c# - Blazor MatAutocompletelist throwing System.ArgumentNullException

Question

I'm building hotel service web application and I'm want to use MatBlazor component called MatAutocompleteList for choosing clients for reservations I've encountered an issue when Client is selected like on the screen

And I remove this value leaving it blank and press enter application throws an exception:

System.ArgumentNullException: Value cannot be null. (Parameter 'model')
   at Microsoft.AspNetCore.Components.Forms.FieldIdentifier..ctor(Object model, String fieldName)
   at Microsoft.AspNetCore.Components.Forms.FieldIdentifier.Create[TField](Expression`1 accessor)
   at Microsoft.AspNetCore.Components.Forms.ValidationMessage`1.OnParametersSet()
   at Microsoft.AspNetCore.Components.ComponentBase.CallOnParametersSetAsync()
   at Microsoft.AspNetCore.Components.ComponentBase.SetParametersAsync(ParameterView parameters)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.SetDirectParameters(ParameterView parameters)

Heres the usage of a component:

@using HotelServiceSystem.Entities
@using HotelServiceSystem.Features
@using HotelServiceSystem.Interfaces.Services
@using HotelServiceSystem.Core
@inject IHotelReservationService hotelReservationService
@inject IClientService clientService
@inject IRoomService roomService

<EditForm Model="@ReservationModel" OnValidSubmit="@SaveReservation">
    <FluentValidationValidator/>
    @if (ClientList != null && ClientList.Any())
    {
            <MatAutocompleteList Items="@ClientList.ToArray()" TItem="Client" CustomStringSelector="@(i => i.FirstName + " " + i.LastName)" Label="Choose client" @bind-Value="@ReservationModel.Client" FullWidth="@true" ShowClearButton="@true">
                <ItemTemplate Context="template">
                    <div style="display: flex; flex-direction: row; width: 100%;">
                        <div>@template.FirstName @template.LastName @template.PhoneNumber</div>
                    </div>
                </ItemTemplate>
            </MatAutocompleteList>
    }
    else
    {
        <p>First u need to add clients</p>
    }
    <ValidationMessage For="@(()=> ReservationModel.Client.Id)"></ValidationMessage>
    <HssInputCustom Caption="Number of guests" @bind-Value="ReservationModel.NumberOfGuests"/>
    <div class="col-12 row">
        <label class="col-2">Date From</label>
        <MatDatePicker class="form-control col-3" @bind-Value="ReservationModel.DateFrom"/>
    </div>
    <div class="col-12 row">
        <label class="col-2">Date to</label>
        <MatDatePicker class="form-control col-3" @bind-Value="ReservationModel.DateTo"/>
        <ValidationMessage For="@(() => ReservationModel.DateTo)"></ValidationMessage>
    </div>
    <div class="form-group">
        <HSSMultiSelector Selected="@_selected" NotSelected="@_notSelected"/>
    </div>
    <HssInputCustom Caption="Price" @bind-Value="ReservationModel.Price"/>
    <HssInputCustom Caption="Discount" @bind-Value="ReservationModel.Discount"/>
    <div class="col-12 row">
        <span class="col-2"></span>
        <input type="submit" class="form-control col-1 btn btn-primary" value="Submit"/>
    </div>
</EditForm>

@code {
    private HotelReservation ReservationModel { get; set; }
    private readonly List<MultiSelector> _selected = new List<MultiSelector>();
    private List<MultiSelector> _notSelected = new List<MultiSelector>();
    private List<Room> _selectedRooms = new List<Room>();
    private List<Room> RoomList { get; set; }
    private List<Client> ClientList { get; set; }
    private List<string> ClientIdList { get; set; }

    [Parameter]
    public EventCallback<HotelReservation> OnReservationAdd { get; set; }

    protected override async Task OnInitializedAsync()
    {
        RoomList = roomService.GetAllRoomsAsync();
        ClientList = clientService.GetAllClients();
        ReservationModel = new HotelReservation {Client = new Client()};
        _notSelected = RoomList.Select(x => new MultiSelector(x.Id.ToString(), $"Room Number : {x.RoomIdentifier}")).ToList();
        await base.OnInitializedAsync();
    }
    

    private async Task SaveReservation()
    {
        _selectedRooms = RoomList.Where(x => _selected.Any(y => y.Key == x.Id.ToString())).ToList();

        _selectedRooms.ForEach( x=> ReservationModel.RoomReservations.Add(new RoomReservation
        {
            Reservation = ReservationModel,
            Room = x
        }));

        await hotelReservationService.AddHotelReservationAsync(ReservationModel);
        await OnReservationAdd.InvokeAsync(ReservationModel);
        ReservationModel = new HotelReservation() {Client = new Client()};
    }
}

Also my model to which I'm binding value is created properly.

 private Client _selectedClient = new Client();

I've no clue how I can prevent user from doing that, or if I can somehow catch this exception. Maybe someone had a similar issue. Much appriciate help!

Answer 1

我确实设法以简单的方式解决了这个问题。我为我的模型客户端对象创建了属性，并在这个属性中创建了一个空检查

private Client _selectedClient
{
    get
    {
        if (ReservationModel.Client == null)
        {
            return new Client()
            {
                CompanyName = "",
                Email = "",
                FirstName = "",
                LastName = "",
                PhoneNumber = "",
                Id = 0
            };
        }

        return ReservationModel.Client;

    }
    set => ReservationModel.Client = value;
}

现在在代码中调用属性来为我的模型设置和获取值。