如何为 ZXing Scanner 创建和实现 Android CustomOverlay？

Question

我正在为我的 Xamarin.Forms 项目使用 ZXing 条码扫描器插件。根据一些帖子，我需要为 ZXing 扫描仪使用自定义覆盖才能获得取消按钮。但我不熟悉 Xamarin.Forms 项目中的 Android 开发。

到目前为止，我知道一个扫描仪（ZXing 插件的 MobileBarcodeScanner）接受一个 Android.Views.View 作为覆盖来替换默认的扫描页面视图。

public async Task<string> ScanAsync()
{
    MobileBarcodeScanner scanner = new MobileBarcodeScanner();
    scanner.UseCustomOverlay = true;
    scanner.CustomOverlay = ???????;

    var scanResult = await scanner.Scan();
    if (scanResult != null)
    { return scanResult.Text; }
    return null;
}

但我不知道如何创建视图页面（在 XML 设计中或以编程方式）并将其设置为scanner.CustomOverlay。

我不确定是否可以将通用的 Android 视图用于扫描仪，任何详细的参考资料都会非常感激。

谢谢。

Answer 1

如果要自定义叠加层，则必须为每个平台创建自己的视图。您可以像这样自定义叠加层（创建一个名为 ZxingOverlayView 的自定义叠加层，将其设置为 scanner.CustomOverlay）：

var scanner = new ZXing.MobileMobileBarcodeScanner();
scanner.UseCustomOverlay = true;
myCustomOverlayInstance = new ZxingOverlayView(this, scanner);
scanner.CustomOverlay = myCustomOverlayInstance;

ZxingOverlayView 应该继承 view 然后将您的控件添加到自定义视图。 您可以查看有关此链接的详细信息。

http://slackshotindustries.blogspot.com/2013/04/creating-custom-overlays-in-xzing.html

编辑

有完整的步骤。

首先，你可以为依赖服务创建一个接口。

 public interface IDeviceService
  {
    Task<string> ScanAsync();
  }

您可以在 PCL 代码中使用此接口。

  private async void DependencyButton_Clicked(object sender, EventArgs e)
    {
        var result = await DependencyService.Get<IDeviceService>().ScanAsync();
        if (!string.IsNullOrEmpty(result))
        {
            await DisplayAlert(result, null, "OK");
        }
    }

在安卓平台。你可以设计你的布局。首先，创建一个布局

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
    android:id="@+id/imgClose"
    android:layout_width="30dp"
    android:layout_height="30dp"
    android:src="@drawable/close"
    android:layout_marginTop="20dp"
    android:layout_marginLeft="20dp"/>
  <RelativeLayout
    android:id="@+id/llScan"
    android:layout_width="240dp"
    android:layout_height="240dp"
    android:layout_centerInParent="true"
    android:background="@drawable/scan">
  <ImageView
        android:id="@+id/imgLine"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:adjustViewBounds="true"
        android:src="@drawable/scan_line"
        android:layout_centerHorizontal="true" />
     </RelativeLayout>
  <View
    android:id="@+id/viewTop"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_above="@id/llScan"
    android:background="@color/title_black"/>
 <View
    android:id="@+id/viewBottom"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@id/llScan"
    android:background="@color/title_black"
    android:layout_alignParentBottom="true"/>
 <View
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@id/viewTop"
    android:layout_toLeftOf="@id/llScan"
    android:layout_above="@id/viewBottom"
    android:background="@color/title_black"/>
 <View
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@id/viewTop"
    android:layout_above="@id/viewBottom"
    android:layout_toRightOf="@id/llScan"
    android:background="@color/title_black"/>
 </RelativeLayout>

然后实现依赖服务接口，使用你的新布局。

 [assembly: Xamarin.Forms.Dependency(typeof(DeviceService))]
 namespace Sample.Droid
 {
  public class DeviceService : IDeviceService
 {
    public async Task<string> ScanAsync()
    {
        var scanner = new ZXing.Mobile.MobileBarcodeScanner
        {
            UseCustomOverlay = true

        };
        //scanner.CustomOverlay = new CustomScanView(Application.Context);
        var options = new ZXing.Mobile.MobileBarcodeScanningOptions()
        {
            TryHarder = true,
            AutoRotate = false,
            UseFrontCameraIfAvailable = false,
            CameraResolutionSelector = new CameraResolutionSelectorDelegate(SelectLowestResolutionMatchingDisplayAspectRatio),
            PossibleFormats = new List<ZXing.BarcodeFormat>()
            {
                ZXing.BarcodeFormat.QR_CODE
            }
        };

