How to initialize bar code scanner on App startup - xamarin.forms

Question

I have a requirement for my xamarin cross platform application that as soon as app start up .QR Scanner set in to read the code. on completing scanning a beep will be ring up.and app again ready for next scanning how can i get this done. what i have done is on button click scanner start, its read code, then i have to press button again to start it again.
public HomePage()
{
Button scanBtn = new Button
{
Text = "Scan Barcode",
HorizontalOptions = LayoutOptions.FillAndExpand,
};
scanBtn.Clicked += async (sender, args) =>
{
var scanResult = await Acr.BarCodes.BarCodes.Instance.Read();
if (!scanResult.Success)
{
await this.DisplayAlert("Alert ! ", "Sorry ! \n Failed to read the Barcode !", "OK");
}
else
{
var endpoint = new EndpointAddress("http://192.168.15.33/SMS/WebServices/SMSService.svc");
var binding = new BasicHttpBinding
{
Name = "basicHttpBinding",
MaxBufferSize = 2147483647,
MaxReceivedMessageSize = 2147483647
};
TimeSpan timeout = new TimeSpan(0, 0, 30);
binding.SendTimeout = timeout;
binding.OpenTimeout = timeout;
binding.ReceiveTimeout = timeout;
_client = new SMSServiceClient(binding, endpoint);
_client.ValidateStudentAsync("123-admin");
_client.ValidateStudentCompleted += _client_ValidateStudentCompleted; ;
// await this.DisplayAlert("Scan Successful !", String.Format("Barcode Format : {0} \n Barcode Value : {1}", scanResult.Format, scanResult.Code), "OK");
}
};
Content = new StackLayout
{
Children = {
scanBtn
}
};
}
and in app.cs
public class App : Application
{
public App()
{
// The root page of your application
MainPage = new HomePage();
}
protected override void OnStart()
{
MainPage = new HomePage();
}
protected override void OnSleep()
{
MainPage = new HomePage();
}
protected override void OnResume()
{
MainPage = new HomePage();
}
}

Answer 1

You can use ZXing.Net.Mobile for Forms to read QR codes. To initialize this plugin you should call method to init into each project (Android, iOS, UWP) like this:
For Android in MainActivity.cs class call:
ZXing.Net.Mobile.Forms.Droid.Platform.Init();
For iOS in AppDeletage.cs class call
ZXing.Net.Mobile.Forms.iOS.Platform.Init();
And finally to read QR Codes:
private async void Scan() {
var scanPage = new ZXingScannerPage();
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);
}