AspNetCore 2.1 BackgroundService\IHostedService 中的 FileSystemWatcher答案

【问题标题】：FileSystemWatcher in an AspNetCore 2.1 BackgroundService\IHostedServiceAspNetCore 2.1 BackgroundService\IHostedService 中的 FileSystemWatcher
【发布时间】：2018-12-05 17:06:27
【问题描述】：

我正在尝试在 AspNet Core 2.1 应用程序中使用 BackgroundService 的实现。我在ExecuteAsync 中创建了一个 FileSystemWatcher 并链接了关联的事件，但是，fsw 事件要么永远不会被触发（无法访问？已经被处理？），要么是我做错了异步或范围搞砸了。我似乎无法弄清楚。以下是相关代码。

public class FSWImpl : BackgroundService
{
    private readonly IHostingEnvironment _env;
    private readonly ILogger<LiftAndShift> _logger;
    private FileSystemWatcher _fsw;

    public LiftAndShift(IHostingEnvironment env, ILogger<FSWImpl> logger)
    {
        _env = env;
        _logger = logger;
    }

    protected override Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("Creating new FSW");
        var path = Path.Combine(_env.ContentRootPath, "WebData");
        _fsw = new FileSystemWatcher(path,"*.json");
        _fsw.Created += _fsw_Created;
        _fsw.Changed += _fsw_Changed;
        _fsw.Renamed += _fsw_Renamed;
        _fsw.Error += _fsw_Error;
        return Task.CompletedTask;
    }

    private void _fsw_Error(object sender, ErrorEventArgs e) => _logger.LogInformation("File error");
    private void _fsw_Renamed(object sender, RenamedEventArgs e) => _logger.LogInformation("File Renamed");
    private void _fsw_Changed(object sender, FileSystemEventArgs e) => _logger.LogInformation("File changed");
    private void _fsw_Created(object sender, FileSystemEventArgs e) => _logger.LogInformation("File created");
}

我在启动时将此服务注册为services.AddHostedService<FSWImpl>();

【问题讨论】：

这行得通吗？ services.AddHostedService();将其添加为瞬态，这会在 ExecuteAsync 返回后不久破坏 FSWImpl 和 FileSystemWatcher 对象。因此，该文件将不再被观看。

标签： asp.net-core filesystemwatcher asp.net-core-2.1

【解决方案1】：

要启用FileSystemWatcher，您需要将EnableRaisingEvents 设置为True。

演示代码：

        protected override Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("Creating new FSW");
        var path = Path.Combine(_env.ContentRootPath, "WebData");
        _fsw = new FileSystemWatcher(path, "*.json");
        _fsw.Created += _fsw_Created;
        _fsw.Changed += _fsw_Changed;
        _fsw.Renamed += _fsw_Renamed;
        _fsw.Error += _fsw_Error;
        _fsw.EnableRaisingEvents = true;
        return Task.CompletedTask;
    }

FileSystemWatcher.cs

    //
    // Summary:
    //     Gets or sets a value indicating whether the component is enabled.
    //
    // Returns:
    //     true if the component is enabled; otherwise, false. The default is false. If
    //     you are using the component on a designer in Visual Studio 2005, the default
    //     is true.
    //
    // Exceptions:
    //   T:System.ObjectDisposedException:
    //     The System.IO.FileSystemWatcher object has been disposed.
    //
    //   T:System.PlatformNotSupportedException:
    //     The current operating system is not Microsoft Windows NT or later.
    //
    //   T:System.IO.FileNotFoundException:
    //     The directory specified in System.IO.FileSystemWatcher.Path could not be found.
    //
    //   T:System.ArgumentException:
    //     System.IO.FileSystemWatcher.Path has not been set or is invalid.
    public bool EnableRaisingEvents { get; set; }

【讨论】：