ZXing.Net.Mobile 没有立即开始扫描

Question

I have a page with ScannerView as MainPage. When I start the app it can't scan a barcode. I have to set another page as mainpage then navigate to the scanner page, before it can scan a barcode. Or lock and then unlock the phone, then it will start scanning.

App.xaml.cs:

MainPage = new NavigationPage(new ScannerPage());

ScannerPage.xaml:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyApp.Pages.ScannerPage"
             xmlns:zxing="clr-namespace:ZXing.Net.Mobile.Forms;assembly=ZXing.Net.Mobile.Forms">
    <ContentPage.Content>
        <Grid>
            <zxing:ZXingScannerView x:Name="ScannerView"
                                    IsScanning="True"
                                    IsAnalyzing="True" />
            <zxing:ZXingDefaultOverlay x:Name="ScannerOverlay"
                                       TopText="Hold your phone up to the QR code"
                                       BottomText="Scanning will happen automatically"
                                       ShowFlashButton="True"/>
        </Grid>
    </ContentPage.Content>
</ContentPage>

ScannerPage.xaml.cs:

public partial class ScannerPage : ContentPage
{
    public ScannerPage ()
    {
        InitializeComponent ();

        ScannerView.Options = new MobileBarcodeScanningOptions
        {
            PossibleFormats = new List<BarcodeFormat>
            {
                BarcodeFormat.DATA_MATRIX,
            },
            TryHarder = true
        };

        ScannerView.OnScanResult += (result) => Device.BeginInvokeOnMainThread(async () =>
        {
            ScannerView.IsAnalyzing = false;
            await DisplayAlert("Scanned", result.Text, "Ok");
            ScannerView.IsAnalyzing = true;
        });
    }
}

Answer 1

I ended up using the following code programmatically:

    public static async Task ScanConnection()
    {
            MobileBarcodeScanningOptions options = new ZXing.Mobile.MobileBarcodeScanningOptions()
                {
                    TryHarder = true,
                    PossibleFormats = new List<ZXing.BarcodeFormat>() { ZXing.BarcodeFormat.QR_CODE }
                };


                MobileBarcodeScanner scanner = new ZXing.Mobile.MobileBarcodeScanner();

                ZXing.Result result = await scanner.Scan(options);

                if (result != null && !string.IsNullOrEmpty(result.Text))
                {
                    ...
                }
    }

You could call that code from an overridden OnAppearing() method from within your derived page.

Answer 2

I had a similar issue. At the first invocation of the scanner page, it would attempt to scan but wouldn't recoqnise any barcodes. After exiting the page and re-opening it, the problem disappeared.

Solution that worked in my case was adding the following in two places:

ZXing.Mobile.MobileBarcodeScanner.Initialize(Application);

1. in AndroidManifest.xml

    ZXing.Net.Mobile.Forms.Android.Platform.Init();
    ZXing.Mobile.MobileBarcodeScanner.Initialize(Application);
    </manifest>

2. Also MainActivity.cs (yours may be different)

         public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
        {
            protected override void OnCreate(Bundle savedInstanceState)
            {
                TabLayoutResource = Resource.Layout.Tabbar;
                ToolbarResource = Resource.Layout.Toolbar;
                base.OnCreate(savedInstanceState);
                ZXing.Net.Mobile.Forms.Android.Platform.Init();
                ZXing.Mobile.MobileBarcodeScanner.Initialize(Application);
                global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
                LoadApplication(new App());
            }
            //needed for zxing scanner..
            public override void OnRequestPermissionsResult(int requestCode, string[] permissions, Permission[] grantResults)
            {
                global::ZXing.Net.Mobile.Android.PermissionsHandler.OnRequestPermissionsResult(requestCode, permissions, grantResults);
            }
        }