ServiceCollection services = new ServiceCollection();//定义一个承放服务的集合
services.AddScoped<iGetRole, GetRole>();

using (ServiceProvider serviceProvider = services.BuildServiceProvider())
{

    var list = serviceProvider.GetServices(typeof(iGetRole));
    //获取到所有注册iGetRole类的实现对象

    foreach (var item in list)
    {

    }

}

    var list = serviceProvider.GetServices(typeof(iGetRole));//如果获取不到 则返回null
    var t = serviceProvider.GetRequiredService<iGetRole>();//如果获取不到 则抛出异常

DI注入方式

默认：构造函数注入；属性注入；

---------------------------------------------------------------------------------------------------------------------------------

自动注入示例：

public class MailKitService : IMailKitService
{
    private readonly ILogService _logService;
    private readonly IConfigService _configService;


    public MailKitService(ILogService _logService, IConfigService _configService)
    {
        this._logService = _logService;
        this._configService = _configService;

    }

    public void SendMail(string address, string copyAddress, string title, string content)
    {

        _logService.LogInfo($"发送地址：{address}");

        throw new NotImplementedException();
    }
}


ServiceCollection services = new ServiceCollection();

services.AddScoped<IConfigService, ConfigService>();
services.AddScoped<ILogService, LogService>();
services.AddScoped<IMailKitService, MailKitService>();


using (var provider = services.BuildServiceProvider())
{
    var mailService = provider.GetRequiredService<IMailKitService>();
    //实现IMailKitService服务的 MailKitService构造函数会自动被注入ConfigService、LogService值
    

    mailService.SendMail("11","","","");

}

---------------------------------------------------------------------------------------------------------------------------------

自定义扩展方法，与扩展对象同命名空间，使用this,使用地方可以直接点出来。（必须是静态类）