Question

tl; dr

#!/usr/bin/perl

use 5.010;
use strict; 
use warnings;


my ($inputfilename, $outtextfilename, $outbinfilename) = @ARGV;
open(my $in, '<:encoding(UTF-8)', $inputfilename)
  or die "Could not open file '$inputfilename' $!";

open my $outtext, '>', $outtextfilename or die;

my $outbin;
open $outbin, '>', $outbinfilename or die;
binmode $outbin;


while (my $aline = <$in>) {
  chomp $aline;
  if($aline =~ /\<\/FileSystem\>/) {   # a match indicates the end of the text portion - the rest is binary
    print $outtext "$aline\n";  # last line of the text portion
    print  "$aline\n";  # last line of the text portion
    close ($outtext); 

    binmode $in;  # change input file to binary? 
    # what do I do here to copy all remaining bytes in file as binary to $outbin??
    die;
    } else {
    print $outtext  "$aline\n";   # a line of the text portion
    print "$aline\n";   # a line of the text portion
    }
}

close ($in);
close ($outbin);

在经典SignalR Chat应用的一个变体中，我监视对SQL Server表的更改，并通过SignalR实时报告它们。观看this video 10秒钟以了解主意。我的代码改编自this project。聊天部分工作正常。

对SQL Server表的更改应该由类services.AddSingleton<ISomeService, SomeService>(); // SomeService not instantiated nor initialized?监视。但是，它的构造函数永远不会被调用，因此应该在这里获取对SignalR集线器的引用。

这是我的Startup.ConfigureServices：

SqlDependencyService

这是我的SqlDependencyService类的一部分：

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<ApplicationDbContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

    services.AddSignalR();

    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

    // No instantiation ?!?
    services.AddSingleton<IDatabaseChangeNotificationService, SqlDependencyService>();

    // My lame attempt at forcing instantiation:
    SqlDependencyService sqlDS = serviceProvider.GetService<SqlDependencyService>();
    //sqlDS.Config(); // Fails, sqlDS is null.
}

这是服务的界面：

public class SqlDependencyService : IDatabaseChangeNotificationService
    {
        private readonly IConfiguration configuration;
        private readonly IHubContext<ChatHub> chatHub;

        // Never gets called!        
        public SqlDependencyService(IConfiguration configuration, IHubContext<ChatHub> chatHub)
        {
            this.configuration = configuration;
            this.chatHub = chatHub;
        }

        // Never gets called!    
        public void Config()
        {
            SubscribeToPersonTableChanges();
        }

        private void SubscribeToPersonTableChanges()
        {
            // ...
        }

        // ...
    }

如前所述，从不调用构造函数。另外，我看不到如何调用Config方法-一些ASP.NET Core约定魔术？

HomeController没有这个问题，它的构造函数被调用并传递了public interface IDatabaseChangeNotificationService { void Config(); }：

IHubContext<ChatHub>

Answer 1

仅添加服务不会导致实例化，实际上您需要将其注入到容器中以调用其构造函数。看来您希望该服务在启动时可用，所以我建议在启动时使用Configure方法：

public void Configure(IApplicationBuilder app, IDatabaseChangeNotificationService dbService)
{
    dbService.Config();

    //snip
}

services.AddSingleton，永远不会调用服务的构造函数

1 个答案: