentry" BindingContext="{Binding BindingContext, Source={RelativeSource TemplatedParent}}"
    ClassId="_searchFieldEntry"
    HorizontalOptions="FillAndExpand"
    VerticalOptions="FillAndExpand">
    <Entry.Behaviors>
        <toolkit:UserStoppedTypingBehavior
            Command="{Binding Path=BindingContext.SearchCommand,Source={x:Reference myentry}}"
            StoppedTypingTimeThreshold="1000"
            MinimumLengthThreshold="3"
            ShouldDismissKeyboardAutomatically="True" />
    </Entry.Behaviors>
</Entry>

In the above code, we first use TemplateBinding to set the BindingContext for Entry (x:Name="myentry"). Then for Behavior set the Binding Source to the Entry.

Hope it works.