值不能为空。参数名称：尝试使用 web api 获取数据时的源
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【中文标题】值不能为空。参数名称：尝试使用 web api 获取数据时的源【英文标题】：Value cannot be null. Parameter name: source when trying to get data with web api 【发布时间】：2020-08-26 17:42:09 【问题描述】：我有这个问题，我整晚都在尝试解决这个问题，我为此绞尽脑汁，对不起，如果这很愚蠢，我是一个相对较新的程序员..
它应该通过 Web API 从我的数据库中获取一些数据，并将其显示在数据网格中（使用 blazorise 的数据网格），但它不起作用..
代码：
@using Newtonsoft.Json;
@page "/email/inbox"
<Row>
<Column>
<Card Margin="Margin.Is4.OnY">
<CardHeader>
<CardTitle>Data Grid</CardTitle>
</CardHeader>
<CardBody>
<CardText>Combine diferent datagrid options</CardText>
</CardBody>
<CardBody>
<DataGrid TItem="Fornecedor"
Data="@dataModels"
EditMode="DataGridEditMode.Popup"
Editable="true"
Sortable="true"
Filterable="true"
ShowPager="true"
RowInserted="@OnRowInserted"
RowUpdated="@OnRowUpdated"
RowRemoved="@OnRowRemoved"
UseInternalEditing="true"
@bind-SelectedRow="@fornecedorSelecionado"
Striped="true"
Bordered="true"
Hoverable="true"
CustomFilter="@OnCustomFilter">
<DataGridAggregates>
<DataGridAggregate TItem="Fornecedor" Field="@nameof( Fornecedor.Email )" Aggregate="DataGridAggregateType.Count">
<DisplayTemplate>
@($"Total emails: context.Value")
</DisplayTemplate>
</DataGridAggregate>
<DataGridAggregate TItem="Fornecedor" Field="@nameof( Fornecedor.Validado )" Aggregate="DataGridAggregateType.TrueCount" />
</DataGridAggregates>
<DataGridColumns>
<DataGridCommandColumn TItem="Fornecedor" Width="170px">
<NewCommandTemplate>
<Button Color="Color.Success" Clicked="@context.Clicked">New</Button>
</NewCommandTemplate>
<EditCommandTemplate>
<Button Color="Color.Primary" Clicked="@context.Clicked">Edit</Button>
</EditCommandTemplate>
<SaveCommandTemplate>
<Button Color="Color.Primary" Clicked="@context.Clicked">Save</Button>
</SaveCommandTemplate>
<DeleteCommandTemplate>
<Button Color="Color.Danger" Clicked="@context.Clicked">Delete</Button>
</DeleteCommandTemplate>
<CancelCommandTemplate>
<Button Color="Color.Secondary" Clicked="@context.Clicked">Cancel</Button>
</CancelCommandTemplate>
<ClearFilterCommandTemplate>
<Button Color="Color.Warning" Clicked="@context.Clicked">Clear Filter</Button>
</ClearFilterCommandTemplate>
</DataGridCommandColumn>
<DataGridColumn TItem="Fornecedor" Field="@nameof( Fornecedor.Id )" Caption="#" Sortable="false" Width="60px" />
<DataGridColumn TItem="Fornecedor" Field="@nameof( Fornecedor.NomeEmpresa )" Caption="Fornecedor" Editable="true">
<FilterTemplate>
<TextEdit Placeholder="Search name" TextChanged="@(v=>context.TriggerFilterChange(v))" />
</FilterTemplate>
</DataGridColumn>
<DataGridColumn TItem="Fornecedor" Field="@nameof( Fornecedor.NomeContato )" Caption="Contato" Editable="true" />
<DataGridDateColumn TItem="Fornecedor" Field="@nameof( Fornecedor.Telefone )" DisplayFormat="(00)00000-0000" Caption="Telefone" Editable="true" />
<DataGridColumn TItem="Fornecedor" Field="@nameof( Fornecedor.Email )" Caption="Email" Editable="true" />
<DataGridColumn TItem="Fornecedor" Field="@nameof( Fornecedor.CEP )" Caption="CEP" Editable="true" />
<DataGridColumn TItem="Fornecedor" Field="@nameof( Fornecedor.Cidade )" Caption="Cidade" Editable="true">
<FilterTemplate>
<Select TValue="string" SelectedValueChanged="@(e => context.TriggerFilterChange(e == "*" ? "" : e.ToString()))">
<SelectItem Value="@("*")">All</SelectItem>
@foreach (var item in dataModels)
<SelectItem Value="@item.Cidade">@item.Cidade</SelectItem>
</Select>
</FilterTemplate>
</DataGridColumn>
<DataGridColumn TItem="Fornecedor" Field="@nameof( Fornecedor.Endereco )" Caption="Endereço" Editable="true" Filterable="false" />
<DataGridColumn TItem="Fornecedor" Field="@nameof( Fornecedor.Servico )" Caption="Serviço" Editable="true" />
<DataGridColumn TItem="Fornecedor" Field="@nameof( Fornecedor.Especialidade )" Caption="Especialidades" Editable="true" />
<DataGridCheckColumn TItem="Fornecedor" Field="@nameof(Fornecedor.Validado)" Caption="Validado" Editable="true" Filterable="false">
