处理 "object reference not set to an instance of an object" 错误

Question

我收到错误消息：

System.NullReferenceException occurred HResult=-2147467261 Message=Object reference not set to an instance of an object when attempting to access a view.

错误指向这一行：

<span>@(d.AcceptPropagation == null ? string.Empty : "Accepts Propagation")</span>

我在 foreach 循环中设置了一个断点，然后逐步查找出现 null 的位置。直到第 5 次通过循环我才收到错误，并且我在 DocumentTemplate 处得到一个空值。我以为我正在正确处理 null。我需要额外的空检查吗？我需要以不同的方式处理吗？下面是视图。我还在代码中将“”更改为string.Empty。

@if (criteria != null)
        {
            foreach (var d in criteria)
            {
                <tr>
                    <td style="width: 80px;">
                        <a class="blue button edit-template" data-reveal-id="edit-form" id="@d.ID">Edit</a>
                    </td>
                    <td>
                        <strong>@(d.DocumentTemplate == null ? string.Empty: d.DocumentTemplate.Name)</strong><br />
                        <div>@d.GroupCode</div>
                        <span>@d.PlanCode</span>
                        <span>@d.SubPlanCode</span>
                        <span>@d.ActionCode</span>
                        <span>@d.AdmitTerm</span>
                        <span>@d.AdmitTypeCode</span>
                        <span>@d.ProgramCode</span>
                        <span>@d.ResidentCode</span>
                        <span>@(d.V19 == true ? "V19" : string.Empty)</span>
                        <span>@(d.A23 == true ? "A23" : string.Empty)</span>
                        <span>@(d.AcceptPropagation == null ? string.Empty : "Accepts Propagation")</span> 
                        <div><a href="@Url.Content(d.DocumentTemplate.Path)">@(Url.Content(d.DocumentTemplate.Path)==null? string.Empty : d.DocumentTemplate.Path)</a></div>
                    </td>
                </tr>
            }
        }

Answer 1

您没有检查此行中的 DocumentTemplate 是否为 null

<div><a href="@Url.Content(d.DocumentTemplate.Path)">@(Url.Content(d.DocumentTemplate.Path)==null? string.Empty : d.DocumentTemplate.Path)</a></div>

Answer 2

实际上是您提到的导致问题的行下方的行。由于某种原因，Razor 视图 NullReferenceExceptions 多次指向上面的行。将其下面的行更改为具有相同的空检查，它将起作用：

<div>
    @if(d.DocumentTemplate != null)
    {
        <a href="@Url.Content(d.DocumentTemplate.Path)">@d.DocumentTemplate.Path</a>    
    }
</div>

查看 this link 用户最初发现问题的位置。

处理 "object reference not set to an instance of an object" 错误

Handle "object reference not set to an instance of an object" error

asp.net-mvc

entity-framework

.net-4.0