I have a Blazor component that handles scanning barcodes for a redelivery process. When I scan an item for the first time and select a reason, the corresponding card does not appear on the UI. However, if I scan the item again, the card shows up as expected. I want the card to show up immediately after the initial scan and reason selection.
Here is the relevant code for my Blazor component and ViewModel:
@page "/scanoffforredelivery"@namespace Parrot.Client.Razor.Controls.Components.Redelivery@using Parrot.Common.DataDefinitions.Custom.Redelivery@using Parrot.Common.DataDefinitions.Models.Redelivery@using static Parrot.Client.Razor.Controls.ViewModels.Invoicing.IScanOffForRedeliveryViewModel@inherits ParrotComponentBase<Spinner IsModal="true" IsLoading="@(VM.IsNull() || VM.IsBusy)" Caption="@(VM.BusyText ?? "")"><ContentTemplate><!-- Existing UI code --></ContentTemplate></Spinner>@code { protected override async Task OnInitializedAsync() { await base.OnInitializedAsync(); VM.OnUIUpdate = StateHasChanged; // Set the UI update callback VM.Setup(); }}View model
using Microsoft.AspNetCore.Components;using System;using System.Threading.Tasks;namespace Parrot.Client.Razor.Controls.ViewModels.Invoicing{ internal sealed class ScanOffForRedeliveryViewModel : ComponentViewModelBase, IScanOffForRedeliveryViewModel { private readonly IWebServiceProvider _webServiceProvider; public Action OnUIUpdate { get; set; } public ScanOffForRedeliveryViewModel(IWebServiceProvider webServiceProvider) { _webServiceProvider = webServiceProvider; } public async Task InsertRecordAsync() { var request = new ScannedRequest { Barcode = BarcodeInput.ToInt(), RedeliveryReason = SelectedReason }; var processResult = await _webServiceProvider.Of<IRedeliveryService>().InsertScannedItemAsync(request); if (processResult.IsNullOr(x => x.IsNotValid)) { SuccessResultBuilder sr = new SuccessResultBuilder(); sr.Invalid().WithError(processResult.AllMessagesToStringWithNoNumbers()); EmitResult(sr); return; } if (ShowRedeliveryReasonsModal) { ToggleRedeliveryReasonModal(); return; } UpdateDisplayAfterScan(processResult.Value); UpdateCompleteButtonState(); OnUIUpdate?.Invoke(); // Invoke the UI update callback } public async Task RetrieveBarcodeInfoAsync() { try { SetAsBusy("Loading Details..."); if (!IsValidBarcode(BarcodeInput)) { var sr = new SuccessResultBuilder(); sr.Invalid().WithError("Invalid barcode format"); EmitResult(sr); return; } var request = new ScannedRequest { Barcode = BarcodeInput.ToInt(), }; var scanResult = await _webServiceProvider.Of<IRedeliveryService>().ScanAsync(request); if (scanResult.IsNullOr(x => x.IsNotValid)) { SuccessResultBuilder sr = new SuccessResultBuilder(); sr.Invalid().WithError(scanResult.AllMessagesToStringWithNoNumbers()); EmitResult(sr); return; } var reasonResult = await CheckInvoiceInRedeliveryHeaderAsync(scanResult); if (reasonResult.IsNullOr(x => x.IsNotValid) && SelectedReason.IsNullOr(x => x.Id.HasNoValue())) { ToggleRedeliveryReasonModal(); return; } if (reasonResult.IsNotNullAnd(x => x.IsValid)) { SelectedReason = reasonResult.Value; } request.RedeliveryReason = SelectedReason; var existingResult = await _webServiceProvider.Of<IRedeliveryService>().GetExistingItemAsync(request.Barcode); if (existingResult.IsNullOr(x => x.IsNotValid)) { await InsertRecordAsync(); } else { UpdateDisplayAfterScan(existingResult.Value); } if (ExpandedInvoiceNumbers.Contains(scanResult.Value.InvoiceNo)) { var selectedSummary = RedeliveryDetails.FirstOrDefault(x => x.InvoiceNo == scanResult.Value.InvoiceNo); if (selectedSummary != null) { await GetScannedAndNotScannedItemsAsync(selectedSummary); } } OnUIUpdate?.Invoke(); // Invoke the UI update callback } catch (Exception ex) { var sr = new SuccessResultBuilder(); sr = sr.Invalid().WithError(ex); EmitResult(sr); return; } finally { SetAsIdle(); } } public void UpdateDisplayAfterScan(InvoiceSummary scanResult) { try { if (RedeliveryDetails.IsNullOrEmpty()) { RedeliveryDetails = new List<InvoiceSummary>(); } var matchingInvoice = RedeliveryDetails.FirstOrDefault(x => x.InvoiceNo == scanResult.InvoiceNo); if (matchingInvoice == null && _scanningMode == ScanningMode.Adding) { RedeliveryDetails.Add(scanResult); } else if (matchingInvoice != null) { matchingInvoice.Count = scanResult.Count; } ManualInput = false; _barcodeInput = string.Empty; SelectedReason = null; } catch (Exception ex) { var sr = new SuccessResultBuilder(); sr = sr.Invalid().WithError(ex); EmitResult(sr); return; } } // Other existing methods and properties }}Issue:
When I scan an item and choose a reason, the card must show up immediately. However, the card only appears after scanning the item again. I have tried invoking StateHasChanged() within the ViewModel, but this approach is not suitable for a Blazor ViewModel.
Attempts to Fix:
I added a callback delegate OnUIUpdate in the ViewModel and set it to StateHasChanged in the Razor component. The delegate is invoked after updating the data, but the card still does not show up on the initial scan.
I have ensured that UpdateDisplayAfterScan correctly updates the RedeliveryDetails list, but the UI does not refresh as expected on the first scan.
What is the best way to make the card appear immediately after the initial scan and reason selection?
Any help or suggestions would be appreciated!