将 IsScanning 属性从 False 更改为 True 后 C# Xamarin ZXing 无法扫描条形码

Posted 2023-03-25

【中文标题】将 IsScanning 属性从 False 更改为 True 后 C# Xamarin ZXing 无法扫描条形码

【英文标题】：C# Xamarin ZXing Unable to Scan Barcode after Change IsScanning Property from False to True

【发布时间】：2021-10-03 07:29:58

【问题描述】：

我有一个条形码扫描仪页面，即 BarcodeScannerView 和 BarcodeScannerViewModel。这样做的主要目的是在读取条形码后导航到另一个页面。我所做的是扫描条形码后应用程序成功导航到其他页面。在导航到下一页之前，我设置了 IsScanning = false 以防止下一次扫描。但是，当我尝试返回条形码扫描仪页面时，我设置了属性 IsScanning = true 但扫描仪不再工作。关于如何解决这个问题的任何想法？

条形码扫描仪视图

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         x:Class="MultiPosApp.InventorySystem.Views.BarcodeScannerView"
         NavigationPage.HasNavigationBar="False"
         xmlns:prism="http://prismlibrary.com"
         prism:ViewModelLocator.AutowireViewModel="True"
         xmlns:zxing="clr-namespace:ZXing.Net.Mobile.Forms;assembly=ZXing.Net.Mobile.Forms"
         xmlns:zxcm="clr-namespace:ZXing.Common;assembly=zxing.portable">


<Grid RowSpacing="0" ColumnSpacing="0" BackgroundColor="Transparent" Margin="0" VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand">
    <zxing:ZXingScannerView x:Name="scanner" Grid.RowSpan="3" Grid.ColumnSpan="3" 
                            ScanResultCommand="Binding ScanResultCommand" 
                            Result="Binding BarcodeResult, Mode=TwoWay"
                            IsScanning="Binding IsScanning, Mode=TwoWay"
                            IsAnalyzing="Binding IsAnalyzing, Mode=TwoWay"
                            VerticalOptions="CenterAndExpand"
                            HorizontalOptions="CenterAndExpand"/>

    <zxing:ZXingDefaultOverlay  Grid.RowSpan="3" 
                                Grid.ColumnSpan="3"                                                                
                                BottomText="Place the red line over the barcode you'd like to scan."  />
    
</Grid>
</ContentPage>

BarcodeScannerViewModel

public class BarcodeScannerViewModel : ViewModelBase

    #region Variables
    private INavigationService m_NavigationService;
    private IEventAggregator m_EventAggregator;
    private SQLDbConnection Conn;

    public DelegateCommand ScanResultCommand  get; set; 

    private ZXing.Result m_BarcodeResult;
    public ZXing.Result BarcodeResult
    
        get  return m_BarcodeResult; 
        set  SetProperty(ref m_BarcodeResult, value); 
    

    private bool m_IsScanning = true;
    public bool IsScanning
    
        get  return m_IsScanning; 
        set  SetProperty(ref m_IsScanning, value); 
    

    private bool m_IsAnalyzing = true;
    public bool IsAnalyzing
    
        get  return m_IsAnalyzing; 
        set  SetProperty(ref m_IsAnalyzing, value); 
    

    private string m_Barcode;
    public string Barcode
    
        get  return m_Barcode; 
        set  SetProperty(ref m_Barcode, value); 
    
    #endregion

    #region Constructor
    public BarcodeScannerViewModel(INavigationService navigationService, IEventAggregator eventAggregator, SQLDbConnection sql) : base(navigationService)
    
        m_NavigationService = navigationService;
        m_EventAggregator = eventAggregator;
        Conn = sql;

        ScanResultCommand = new DelegateCommand(OnScanResult);
    
    #endregion


    #region Method
    private void OnScanResult()
    
        IsAnalyzing = false;
        IsScanning = false;

        Device.BeginInvokeOnMainThread(async () =>
        
            
                string barcode = BarcodeResult.Text;
                await m_NavigationService.NavigateAsync("RegisterGoodsView");

                IsAnalyzing = true;
                IsScanning = true;  
        );
    

    public override void OnNavigatedTo(INavigationParameters parameters)
    
        Device.BeginInvokeOnMainThread(async () =>
        
            IsAnalyzing = true;
            IsScanning = true;
        );
    
    #endregion

【问题讨论】：

Mods 不会让我发布作为答案，我不能将您的问题标记为重复，因为 question 这个答案来自没有被赞成或接受的答案，所以给你：***.com/a/63397456/8395242

【参考方案1】：

但是，当我尝试返回条形码扫描仪页面时，我设置了属性 IsScanning = true 但扫描仪不再工作。

首先，您需要确认您在导航到页面之前或之后使用相同的 BarcodeScannerViewModel 实例。

那么你需要实现INotifyPropertyChanged接口来通知IsScanning值改变了。

public class ViewModelBase : INotifyPropertyChanged

    
    public event PropertyChangedEventHandler PropertyChanged;
  
    public void RaisePropertyChanged(string propertyName)
    
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        
            handler(this, new PropertyChangedEventArgs(propertyName));
        
    


private bool m_IsScanning = true;
    public bool IsScanning
    
        get  return m_IsScanning; 
        set
        
            m_IsScanning = value;
            RaisePropertyChanged("IsScanning");