Cannot find unhandled exception error due to code not showing

Question

I have an error I can't find. it produces this message: System.NullReferenceException: Object reference not set to an instance of an object. There is no code shown as it is excecuting externally. This project is based on ble and uses this plugin: https://github.com/xabre/xamarin-bluetooth-le

private BluetoothAdapter adapter;
    protected override async void OnCreate(Bundle bundle)
    {
        TabLayoutResource = Resource.Layout.Tabbar;
        ToolbarResource = Resource.Layout.Toolbar;
        base.OnCreate(bundle);
        global::Xamarin.Forms.Forms.Init(this, bundle);
        LoadApplication(new App());
        adapter = BluetoothAdapter.DefaultAdapter;
        MainActivity main = new MainActivity();
        adapter.Enable();
        //main.enableBluetoothOnDevice();
        await scanAsync();
    }
    List<Plugin.BLE.Abstractions.Contracts.IDevice> deviceList = new List<Plugin.BLE.Abstractions.Contracts.IDevice>();
    public async System.Threading.Tasks.Task scanAsync()
    {            
        MainPage page1 = new MainPage();            
        var ble = CrossBluetoothLE.Current;
        var adapter = CrossBluetoothLE.Current.Adapter;
        var state = ble.State;
        ble.StateChanged += (s, e) =>
        {
        };
        adapter.DeviceDiscovered += (s, a) => deviceList.Add(a.Device);
        await adapter.StartScanningForDevicesAsync();            
        int index = deviceList.FindIndex(item => item.Name == "CTQBLE");
        if (index >= 0)
        {         
            try
                {
                await adapter.ConnectToDeviceAsync(deviceList.Where(i => i.Name == "CTQBLE").FirstOrDefault());
                bleRecieveAsync();  //Error occurs here
                page1.deviceConnected();

                }
            catch (DeviceConnectionException e)
                {
                    page1.deviceNotConnected();
                }
        }    
        else
        {
            page1.deviceNotConnected();
            return;
        }
    }

    public async void  bleRecieveAsync()
    {
        var service1 = await deviceList.Where(i => i.Name == "CTQBLE").FirstOrDefault().GetServiceAsync(Guid.Parse("abcd0021-9c79-4ed6-a382-50946d830c3f"));
        var characteristicFirmware = await service1.GetCharacteristicAsync(Guid.Parse("abcd0022-9c79-4ed6-a382-50946d830c3f"));
        var bytesFirmware = await characteristicFirmware.ReadAsync();

        var service2 = await deviceList.Where(i => i.Name == "CTQBLE").FirstOrDefault().GetServiceAsync(Guid.Parse("abcd0021-9c79-4ed6-a382-50946d830c3f"));
        var characteristicRunState = await service2.GetCharacteristicAsync(Guid.Parse("abcd0023-9c79-4ed6-a382-50946d830c3f"));
        var bytesRunState = await characteristicRunState.ReadAsync();

        var service3 = await deviceList.Where(i => i.Name == "CTQBLE").FirstOrDefault().GetServiceAsync(Guid.Parse("abcd0021-9c79-4ed6-a382-50946d830c3f"));
        var characteristicConfig = await service3.GetCharacteristicAsync(Guid.Parse("abcd0024-9c79-4ed6-a382-50946d830c3f"));
        var bytesConfig = await characteristicConfig.ReadAsync();

        var service4 = await deviceList.Where(i => i.Name == "CTQBLE").FirstOrDefault().GetServiceAsync(Guid.Parse("abcd0021-9c79-4ed6-a382-50946d830c3f"));
        var characteristicError = await service4.GetCharacteristicAsync(Guid.Parse("abcd0025-9c79-4ed6-a382-50946d830c3f"));
        var bytesError = await characteristicError.ReadAsync();

        var service5 = await deviceList.Where(i => i.Name == "CTQBLE").FirstOrDefault().GetServiceAsync(Guid.Parse("abcd0021-9c79-4ed6-a382-50946d830c3f"));
        var characteristicCommand = await service5.GetCharacteristicAsync(Guid.Parse("abcd0026-9c79-4ed6-a382-50946d830c3f"));
        var bytesCommand = await characteristicCommand.ReadAsync();
    }

Use the debugger to step through your code to determine which line causes it. Or add some try catch blocks to narrow it down. — Jason, Sep 10 '18 at 16:49
There is a comment in place where the error occurs @Jason Its beside the method call for bleRecieveAsync — Bleari, Sep 10 '18 at 16:54
You need to use `await bleRecieveAsync();`. Also, `bleRecieveAsync` should be an `async Task` not `async void` — Camilo Terevinto, Sep 10 '18 at 16:55
@CamiloTerevinto I altered the code to your suggestion, the error still occurs — Bleari, Sep 10 '18 at 16:59
Of course it exists, but now you can properly debug the asynchronous flow. — Camilo Terevinto, Sep 10 '18 at 17:00
When the changes are implemented and I step through the code it jumps from the method to the return line in the else block, and then jumps back to the end of the method. Is this what could cause the error? @CamiloTerevinto — Bleari, Sep 10 '18 at 17:08
The actual issue was that characteristicCommand was not being broadcast by the ble device. Thanks for the help. — Bleari, Sep 10 '18 at 17:20

Cannot find unhandled exception error due to code not showing

0 Answers0