        View scanView = LayoutInflater.From(Application.Context).Inflate(Resource.Layout.ScanView, null);
        ImageView imgLine = scanView.FindViewById<ImageView>(Resource.Id.imgLine);
        ImageView imgClose = scanView.FindViewById<ImageView>(Resource.Id.imgClose);
        imgClose.Click += delegate
        {
            scanner.Cancel();
        };
        scanner.CustomOverlay = scanView;

        ObjectAnimator objectAnimator = ObjectAnimator.OfFloat(imgLine, "Y", 0, DpToPixels(240));
        objectAnimator.SetDuration(2500);
        objectAnimator.RepeatCount = -1;
        objectAnimator.SetInterpolator(new LinearInterpolator());
        objectAnimator.RepeatMode = ValueAnimatorRepeatMode.Restart;
        objectAnimator.Start();

        ZXing.Result scanResults = await scanner.Scan(CrossCurrentActivity.Current.Activity, options);
        if (scanResults != null)
        {
            return scanResults.Text;
        }
        return string.Empty;
    }

    private int DpToPixels(double dp)
    {
        return (int)(dp * Application.Context.Resources.DisplayMetrics.Density);
    }

    private CameraResolution SelectLowestResolutionMatchingDisplayAspectRatio(List<CameraResolution> availableResolutions)
    {
        CameraResolution result = null;
        //a tolerance of 0.1 should not be visible to the user
        double aspectTolerance = 0.1;
        var displayOrientationHeight = DeviceDisplay.MainDisplayInfo.Orientation == DisplayOrientation.Portrait ? DeviceDisplay.MainDisplayInfo.Height : DeviceDisplay.MainDisplayInfo.Width;
        var displayOrientationWidth = DeviceDisplay.MainDisplayInfo.Orientation == DisplayOrientation.Portrait ? DeviceDisplay.MainDisplayInfo.Width : DeviceDisplay.MainDisplayInfo.Height;
        //calculatiing our targetRatio
        var targetRatio = displayOrientationHeight / displayOrientationWidth;
        var targetHeight = displayOrientationHeight;
        var minDiff = double.MaxValue;
        //camera API lists all available resolutions from highest to lowest, perfect for us
        //making use of this sorting, following code runs some comparisons to select the lowest resolution that matches the screen aspect ratio and lies within tolerance
        //selecting the lowest makes Qr detection actual faster most of the time
        foreach (var r in availableResolutions.Where(r => Math.Abs(((double)r.Width / r.Height) - targetRatio) < aspectTolerance))
        {
            //slowly going down the list to the lowest matching solution with the correct aspect ratio
            if (Math.Abs(r.Height - targetHeight) < minDiff)
                minDiff = Math.Abs(r.Height - targetHeight);
            result = r;
        }
        return result;
    }
   }

}

IOS 代码。

[assembly: Xamarin.Forms.Dependency(typeof(DeviceService))]
namespace Sample.iOS
{
public class DeviceService : IDeviceService
{
    public async Task<string> ScanAsync()
    {
        var scanner = new ZXing.Mobile.MobileBarcodeScanner()
        {
            UseCustomOverlay = true
        };

        var options = new ZXing.Mobile.MobileBarcodeScanningOptions()
        {
            TryHarder = true,
            AutoRotate = false,
            UseFrontCameraIfAvailable = false,
            PossibleFormats = new List<ZXing.BarcodeFormat>()
            {
                ZXing.BarcodeFormat.QR_CODE
            }
        };

        ScannerOverlayView customOverlay = new ScannerOverlayView();
        customOverlay.OnCancel += () =>
        {
            scanner?.Cancel();
        };
        customOverlay.OnResume += () =>
        {
            scanner?.ResumeAnalysis();
        };
        customOverlay.OnPause += () =>
        {
            scanner?.PauseAnalysis();
        };
        scanner.CustomOverlay = customOverlay;


        ZXing.Result scanResults = null;
        scanResults = await scanner.Scan(options);
        //customOverlay.Dispose();
        if (scanResults != null)
        {
            return scanResults.Text;
        }
        return string.Empty;
    }
}

这里正在运行 GIF。

这是一个很好的简单代码。你可以参考一下。 https://github.com/Wenfengcheng/ZXing.Sample_Xamarin