How to initialize bar code scanner on App startup.

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
                }
            };
        }