How to scan driver's license (PDF417) using xamarin forms + zxing on iOS 10.2

问题

I am using Xamarin forms to write an iOS app and using the ZXing library to scan barcodes. I am trying to read a driver's license (PDF417) barcode, but the library is not able to recognize that barcode.

If I include UPC or other barcodes in the PossibleFormats, they are scanned correctly.

I am also certain the barcode I am trying to read is PDF417 barcode because Scandit is able to recognize it correctly while using only PDF417 barcode.

Here is the code I am using. What do I need to change so that the PDF417 barcode is recognized correctly?

async void Handle_Clicked (object sender, System.EventArgs e)
    {
        MobileBarcodeScanningOptions options = new MobileBarcodeScanningOptions ();
        options.PossibleFormats = new List<ZXing.BarcodeFormat> () {
            ZXing.BarcodeFormat.PDF_417
        };
        options.TryHarder = true;

        var scanPage = new ZXingScannerPage (options);


        scanPage.OnScanResult += (result) => {
            // Stop scanning
            scanPage.IsScanning = false;

            // Pop the page and show the result
            Device.BeginInvokeOnMainThread (async () => {
                await Navigation.PopAsync ();
                await DisplayAlert ("Scanned Barcode", result.Text, "OK");
            });
        };

        // Navigate to our scanner page
        await Navigation.PushAsync (scanPage);
    }

回答1:

I ran into this exact same issue a few days ago and fixed it with the following. In the MobileBarcodeScanningOptions class there's a property of type CameraResolutionSelectorDelegate called CameraResolutionSelector. You can set this to return a higher camera resolution from a list of available resolutions. So my instantiation of MobileBarcodeScanningOptions looks like this:

var options = new MobileBarcodeScanningOptions {
            TryHarder = true,
            CameraResolutionSelector = HandleCameraResolutionSelectorDelegate,
            PossibleFormats = new List<BarcodeFormat> { BarcodeFormat.PDF_417 }
        };

And my HandleCameraResolutionSelectorDelegate:

CameraResolution HandleCameraResolutionSelectorDelegate(List<CameraResolution> availableResolutions)
{
    //Don't know if this will ever be null or empty
    if (availableResolutions == null || availableResolutions.Count < 1)
        return new CameraResolution () { Width = 800, Height = 600 };

    //Debugging revealed that the last element in the list
    //expresses the highest resolution. This could probably be more thorough.
    return availableResolutions [availableResolutions.Count - 1];
}

That's all I needed to change to get a driver's license (PDF417) barcode to scan.

Here's the source code for MobileBarcodeScanningOptions.cs from ZXing github.

来源：https://stackoverflow.com/questions/42657211/how-to-scan-drivers-license-pdf417-using-xamarin-forms-zxing-on-ios-10-2

标签

Xamarin

xamarin.ios

barcode

zxing