可以只讀的 ServiceCollection

Intro

在 .NET 7 Preview 4 中，ServiceCollection 可以聲明為只讀了，這使得我們可以有效避免在構(gòu)建了 ServiceProvider 之后再新增服務(wù)，導(dǎo)致服務(wù)注冊失敗。

Sample

在新的版本中，ServiceCollection 新增了一個(gè) MakeReadonly() 的 API，調(diào)用之后，ServiceCollection 就不能再修改了，不能再注冊新的服務(wù)或者移除集合中的服務(wù)，再修改就會(huì)拋異常。

直接來看一個(gè)示例吧，示例代碼如下：

var?services?=?new?ServiceCollection();
services.AddSingleton();
await?using?(var?provider?=?services.BuildServiceProvider())
{
????Console.WriteLine(provider.GetRequiredService().GetHashCode());
}

Console.WriteLine(services.IsReadOnly);

services.MakeReadOnly();

Console.WriteLine(services.IsReadOnly);

try
{
????services.AddSingleton();
}
catch?(Exception?ex)
{
????Console.WriteLine(ex);
}

輸出結(jié)果如下：

43942917
False
True
System.InvalidOperationException:?The?service?collection?cannot?be?modified?because?it?is?read-only.
???at?Microsoft.Extensions.DependencyInjection.ServiceCollection.ThrowReadOnlyException()
???at?Microsoft.Extensions.DependencyInjection.ServiceCollection.CheckReadOnly()
???at?Microsoft.Extensions.DependencyInjection.ServiceCollection.System.Collections.Generic.ICollection.Add(ServiceDescriptor?item)
???at?Microsoft.Extensions.DependencyInjection.ServiceCollectionServiceExtensions.Add(IServiceCollection?collection,?Type?serviceType,?Type?implementationType,?ServiceLifetime?lifetime)
???at?Microsoft.Extensions.DependencyInjection.ServiceCollectionServiceExtensions.AddSingleton(IServiceCollection?services,?Type?serviceType,?Type?implementationType)
???at?Microsoft.Extensions.DependencyInjection.ServiceCollectionServiceExtensions.AddSingleton[TService,TImplementation](IServiceCollection?services)
???at?Net7Sample.ServiceCollectionSample.MainTest()?in?C:\projects\sources\SamplesInPractice\net7Sample\Net7Sample\ServiceCollectionSample.cs:line?28

More

在新的 HostApplicationBuilder 中也借助了這個(gè) API ，在構(gòu)建 Host 的時(shí)候也會(huì)調(diào)用這個(gè) API 來使得 ServiceCollection 中注冊的服務(wù)不能再變更，可以參考：https://github.com/dotnet/runtime/pull/68051/files#diff-e55c31d683c37cca99b7a3a274beef4a3101d53b02c9ea989e4f6310094f68ec

在我們的應(yīng)用中遇到想要使 ServiceCollection 不能再修改的時(shí)候就可以考慮使用這個(gè) API 來避免誤操作從而導(dǎo)致意外的 BUG

References

• https://github.com/dotnet/runtime/pull/68051
• https://github.com/dotnet/runtime/pull/68051/files#diff-e55c31d683c37cca99b7a3a274beef4a3101d53b02c9ea989e4f6310094f68ec
• https://github.com/dotnet/runtime/issues/66126
• https://github.com/WeihanLi/SamplesInPractice/blob/master/net7Sample/Net7Sample/ServiceCollectionSample.cs
• .NET 7 中的 HostApplicationBuilder