Blazor MatAutocompletelist抛出System.ArgumentNullException [英] Blazor MatAutocompletelist throwing System.ArgumentNullException

问题描述

我正在构建酒店服务Web应用程序，并且我想使用名为MatAutocompleteList的MatBlazor组件来选择要预订的客户端，当在屏幕上选择客户端"时遇到了问题

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

我删除了该值并将其留为空白，然后按Enter应用程序将引发异常:

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)

在这里使用组件:

@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()};
    }
}

也正确创建了我要绑定值的模型.

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

 private Client _selectedClient = new Client();

我不知道如何阻止用户这样做，或者是否可以以某种方式捕获此异常.也许有人遇到过类似的问题.很有帮助！

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!

推荐答案

我确实设法以简单的方式解决了此问题.我已经为模型客户端对象创建了属性，并且在此属性中，我创建了一个空检查

I did manage to resolve this issue in simple way. I've created property for my model client object and in this propery I've created a null check

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;
}

现在在代码中我调用属性来设置和获取模型的值.

and now in code im calling property to set and get value for my model.

这篇关于Blazor MatAutocompletelist抛出System.ArgumentNullException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！