ASP.NET Core 8 Blazor Server获取连接字符串报错：找不到合适构造函数

尝试多种方法均无法从appsettings.json中获取连接字符串，当前方案运行时抛出以下错误，求可行解决方案：

System.InvalidOperationException: A suitable constructor for type 'App.Services.DataService' could not be located. Ensure the type is concrete and all parameters of a public constructor are either registered as services or passed as arguments. Also ensure no extraneous arguments are provided.

现有代码 #

appsettings.json #

{
    "ConnectionStrings": {
        "Database1": "Server=_____.____.____;Database=______;Trusted_Connection=True;MultipleActiveResultSets=true;"
    }
}

Program.cs #

builder.Services.Configure<ConnectionStrings>
              (builder.Configuration.GetSection("ConnectionStrings"));
builder.Services.AddSingleton<IDataService, DataService>();

ConnectionStrings.cs #

public class ConnectionStrings
{
    public string Database1 { get; set; }
}

DataService.cs #

public class DataService : IDataService
{
    private readonly ConnectionStrings _connectionStrings;

    public DataService(IOptions<ConnectionStrings> connectionStrings)
    {
        _connectionStrings = connectionStrings.Value;
    }
}

Page.razor #

@inject IDataService DataService 

...

_elements = await DataService.GetElementsByTerm(term);
...

可行解决方案 #

方案一：修复当前IOptions注入逻辑 #

现有代码逻辑本身是正确的，报错大概率是以下细节问题导致：

• 确认ConnectionStrings类所在的命名空间已被Program.cs引用
• 确认IDataService是public接口，且DataService完整实现了该接口的所有成员
• 检查ConnectionStrings类的属性名Database1与appsettings.json中的键名完全一致（大小写敏感）

如果以上都没问题，重新清理解决方案并重新生成，即可正常注入。

方案二：直接注入ConnectionStrings实例（简化版） #

无需通过IOptions包装，直接将配置实例注册为服务：

1. 修改Program.cs：

// 读取配置并转为ConnectionStrings实例
var connectionStrings = builder.Configuration.GetSection("ConnectionStrings").Get<ConnectionStrings>();
// 注册为单例服务
builder.Services.AddSingleton(connectionStrings);
// 保持DataService的注册不变
builder.Services.AddSingleton<IDataService, DataService>();

2. 修改DataService.cs的构造函数，直接注入ConnectionStrings：

public class DataService : IDataService
{
    private readonly ConnectionStrings _connectionStrings;

    public DataService(ConnectionStrings connectionStrings)
    {
        _connectionStrings = connectionStrings;
    }
}

方案三：直接注入单个连接字符串（更轻量化） #

如果只需要Database1这一个连接字符串，可以直接注册字符串：

1. 修改Program.cs：

var dbConnStr = builder.Configuration.GetConnectionString("Database1");
builder.Services.AddSingleton(dbConnStr);
builder.Services.AddSingleton<IDataService, DataService>();

2. 修改DataService.cs：

public class DataService : IDataService
{
    private readonly string _dbConnectionString;

    public DataService(string dbConnectionString)
    {
        _dbConnectionString = dbConnectionString;
    }
}

内容的提问来源于stack exchange，提问作者Jim