初始化静态 class 的属性失败，出现空值异常

Question

我有一个静态连接工厂class，需要从配置中初始化连接参数

namespace MyApp.Common.LinqToDB
{
    public static class MyConnectionFactory
    {
        public static string Authority { get; set; }
        public static string Target { get; set; }
        public static string ConnectionString { get; set; }
        public static string ClientId { get; set; }
        public static string ClientSecret { get; set; }
        private static ClientCredential ClientCredential = new ClientCredential(ClientId, ClientSecret);

    public static IDbConnection createConnection()
        {
            AuthenticationContext authenticationContext = new AuthenticationContext(Authority);
            AuthenticationResult authenticationResult = authenticationContext.AcquireTokenAsync(Target, ClientCredential).Result;
            SqlConnection MyDataConnection = new SqlConnection(ConnectionString);
            MyDataConnection.AccessToken = authenticationResult.AccessToken;

            return MyDataConnection;
        }
    }
}

我尝试在主程序中初始化这些属性

MyConnectionFactory.Authority = "blahblah";

这会在静态 class 中引发空值异常。该值没有到达 class.

System.TypeInitializationException
  HResult=0x80131534
  Message=The type initializer for 'Workspace.Common.LinqToDB.WorkspaceConnectionFactory' threw an exception.
  Source=Common
  StackTrace:
   at Workspace.Common.LinqToDB.WorkspaceConnectionFactory.set_Authority(String value) in 

........
Inner Exception 1:
ArgumentNullException: Value cannot be null.
Parameter name: clientId

设置静态属性的值是否错误class。我知道 static constructor() 但它不带参数，我需要设置连接参数。静态工厂不是连接工厂的正确模式吗？如果我不使工厂静态化，我可以使整个事情正常进行，但这似乎不是正确的做法。

Answer 1

private static ClientCredential ClientCredential = new ClientCredential(ClientId, ClientSecret); 将编译为：

private static ClientCredential ClientCredential;

//Static constructor
static MyConnectionFactory()
{
  ClientCredential = new ClientCredential(ClientId, ClientSecret);
}

A static constructor is used to initialize any static data, or to perform a particular action that needs to be performed once only. It is called automatically before the first instance is created or any static members are referenced.
https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/static-constructors

现在，当您尝试分配 Authority 时，必须先调用静态构造函数。此时，ClientId 和 ClientSecret 仍然为空，这导致了异常。

初始化静态 class 的属性失败，出现空值异常

Initializing properties of static class fails with null value exception

c#

initialization

static-classes