我正在我们的一个项目上测试blazor服务器(.net 6.05),我有以下代码:
@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>
当我运行代码时,它会引发以下异常
系统NullReferenceException:"对象引用未设置为
****.Cms.网状物页.指数随机培养皿.get返回null.
我还try 了"is not null"和referenceEquals(RandomDish,null),但始终是相同的问题.
如果getter将抛出null,我应该如何执行null判断:/
如果我用下面的行初始化dish,问题就会消失,但我想这并不是问题的解决方案.
public Dish? RandomDish { get; set; } = new Dish();