用户点击搜索按钮后,我想显示一个包含信息字段的列表,除了Image之外,一切都很好。我有一个ActionResult方法,从视图中获取Id并在点击事件中向用户显示图像。
到目前为止的问题是在控制器中,即使'item.Image.ImageId'有一个Id值,左边的部分(我发送给视图的模型),抛出Null Reference Exception,所以我无法传递Image Id使用'href =“〜/ Process /..."'
查看视图屏幕截图错误:Object reference not set to an instance of an object.
我的控制器:
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Index(SearchModel FormModel)
{
int districtNo = Convert.ToInt32(FormModel.DistrictNo);
List<SearchModel> ResultsList = new List<SearchModel>();
IQueryable<LetterInfo> DbQueries = // Get result from db
foreach (var item in DbQueries.ToList())
{
FormModel.FirstName = item.FirstName;
FormModel.LastName = item.LastName;
...
FormModel.Image.ImageId = item.Image.ImageId;
// FromModel.Image.ImageId - null reference exception
ResultsList.Add(FormModel);
}
ViewBag.ResultsToView = ResultsList;
}
return View(new SearchModel());
}
SearchModel类:
public class SearchModel
{
.
.
.
public Image Image { get; set; }
}
LetterInfo课程:
public class LetterInfo
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int LetterId { get; set; }
.
.
.
public virtual Image Image { get; set; }
}
返回图像文件的方法:
public ActionResult ViewImage(int Id)
{
var img = db.Images.First(a => a.ImageId == Id);
var stream = new MemoryStream(img.FileContents);
var lname = "letter" + Path.GetExtension(img.FileName)?.ToLower();
Response.AppendHeader("Content-Disposition", $"inline; filename={lname}");
return File(stream, Helpers.GetMimeType(img.FileName));
}
查看:
@model SearchModel
@section scripts{
<script type="text/javascript">
var win;
$('#openImage').click(function (event) {
event.preventDefault();
win = window.open(this.href, 'child', 'resizable=1');
return false;
});
</script>
}
...
@foreach (var item in ModelList){
<li></li>
...
<li class="list-group-item">
<a href="~/Process/ViewImage/@item.Image.ImageId" id="openImage">
<!-- On click open image file -->
<span>Click to see image</span>
</a>
</li>
}
答案 0 :(得分:0)
FormModel.Image
或item.Image
为空。 NullReferenceException
是一个运行时错误,当您根据其类型访问某个特定对象 所拥有的成员时发生,但实际上由于该实例为null而没有,并且例如,null没有ImageId
之类的属性。