从任意线程调用 StateHasChanged() 是否安全？

Question

从任意线程调用 StateHasChanged() 安全吗？

让我给你一些背景信息。想象一个服务器端 Blazor/Razor 组件应用程序，您有：

从任意线程引发 BreakingNews 事件的单例服务 NewsProvider。
一个组件 News.cshtml 获取服务注入并订阅 BreakingNews 事件。引发事件时，组件更新模型并调用 StateHashChanged()

NewsProvider.cs

using System;
using System.Threading;

namespace BlazorServer.App
{
    public class BreakingNewsEventArgs: EventArgs
    {
        public readonly string News;

        public BreakingNewsEventArgs(string news)
        {
            this.News = news;
        }
    }

    public interface INewsProvider
    {
        event EventHandler<BreakingNewsEventArgs> BreakingNews;
    }

    public class NewsProvider : INewsProvider, IDisposable
    {

        private int n = 0;

        public event EventHandler<BreakingNewsEventArgs> BreakingNews;
        private Timer timer;

        public NewsProvider()
        {
            timer = new Timer(BroadCastBreakingNews, null, 10, 2000);

        }

        void BroadCastBreakingNews(object state)
        {
            BreakingNews?.Invoke(this, new BreakingNewsEventArgs("Noticia " + ++n));
        }

        public void Dispose()
        {
            timer.Dispose();
        }
    }
}

News.cshtml

@page "/news"
@inject INewsProvider NewsProvider
@implements IDisposable

<h1>News</h1>

@foreach (var n in this.news)
{
    <p>@n</p>
}


@functions {
    EventHandler<BreakingNewsEventArgs> breakingNewsEventHandler;

    List<string> news = new List<string>();

    protected override void OnInit()
    {
        base.OnInit();
        breakingNewsEventHandler = new EventHandler<BreakingNewsEventArgs>(OnBreakingNews);
        this.NewsProvider.BreakingNews += breakingNewsEventHandler;
    }

    void OnBreakingNews(object sender, BreakingNewsEventArgs e)
    {
        this.news.Add(e.News);
        StateHasChanged();
    }

    public void Dispose()
    {
        this.NewsProvider.BreakingNews -= breakingNewsEventHandler;
    }
}

Startup.cs

using Microsoft.AspNetCore.Blazor.Builder;
using Microsoft.Extensions.DependencyInjection;
using BlazorServer.App.Services;

namespace BlazorServer.App
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            // Since Blazor is running on the server, we can use an application service
            // to read the forecast data.
            services.AddSingleton<WeatherForecastService>();
            services.AddSingleton<INewsProvider, NewsProvider>();
        }

        public void Configure(IBlazorApplicationBuilder app)
        {
            app.AddComponent<App>("app");
        }
    }
}

它显然有效，但我不知道 StateHasChanged() 是否线程安全。如果不是，我怎样才能安全地调用 StateHashChanged()？。有没有类似于Control.BeginInvoke的东西？我应该使用 SyncrhonizationContext.Post 吗？

Answer 1

不，从任意线程调用 StateHasChanged() 是不安全的。

调用 StateHasChanged() 的正确方法是使用 InvokeAsync()

void OnBreakingNews(object sender, BreakingNewsEventArgs e)
{
    InvokeAsync(() => {
        news.Add(e.News);
        StateHasChanged();
    });
}

从任意线程调用 StateHasChanged() 是否安全？

Is it safe to call StateHasChanged() from an arbitrary thread?

c#

blazor

blazor-server-side

NewsProvider.cs

News.cshtml

Startup.cs