xamarin xzing barcode scanner re-scan

问题

I'm using the zxing barcode scanner in xamarin android forms and I can get it to scan one barcode with no issues, but I want to be able to discard the scan they have taken and have the ability to take a another scan.

I'm also using MVVM. Here is my xaml...

 <Grid VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"></ColumnDefinition>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="*"></RowDefinition>
                <RowDefinition Height="Auto"></RowDefinition>
            </Grid.RowDefinitions>
          
            <forms:ZXingScannerView  x:Name="zxingView" 
                                     IsTorchOn="{Binding TorchON}"       
                                     IsScanning="{Binding IsScanning}" 
                                     IsAnalyzing="{Binding IsAnalyzing}"
                                     Result="{Binding Result, Mode=TwoWay}" 
                                     ScanResultCommand="{Binding ScanCommand}"
                                     />
            <forms:ZXingDefaultOverlay               
                x:Name="scannerOverlay"                                                       
                BottomText="Place the red line over the barcode you'd like to scan." />
            <Button Grid.Row="1" Text="Toggle Flash"  Command="{Binding FlashToggleCommand}"></Button>
        </Grid>

And this is my page model

private string barcode = string.Empty;

    public string Barcode
    {
        get { return barcode; }
        set { barcode = value; }
    }

    private bool _isAnalyzing = true;

    public bool IsAnalyzing
    {
        get { return _isAnalyzing; }
        set
        {
            if (!Equals(_isAnalyzing, value))
            {
                _isAnalyzing = value;
                OnPropertyChanged("IsAnalyzing");
            }
        }
    }

    private bool _isScanning = true;
    private bool _torchON = false;
    private DynamicContainerPageModel _hhtScreen;
    private readonly IDeviceManager _deviceManager;

    public ScanningViewPageModel(IDeviceManager deviceManager)
    {
        _deviceManager = deviceManager;
    }

    public override void Init(object initData)
    {
        base.Init(initData);
        _hhtScreen = initData as DynamicContainerPageModel;

    }


    public bool IsScanning
    {
        get { return _isScanning; }
        set
        {
            if (!Equals(_isScanning, value))
            {
                _isScanning = value;
                OnPropertyChanged("IsScanning");
            }
        }
    }

    public bool TorchON
    {
        set
        {
            if (_torchON != value)
            {
                _torchON = value;
                OnPropertyChanged("TorchON");
            }
        }
        get { return _torchON; }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public Command ScanCommand
    {
        get
        {
            return new Command(() =>

            {
                IsAnalyzing = false;
                IsScanning = false;

                Device.BeginInvokeOnMainThread(async () =>
                {
                    Barcode = Result.Text;
                    var response = await CoreMethods.DisplayAlert("Barcode found", "Found: " + Result.Text, "Keep",
                        "Scan Again");

                    if (response)
                    {
                        //Save the value into the model
                        _deviceManager.BeginInvokeOnMainThread(() =>
                                    {
                                        _hhtScreen.SelectedControl.Text = barcode;
                                    });

                        //close page
                        await this.CoreMethods.PopPageModel(false);
                    }
                    else
                    {
                        Result = null;
                        IsAnalyzing = true;
                        IsScanning = true;
                    }
                });

                IsAnalyzing = true;
                IsScanning = true;
            });
        }
    }

    public Command FlashToggleCommand
    {
        get { return new Command(async () => { TorchON = !TorchON; }); }
    }

    public Result Result { get; set; }

When I press scan again on my pop up, I find it a bit hit and miss whether the scanning camera activates again or not, majority of the time it just freezes. Am I doing something wrong? Is there a better way to get the control to rescan?

回答1:

I've hit a very similar problem in the past. What I had to end up doing was defining the Scanner view in the code behind, then conditionally add/remove from the view as needed. This is what mine ended up looking like:

The XAML:

    <!--
        The barcode scanner grid. The actual barcode scanner is
        created and added to the grid in the code behind class.
    -->
    <Grid x:Name="ScannerViewGrid"
          Grid.Row="3"
          HorizontalOptions="FillAndExpand"
          IsVisible="{Binding IsBarcodeScannerRunning}"
          VerticalOptions="FillAndExpand" />

The code behind:

private ZXingDefaultOverlay scannerOverlay;
private ZXingScannerView scannerView;

private void CreateNewScannerView()
{
    var vm = BindingContext.DataContext as SearchViewModel;

    ScannerViewGrid.Children.Clear();

    scannerOverlay = null;
    scannerView = null;

    scannerOverlay = new ZXingDefaultOverlay();
    scannerOverlay.ShowFlashButton = false;

    scannerView = new ZXingScannerView();
    scannerView.SetBinding(ZXingScannerView.ResultProperty, nameof(vm.BarcodeScanResult), BindingMode.OneWayToSource);
    scannerView.SetBinding(ZXingScannerView.ScanResultCommandProperty, nameof(vm.BarcodeScanResultCommand));
    scannerView.IsScanning = true;

    ScannerViewGrid.Children.Add(scannerView);
    ScannerViewGrid.Children.Add(scannerOverlay);
}

private void RemoveScannerView()
{
    ScannerViewGrid.Children.Clear();

    scannerView.IsScanning = false;
    scannerView.IsAnalyzing = false;
    scannerView.RemoveBinding(ZXingScannerView.ResultProperty);
    scannerView.RemoveBinding(ZXingScannerView.ScanResultCommandProperty);

    scannerView = null;
    scannerOverlay = null;
}

来源：https://stackoverflow.com/questions/63391275/xamarin-xzing-barcode-scanner-re-scan