将Swagger添加到ASP.Net Core Web API

我正在尝试将Swagger添加到我的ASP.Net Core Web API项目中，如下所示：

public void ConfigureServices(IServiceCollection services)
{
       services.AddControllers();
       services.AddSwaggerGen(c =>
       {
          c.SwaggerDoc("v0.1", new OpenApiInfo { Title = "My API", Version = "v0.1" });
       });
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            ...
            app.UseHttpsRedirection();

            app.UseSwagger();
            app.UseSwaggerUI(c =>
            {
                c.SwaggerEndpoint("/swagger/v0.1/swagger.json", "My API V1");
            });

            app.UseRouting();

            app.UseAuthorization();
            ...
}

但我收到此错误：

找不到类型或名称空间名称“ OpenApiInfo”

我已经安装了Swashbuckle.AspNetCore v4.0.1，我的项目是.Net Core 3.0。