<DisplayTemplate>
<Check TValue="bool?" Checked="context.Validado" Disabled="true" ReadOnly="true" />
</DisplayTemplate>
</DataGridCheckColumn>
</DataGridColumns>
</DataGrid>
</CardBody>
</Card>
</Column>
</Row>
<Row>
<Column>
<Card>
<CardHeader>
<CardTitle>Fornecedor Selecionado</CardTitle>
</CardHeader>
<CardBody>
<Fields>
<Field>
<FieldLabel>Fornecedor</FieldLabel>
<FieldBody>
<TextEdit ReadOnly="true" Text="@fornecedorSelecionado?.NomeEmpresa"></TextEdit>
</FieldBody>
</Field>
<Field>
<FieldLabel>Contato</FieldLabel>
<TextEdit ReadOnly="true" Text="@fornecedorSelecionado?.NomeContato"></TextEdit>
</Field>
</Fields>
<Fields>
<Field>
<FieldLabel>Telefone</FieldLabel>
<FieldBody>
<NumericEdit TValue="int" ReadOnly="true" Text="@fornecedorSelecionado?.Telefone"></NumericEdit>
</FieldBody>
</Field>
<Field>
<FieldLabel>Email</FieldLabel>
<TextEdit ReadOnly="true" Text="@fornecedorSelecionado?.Email"></TextEdit>
</Field>
</Fields>
</CardBody>
</Card>
</Column>
</Row>
@code
public class DataService
HttpClient client = new HttpClient();
public async Task<List<Fornecedor>> GetUsuariosAsync()
try
string url = "https://myAPI.azurewebsites.net/Api/Fornecedores";
var response = await client.GetStringAsync(url);
var fornecedores = JsonConvert.DeserializeObject<List<Fornecedor>>(response);
return fornecedores;
catch (Exception ex)
throw ex;
DataGridEditMode editMode = DataGridEditMode.Popup;
bool editable = true;
bool sortable = true;
bool filterable = true;
bool showPager = true;
Fornecedor fornecedorSelecionado;
public class Fornecedor
public int Id get; set;
public string NomeEmpresa get; set;
public string NomeContato get; set;
public int Telefone get; set;
public string Email get; set;
public int CEP get; set;
public string Cidade get; set;
public string Endereco get; set;
public string Servico get; set;
public string Especialidade get; set;
public string Especialidade_dois get; set;
public string Especialidade_tres get; set;
public string Website get; set;
public bool? Validado get; set;
DataService dataService;
protected async Task FornecedoresAPI()
try
await dataService.GetUsuariosAsync();
catch (Exception ex)
throw ex;
List<Fornecedor> dataModels;
// generated with https://mockaroo.com/
protected override async Task OnInitializedAsync()
dataService = new DataService();
dataModels = await dataService.GetUsuariosAsync();
string customFilterValue;
bool OnCustomFilter(Fornecedor model)
if (string.IsNullOrEmpty(customFilterValue))
return true;
return
model.NomeEmpresa?.Contains(customFilterValue, StringComparison.OrdinalIgnoreCase) == true
|| model.NomeContato?.Contains(customFilterValue, StringComparison.OrdinalIgnoreCase) == true
|| model.Email?.Contains(customFilterValue, StringComparison.OrdinalIgnoreCase) == true;
我收到此错误：
ArgumentNullException：值不能为空。 （参数'来源'）
System.Linq.ThrowHelper.ThrowArgumentNullException（ExceptionArgument 参数） System.Linq.Enumerable.Count(IEnumerable 源，Func 谓词) Blazorise.DataGrid._DataGridAggregateRow.CountOf(DataGridColumn 列) Blazorise.DataGrid._DataGridAggregateRow.Calculate（DataGridAggregate 列） Blazorise.DataGrid._DataGridAggregateRow+c__DisplayClass32_0.b__1(RenderTreeBuilder __builder3) Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddContent（int 序列，RenderFragment 片段） Blazorise.TableRowCell.BuildRenderTree(RenderTreeBuilder __builder) Microsoft.AspNetCore.Components.ComponentBase.