practice/practiceApplicaiton/ReportPage.xaml.cs

namespace practiceApplicaiton;

public partial class ReportPage : ContentPage
{
    public ReportPage()
    {
        InitializeComponent();
        DateFrom.Date = DateTime.Today.AddMonths(-1);
        DateTo.Date   = DateTime.Today;
    }

    private async void OnGenerateClicked(object sender, EventArgs e)
    {
        if (DateTo.Date < DateFrom.Date)
        {
            await DisplayAlert("Ошибка", "Дата «По» не может быть раньше «С»", "OK");
            return;
        }

        try
        {
            var data = await Repository.GetBookingReportAsync((DateTime)DateFrom.Date, (DateTime)DateTo.Date);
            ReportList.ItemsSource = data;

            var total = data.Sum(b => b.TotalCost);
            TotalLabel.Text = $"{total:N0} ₽";
        }
        catch (Exception ex)
        {
            await DisplayAlert("Ошибка", ex.Message, "OK");
        }
    }
}