当我发布public void时OnPost（）不触发？
实际上，它不会触发，因为你已经绑定了表单与强类型模型，这是@Model.Employee.ID，所以当你发送请求，它没有找到匹配的模型，你没有得到任何东西。你应该在页面上定义你的模型，这将解决你的问题。
正确的方法应该如下：

cshtml.cs：

public class EmployeeModel : PageModel
{
    public Employee? Employee { get; set; }
    public void OnGet()
    {
        Employee = new Employee();
        Employee.ID = 1;
        Employee.FirstName = "Test First Name";
        Employee.Email = "TestEmail@email.com";
        Employee.Mobile = "0123456789";
    }
    public void OnPost()
    {
        Employee = new Employee();
        Employee.ID = Convert.ToInt32(Request.Form["ID"].ToString());
        Employee.FirstName = Request.Form["FirstName"].ToString();
        Employee.Email = Request.Form["Email"].ToString();
        Employee.Mobile = Request.Form["Mobile"].ToString();
    }
}

型号：

public class Employee
    {
        public int ID { get; set; }
        public string FirstName { get; set; }
        public string Email { get; set; }
        public string Mobile { get; set; }
    }

cshtml：

@page
@model RazorPageDemoApp.Pages.EmployeeModel

<form method="post">
    <input type="text" style="display:none;" name="Id"
           value="@Model.Employee.ID" />
    <div class="form-group">
        <label for="name">Name</label>
        <input type="text" class="form-control" value="@Model.Employee.FirstName"
               name="FirstName" id="FirstName" placeholder="Enter Name">
    </div>
    <br />
    <div class="form-group">
        <label for="email">Email address</label>
        <input type="email" class="form-control" value="@Model.Employee.Email"
               name="email" id="email" aria-describedby="emailHelp"
               placeholder="Enter email">
    </div>
    <br />
    <div class="form-group">
        <label for="email">Mobile</label>
        <input type="text" class="form-control" value="@Model.Employee.Mobile"
               name="mobile" id="mobile" aria-describedby="emailHelp"
               placeholder="Enter email">
    </div>
    <br />

    <button type="submit" class="btn btn-primary">A</button>
</form>

输出：

**注：**如果您想了解更多关于Razor Page Form提交的详细信息，您可以在这里查看我们的官方文件。