<.ctor>b__6_0（RenderTreeBuilder 构建器） Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch（RenderBatchBuilder batchBuilder，RenderFragment renderFragment） Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry) Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue() Microsoft.AspNetCore.Components.Rendering.htmlRenderer.HandleException（异常异常） Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue() Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessPendingRender() Microsoft.AspNetCore.Components.RenderTree.Renderer.AddToRenderQueue（int componentId，RenderFragment renderFragment） Microsoft.AspNetCore.Components.RenderHandle.Render(RenderFragment renderFragment) Microsoft.AspNetCore.Components.ComponentBase.StateHasChanged() Microsoft.AspNetCore.Components.ComponentBase.CallOnParametersSetAsync() Microsoft.AspNetCore.Components.ComponentBase.RunInitAndSetParametersAsync() Microsoft.AspNetCore.Components.Rendering.HtmlRenderer.HandleException（异常异常） Microsoft.AspNetCore.Components.RenderTree.Renderer.AddToPendingTasks（任务任务） Microsoft.AspNetCore.Components.Rendering.ComponentState.SetDirectParameters（ParameterView 参数） Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderRootComponentAsync(int componentId, ParameterView initialParameters) Microsoft.AspNetCore.Components.Rendering.HtmlRenderer.CreateInitialRenderAsync（类型 componentType，ParameterView 初始参数） Microsoft.AspNetCore.Components.Rendering.HtmlRenderer.RenderComponentAsync（类型 componentType，ParameterView 初始参数） Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext+c__11+
d.MoveNext() Microsoft.AspNetCore.Mvc.ViewFeatures.StaticComponentRenderer.PrerenderComponentAsync（ParameterView参数，HttpContext httpContext，类型componentType） Microsoft.AspNetCore.Mvc.ViewFeatures.ComponentRenderer.PrerenderedServerComponentAsync(HttpContext context, ServerComponentInvocationSequence invocationId, Type type, ParameterView parametersCollection) Microsoft.AspNetCore.Mvc.ViewFeatures.ComponentRenderer.RenderComponentAsync(ViewContext viewContext, Type componentType, RenderMode renderMode, object parameters) Microsoft.AspNetCore.Mvc.TagHelpers.ComponentTagHelper.ProcessAsync（TagHelperContext 上下文，TagHelperOutput 输出） Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner.g__Awaited|0_0（任务任务，TagHelperExecutionContext executionContext，int i，int count） _Host.cshtml 中的 Revvi.Pages.Pages__Host.b__14_1() + Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperExecutionContext.SetOutputContentAsync() _Host.cshtml 中的 Revvi.Pages.Pages__Host.ExecuteAsync() + 布局=空； Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync（IRazorPage 页面，ViewContext 上下文） Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync（IRazorPage 页面，ViewContext 上下文，bool invokeViewStarts） Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync（ViewContext 上下文） Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, string contentType, Nullable statusCode) Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, string contentType, Nullable statusCode) Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|29_0（ResourceInvoker 调用者，Task lastTask，State next，Scope 范围，对象状态，bool isCompleted） Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow（ResultExecutedContextSealed 上下文） Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext(ref State next, ref Scope scope, ref object state, ref bool isCompleted) Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters() Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|24_0（ResourceInvoker 调用者，Task lastTask，State next，Scope 范围，对象状态，bool isCompleted） Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow（ResourceExecutedContextSealed 上下文） Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(ref State next, ref Scope scope, ref object state, ref bool isCompleted) Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync() Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0（ResourceInvoker 调用程序，任务任务，IDisposable 范围） Microsoft.AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|6_0（端点端点、任务 requestTask、ILogger 记录器） Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
我完全不知道该怎么做..
【问题讨论】：
您是否确保您的dataModels 数据源不为空且不包含任何空记录？
如我所见，您正在获取您的dataModels async。确保在完全获取它之前没有渲染与此 dataModels 相关的任何内容。在 Task<> 完成之前，它只是 null。
【参考方案1】：
您的 List<Fornecedor> dataModels; 最初是 null。
要么将其初始化为一个空列表，
List<Fornecedor> dataModels = new List<Fornecedor> ();
或将大部分剃须刀代码包装在@if (dataModels != null) ...
以 FetchData 模板页面为例。
Blazorise.DataGrid 可能确实知道如何处理 null 集合，我希望它知道。但是您在“Cidade”列的过滤器中也有 foreach() 循环，看起来这会引发异常。
【讨论】：
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