OrderEditForm.xaml

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:dx="http://schemas.devexpress.com/maui"
             x:Class="ValidateFormEvent.OrderEditForm"
             Title="Edit order">
    <ContentPage.ToolbarItems>
        <ToolbarItem Text="Save" Clicked="ToolbarItem_Clicked" />
    </ContentPage.ToolbarItems>
    <dx:DataFormView DataObject="{Binding Item}" x:Name="dataFormView" 
                       ValidateForm="dataFormView_ValidateForm" ValidationMode="LostFocus">
        <dx:DataFormTextItem FieldName="Product.Name" LabelText="Product"/>
        <dx:DataFormNumericItem FieldName="Product.UnitPrice" LabelText="Price"/>
        <dx:DataFormNumericItem FieldName="Quantity"/>
        <dx:DataFormDateItem FieldName="Date"/>
        <dx:DataFormCheckBoxItem FieldName="Shipped"/>
    </dx:DataFormView>
</ContentPage>