I'm developing a Xamarin.Forms app. I have a button which triggers the Scanner.

<Button VerticalOptions="Center"
        IsVisible="False"
        Text="Scan"
        CornerRadius="10"
        FontSize="Medium"
        FontAttributes="Bold"
        TextColor="White"
        Clicked="Scan"
        x:Name="btnScan"/>

My scanning function is:

private async void Scan(object sender, EventArgs e)
    {
        PermissionStatus granted = await Permissions.CheckStatusAsync<Permissions.Camera>();
        if (granted != PermissionStatus.Granted)
        {
            _ = await Permissions.RequestAsync<Permissions.Camera>();
        }
        if (granted == PermissionStatus.Granted)
        {
            try
            {
                MobileBarcodeScanningOptions optionsCustom = new MobileBarcodeScanningOptions();

                scanner = new MobileBarcodeScanner();
                scanner.TopText = "Insert";
                scanner.BottomText = "Align red line with Barcode";

                optionsCustom.DelayBetweenContinuousScans = 3000;
                scanner.ScanContinuously(optionsCustom, ScanResult);

            }
            catch (Exception)
            {
                scanner.Cancel();
                Device.BeginInvokeOnMainThread(async () =>
                {
                    await DisplayAlert("Problem", "Something went wrong.", "ΟΚ");
                });
            }
        }
    }

The problem is after the scanner is actually opened, the OnSleep() method in App.xaml.cs is triggered.

protected override void OnSleep()
{
        
}

protected override void OnResume()
{
        
}

And after the scanner is closed the OnResume() method is triggered.

Is this behavior expected? Am i doing something wrong with the scanner initialization?

CodePudding user response：

Based on the comments, your question then becomes not to suppress the behaviour you're seeing but handle it. So you could put a static flag in the App class so you know the scanner is active and put your handler code inside this.

App.xaml.cs:

public static bool ScannerActive { get; set; }

protected override void OnSleep()
{
    if (!ScannerActive)
    {
        HandleOnSleep();
    }
}

protected override void OnResume()
{
    if (!ScannerActive)
    {
        HandleOnResume();
    }

    // Reset the flag if we are coming back from the scanner
    else App.ScannerActive = false;
}

Scanning function:

private async void Scan(object sender, EventArgs e)
{
    App.ScannerActive = true;

    try
    {
        // ... //
        scanner.ScanContinuously(optionsCustom, ScanResult);
    }
    catch (Exception)
    {
        // Reset flag if it crashed out
        App.ScannerActive = false;
    }
}