如何在Xamarin.Forms WebView OnBackButtonPressed中检测按下back按钮时多个实例的活动窗口

public class CustomWebView : WebView
{
    public event EventHandler<EventArgs> BackButtonPressed;

    protected override bool OnBackButtonPressed()
    {
        BackButtonPressed?.Invoke(this, EventArgs.Empty);

        // 检测多个实例的活动窗口逻辑
        if (Application.Current.MainPage.Navigation.NavigationStack.Count > 1)
        {
            // 多个实例的活动窗口存在，执行返回操作
            Application.Current.MainPage.Navigation.PopAsync();
            return true;
        }
        else
        {
            // 多个实例的活动窗口不存在，执行默认返回操作
            return base.OnBackButtonPressed();
        }
    }
}