23

StateHasChanged()从任意线程调用是否安全？

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

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

新闻提供者.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();
        }
    }
}

新闻.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;
    }
}

启动.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，但我不知道是否StateHasChanged()是线程安全的。如果不是，我怎么能StateHashChanged()安全地打电话？有没有类似的东西Control.BeginInvoke？我应该使用SyncrhonizationContext.Post吗？

4

1 回答 1

39

不，从任意线程调用StateHasChanged()是不安全的。

正确的调用方式StateHasChanged()是使用InvokeAsync()

void OnBreakingNews(object sender, BreakingNewsEventArgs e)
{
    InvokeAsync(() => {
        news.Add(e.News);
        StateHasChanged();
    });
}
于 2019-02-04T17:05:30.620 回答