Exception thrown in BluetoothLE sample using c++

[hayesgreg]

I'm writing a program to automatically test a BluetoothLE device I have developed. To get started I downloaded the BluetoothLE sample app from https://github.com/microsoft/Windows-universal-samples/tree/master/Samples/BluetoothLE and got the cs program working ok, however I cannot get the c++ program to work.

The app builds ok and I can run it on a remote PC with Remote Machine Debuging. The app starts ok and in scenario1_Discovery enumerates a BluetoothLE Heart Rate Moniter (HRM).
I select the HRM and go to scenario2_Client, click connect and the HRM connects.
The Service comboBox shows and I can click on HeartRateService ok.
The Characteristic comboBox shows but when I click on HeartRateMeasurement characteristic the program crashes with Exception error and the following message:

• Exception thrown at 0x76734402 (KernelBase.dll) in BluetoothLE.exe: WinRT originate error - 0x80004002 : 'No such interface supported'.
• Exception thrown at 0x76734402 in BluetoothLE.exe: Microsoft C++ exception: winrt::hresult_no_interface at memory location 0x03A9CEA0.
• Debug Error!
• Program: ...SDKSamples.BluetoothLE.CPPVS.Debug_Win32.Greg\BluetoothLE.exe

It appears to fail on line 313 of Scenario2_Client.cpp
selectedCharacteristic = selectedItem ? selectedItem.Tag().as() : nullptr;

Scenario2_Client.cpp:

fire_and_forget Scenario2_Client::CharacteristicList_SelectionChanged()
    {
        auto lifetime = get_strong();
	auto selectedItem = ServiceList().SelectedItem().as<ComboBoxItem>();
        
313     selectedCharacteristic = selectedItem ? selectedItem.Tag().as<GattCharacteristic>() : nullptr;
        
        if (selectedCharacteristic == nullptr)
        {
            EnableCharacteristicPanels(GattCharacteristicProperties::None);
            rootPage.NotifyUser(L"No characteristic selected", NotifyType::ErrorMessage);
            co_return;
        }
	.
        .
        .
  }

Can I get help solving this problem please. I'm new to c++ so finding it difficult.

Win 10.0.18363.836
VS Community 2019 Version 16.6.1
Thanks, Greg

[alexredko]

The bug is at the line
auto selectedItem = ServiceList().SelectedItem().as<ComboBoxItem>();
There shoud be CharacteristicList instead of ServiceList :
auto selectedItem = CharacteristicList().SelectedItem().as<ComboBoxItem>();

[galaxy-tek]

great, thanks for your answer.
i have got stuck in this issue for several days.
how can Microsoft publish such a bug demo!

[oldnewthing]

Sorry. The Bluetooth team wrote the C# sample, and I translated it to C++/WinRT. I'm good with C++/WinRT but I don't work on Bluetooth, so I just translate it as best I can and sometimes I mess up.

Fix is available in ad9a0c4 v13.0.4