问题
I'm using ZXing barcode scanner plugin for my Xamarin.Forms project. According to some posts, I need to use custom overlay for ZXing scanner in order to have cancel button. But I'm not familiar with Android development in a Xamarin.Forms project.
So far, I know a scanner (MobileBarcodeScanner of ZXing plugin) accept an Android.Views.View as an overlay to replace the default scanning page view.
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;
}
But I don't know how to create a view page (either in XML design or programmatically) and set it to scanner.CustomOverlay.
I'm not sure if a common Android view can be used for scanner, any detailed reference would be really appreicated.
Thanks.
回答1:
If you want to customize the overlay, you must create your own View for each platform. You can customize your overlay like this( create a custom overlay called ZxingOverlayView set it to the scanner.CustomOverlay):
var scanner = new ZXing.MobileMobileBarcodeScanner();
scanner.UseCustomOverlay = true;
myCustomOverlayInstance = new ZxingOverlayView(this, scanner);
scanner.CustomOverlay = myCustomOverlayInstance;
ZxingOverlayView should inherit the view then add your control to the custom view.
You can see details about this link.
http://slackshotindustries.blogspot.com/2013/04/creating-custom-overlays-in-xzing.html
Edit
There are completely steps.
First of all, you could create a interface for dependence service.
public interface IDeviceService
{
Task<string> ScanAsync();
}
You can use this interface in the PCL code.
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");
}
}
In the android platform. You can design your layout. First of all, create a layout
<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>
Then achieve the dependence service interface and use your new layout.
[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 code.
[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;
}
}
Here is running GIF.
Here is a good simple code. you could refer to it. https://github.com/Wenfengcheng/ZXing.Sample_Xamarin
来源：https://stackoverflow.com/questions/57303386/how-to-create-and-implement-a-android-customoverlay-for-zxing-scanner