如何通过将viewbag对象转换为asp.net mvc中的列表来在html表中显示viewbag数据

Question

我从控制器传递 viewbag 中的列表数据。访问 viewbag 作为列表时出现错误。

error - 'Object reference not set to an instance of an object.'

在这一行出现错误。 ViewBag.Total_PowerList as IEnumerable<TransformerEnergyMonitoring.Models.KWHConsumption>

查看

@model IEnumerable<TransformerEnergyMonitoring.Models.KWHConsumption>
    <div class="row">
     
            <div class="table-responsive">
                <table id="myTable" class="table table-bordered table-hover table-striped">
                    <thead class="table-header">
                        <tr>
                            <th>Date</th>
                            <th>KWH Reading</th>
                            <th>KWH Consumption</th>
                        </tr>
                    </thead>
                    <tbody>
                            @foreach (var item in (ViewBag.Total_PowerList as IEnumerable<TransformerEnergyMonitoring.Models.KWHConsumption>))
                            {
                                <tr>
                                    <td>@item.timeStamp</td>
                                </tr>
                            }
                    </tbody>
                </table>
            </div>
    </div>

数据集

{ timeStamp = 12/5/2020 12:00:00 AM, finalState = 47326.95, consuption = 1455.71 }

控制器

public ActionResult KWHDateWise(RangeSelection RS)
    {
        DateTime ToDate = Convert.ToDateTime(RS.ToDate).AddDays(1);
        RS.ToDate = ToDate;

        List<KWHConsumption> kwhcon = new List<KWHConsumption>();
        
      var Total_PowerList = db.Total_Power.Where(u => u.DeviceImei == RS.DeviceImei && (u.DeviceTimeStamp >= RS.FromDate && u.DeviceTimeStamp <= RS.ToDate)).OrderByDescending(u => u.DeviceTimeStamp).ToList();

        ViewBag.Total_PowerList= Total_PowerList
.GroupBy(
    i => i.DeviceTimeStamp.Date,
    (timeStamp, dayilyData) => new { timeStamp, dayilyData })
.Select(i => new
{
    i.timeStamp,
    finalState = i.dayilyData.Max(x => x.KWH),
    consuption = (i.dayilyData.Max(x => x.KWH) - i.dayilyData.Min(x => x.KWH))
})
.ToList();
        return PartialView("~/Views/TransEnergyHistory/_KWH.cshtml", kwhcon);
    }

型号

 public class KWHConsumption
    {
       
        public DateTime timeStamp { get; set; }
        public double finalState { get; set; }
        public double consuption { get; set; }

    }

Answer 1

当您使用 viewbag 时，它是一个不关心内部数据类型的动态结构，您应该做的是将数据类型转换为您想要的类型，这里有一个示例：

提供了这个TestModel

public class TestModel
{
    public string Id { get; set; }
    public int Number { get; set; }
    public string Name { get; set; }
}

和控制器中的这个动作

    public IActionResult Index()
    {
        var vm = new List<TestModel>() {
            new TestModel(){
                Id = "randomId1",
                Name = "randomName1",
                Number = 2
            },
            new TestModel(){
                Id = "randomId2",
                Name = "randomName2",
                Number = 1
            },
            new TestModel(){
                Id = "randomId3",
                Name = "randomName3",
                Number = 3
            },
        };
        ViewBag.TestModels = vm;
        return View();
    }

在你看来应该是这样的

@foreach (var item in (ViewBag.TestModels as IEnumerable<TestModel>))
{
  <tr>
    <td>@item.Id</td>
    <td>@item.Number</td>
    <td>@item.Name</td>
  </tr>
}

我假设在你的情况下你想要的方式是

(ViewBag.Total_PowerList as IEnumerable<TransformerEnergyMonitoring.Models.Total_Power>)