GridEvents OnActionBegin definition causes no edit dialog

//Grid definition contains:
<GridEvents OnActionBegin="OnActionBegin" TValue="MyClass"></GridEvents>
<EjsDataManager AdaptorInstance="@typeof(MyCustomAdaptor)"
                Adaptor="Adaptors.CustomAdaptor">
</EjsDataManager>
<GridEditSettings AllowAdding="true"
                  AllowDeleting="true"
                  AllowEditing="true"
                  Mode="@EditMode.Dialog">
    <Template>
        @{
            var myObj = (context as MyClass);
            <MyEditor MyFiled="@myObj" MyDialogMessageProvider="@_myDialogMessageProvider"/>
        }
    </Template>
</GridEditSettings>

//code of OnActionBegin:
public void OnActionBegin(ActionEventArgs<MyClass> args)
{
    if (args.Action == "add")
    {
        //args.Data validations here
        {
            //prevent close dialog and show message code here
            args.Cancel = true;
        }
    }
}