如何访问asp netcore选项，然后才能对其进行访问

Question

我有这样的选择：

public class ApplicationSettings
{
    public string Title { get; set; }

    public string PluginFolders { get; set; }
}

以及类似的服务：

public interface IWildcardResolver
{
    string Resolve(string value);
}


public class WildcardResolver : IWildcardResolver
{
    private readonly IHostingEnvironment _hostingEnvironment;

    public WildcardResolver(IHostingEnvironment hostingEnvironment)
    {
        _hostingEnvironment = hostingEnvironment;
        AddWildcard("%contentRootPath%", _hostingEnvironment.ContentRootPath);
        AddWildcard("%webRootPath%", _hostingEnvironment.WebRootPath);
        AddWildcard("%environment%", _hostingEnvironment.EnvironmentName);
    }

    private readonly Dictionary<string, string> _hardWiredValues = new Dictionary<string, string>();

    /// <inheritdoc />
    public string Resolve(string value)
    {
        var sb = new StringBuilder(value);
        foreach (var pair in _hardWiredValues)
        {
            sb.Replace(pair.Key, pair.Value);
        }

        return sb.ToString();
    }

    public void AddWildcard(string name, string value)
    {
        if (_hardWiredValues.ContainsKey(name))
            throw new Exception($"A value for the wildcard {name} already exists.");

        _hardWiredValues.Add(name, value);
    }
}

[如何确定在使用IOptions<AppSettings>通过PluginFolders通过DI访问那些设置之前（因为它包含通配符）？我已经尝试过IConfigureOptions<AppSettings>和IPostConfigureOptions<AppSettings>，但是它们似乎都发生在一个阶段太晚了。就像我缺少IPreConfigureOptions之类。

public class PluginManager
{
    private readonly IOptions<ApplicationSettings> _settings;

    public PluginManager(IOptions<ApplicationSettings> settings)
    {
        _settings = settings;
        // how do i get an instance here which makes sure that the ApplicationSettings.PluginPaths is already manipulated without doing it manually?
    }
}

这样做是可行的，但是然后感觉就像我在与框架作斗争，因为我不能像其他地方一样使用IOptions<AppSettings>：

Answer 1

确认。我通过浏览一些Microsoft组件资源发现了它。

这是解决方案：

public class ApplicationSettingsSetup : IConfigureOptions<ApplicationSettings>
{
    private readonly IWildcardResolver _wildcardResolver;

    public ApplicationSettingsSetup(IWildcardResolver wildcardResolver)
    {
        _wildcardResolver = wildcardResolver;
    }

    /// <inheritdoc />
    public void Configure(ApplicationSettings options)
    {
        options.PluginFolders = _wildcardResolver.Resolve(options.PluginFolders);
    }
}

注册：

services.AddTransient<IConfigureOptions<ApplicationSettings>, ApplicationSettingsSetup>();
services.Configure<ApplicationSettings>(Configuration.GetSection("ApplicationSettings"));

[以前，我是从配置中加载AppSettings的，之后再注册IConfigurationOptions。我以某种方式假设创建Option的工厂会在返回IOptions实例之前先调用IConfigureOptions-这是错误的。

更改订单已解决。

Answer 2

这看起来更符合您要实现的目标

services.AddOptions<ApplicationSettings>()
    .Configure<IWildcardResolver>((options, wildcardResolver) => {
        options.PluginFolders = wildcardResolver.Resolve(options.PluginFolders);
        //...
    });

上面注册了一个用于配置特定类型选项的操作。注意：它们先运行。

参考Use DI services to configure options