ASP.NET Core使用ViewAsPdf导出PDF时ViewBag值不显示问题咨询

1. 核心原因是Rotativa.AspNetCore的ViewAsPdf实例不会自动继承当前控制器上下文的ViewBag/ViewData数据，直接返回新建的ViewAsPdf对象时，视图渲染时拿到的是空的ViewData集合，而ViewBag本质是ViewData的动态包装器，因此视图中读取的ViewBag内容全部为空。
2. 额外可排查点：可先在控制器方法入口打断点，确认请求传入的UserName和ActivityName参数是否正常接收，若参数本身为空，后续赋值的ViewBag也会是空值。
3. 视图代码未使用ViewBag.ActivityName，就算ViewBag传值成功，活动名称也不会在PDF中展示。

方案1：手动传入ViewData（适配你当前用ViewBag的写法） #

修改控制器代码，给ViewAsPdf的ViewData属性赋值为当前控制器的ViewData即可，修改后的代码如下：

public IActionResult PrintCertification(String UserName , String ActivityName )
{
    ViewBag.UserName = UserName;
    ViewBag.ActivityName = ActivityName;
    return new ViewAsPdf("PrintCertification")
    {
        PageOrientation = Rotativa.AspNetCore.Options.Orientation.Landscape,
        // 手动传入当前控制器的ViewData，即可把ViewBag内容带到视图中
        ViewData = ViewData
    };
}

同时修改视图代码，把需要动态展示活动名的位置替换成@ViewBag.ActivityName，示例如下：

<h3 id="content">
    For his valuable participation as ( a leader/an organizer) in the (campaign/ activity/ course) of <br>@ViewBag.ActivityName, that aims to ( aim of the activity).<br>
    Targeting (target audience).<br>
    Held in ( place), On (Date).
</h3>

方案2：改用强类型ViewModel传参（更规范，避免动态类型拼写错误） #

1. 先定义视图模型类

public class CertificationViewModel
{
    public string UserName { get; set; }
    public string ActivityName { get; set; }
    // 其他需要动态填充的字段均可在此定义
}

2. 修改控制器代码，直接把模型传给ViewAsPdf

public IActionResult PrintCertification(string UserName , string ActivityName )
{
    var model = new CertificationViewModel
    {
        UserName = UserName,
        ActivityName = ActivityName
    };
    return new ViewAsPdf("PrintCertification", model)
    {
        PageOrientation = Rotativa.AspNetCore.Options.Orientation.Landscape
    };
}

3. 修改视图代码，声明模型后取值

@model CertificationViewModel
<html>
<head>
    <h1 id="CA" style="align-content:center">Certificate of Apperciation</h1>
</head>
<body  class="bg" style="background-image: url(https://localhost:44387/Screenshot.png); ">
    <h3 id="TC">The College of Medicine at King Faisal University would like to thank</h3>
    <h1 id="name">@Model.UserName</h1>
    <h3 id="content">
        For his valuable participation as ( a leader/an organizer) in the (campaign/ activity/ course) of <br>@Model.ActivityName, that aims to ( aim of the activity).<br>
        Targeting (target audience).<br>
        Held in ( place), On (Date).
    </h3>
    <h4 id="Dr">Dr. Naif Mohammed Alhmam</h4>
    <h4 id="OS">Official Seal</h4>
    <h4 id="VD">Vice-dean for development <br>and community partnership</h4>
</body>
</html>

你当前视图中背景图用的是localhost本地地址，部署到生产环境后会无法加载，建议将图片转为base64编码嵌入视图，或者替换为服务器的公网绝对地址。

内容的提问来源于stack exchange，提问作者abdulelah alasfour