I'm testing blazor server (.net 6.05) on one of our projects and I have a following code:

@page "/"
@using Microsoft.EntityFrameworkCore

@using Microsoft.JSInterop
@inject IDbContextFactory<MyDbContext> DbContextFactory;


@code {
    [Inject]
    private IHttpContextAccessor HttpContextAccessor { get; set; } = default!;

    MyDbContextContext { get; set; }
    public Dish? RandomDish { get; set; }
    public Region? Region { get; set; }


    async Task getRandomDish()
    {
        var dish = await Context.Dishes.OrderBy(m => Guid.NewGuid()).FirstOrDefaultAsync();
        RandomDish = dish;
    }

    async Task SaveDishName()
    {
        await Context.SaveChangesAsync();
    }

    protected override async Task OnInitializedAsync()
    {

        var a = HttpContextAccessor.HttpContext.User.Identity;
        Context = await DbContextFactory.CreateDbContextAsync();
        Region = await Context.Regions.SingleOrDefaultAsync(m => m.Name == "Italy");
        await getRandomDish();

    }
     protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (!firstRender) return;

    }
}

<PageTitle>Index</PageTitle>

@if (RandomDish != null)
{
    <h1>@RandomDish?.Name</h1>
    <h2>@RandomDish?.DishId</h2>
    <p>@Region?.Borders?.AsText()</p>
}<-- it errors here
<button @onclick="@(async () => await getRandomDish())">GET NEW DISH</button>

<div>
    Change dish name
    <input @bind="RandomDish.Name" />
    <button @onclick="@(async () => await SaveDishName())">Save</button>
</div>

When I run the code, it throws following exception

System.NullReferenceException: 'Object reference not set to an instance of an object.'

****.Cms.Web.Pages.Index.RandomDish.get returned null.

I also tried "is not null" and referenceEquals(RandomDish, null), but always the same issue.

How am I supposed to do a null check, if getters will throw nulls :/

Issue disappears if I initialize dish with line under, but that's not a solution to a problem I guess.

public Dish? RandomDish { get; set; } = new Dish();

CodePudding user response：

You cannot have a null in @bind.

<input @bind="RandomDish.Name" />

Surround the Save block with @if (RandomDish != null) or something similar.

CodePudding user response：

Are you sure your expressions in the markup are being interpreted rightly? Try @(RandomDish?.Name) and @(RandomDish?.DishId) just to be sure. I suspect that @RandomDish?.Name might be interpreted as @RandomDish then a literal "?.Name".