Testcase of issue with the Fusion 360 API that shows that setting an attribute on the design causes a selection input to loose it's selection

MinimalTestcase.cpp

#include <Core/CoreAll.h>
#include <Fusion/FusionAll.h>

#include <string>

using namespace adsk::core;
using namespace adsk::fusion;
using namespace std;

Ptr<Application> app;
Ptr<UserInterface> ui;

const char* BUTTON_NAME = "MinimalTestcaseButton";
const char* PANEL_TO_USE = "SolidScriptsAddinsPanel";
const char* COMMAND_ID = "MinimalTestcaseCmdId";
const char* FACES_INPUT = "facesSelection";
const char* ATTRIBUTE_GROUP = "MH-MinimalTestcase";
const char* ATTRIBUTE_TOLERANCE = "Tolerance";

// CommandExecuted event handler.
class OnExecuteEventHander : public adsk::core::CommandEventHandler
{
public:
	void notify(const Ptr<CommandEventArgs>& eventArgs) override
	{
		Ptr<Command> cmd = eventArgs->command();

		if (cmd) {

			Ptr<Design> design = app->activeProduct();
			if (!design) {
				ui->messageBox("No active Fusion design", "No Design");
				return;
			}

			Ptr<CommandInputs> inputs = cmd->commandInputs();

			Ptr<SelectionCommandInput> selectionInput = inputs->itemById(FACES_INPUT);

			size_t count1 = selectionInput->selectionCount();
			design->attributes()->add(ATTRIBUTE_GROUP, ATTRIBUTE_TOLERANCE, "value");
			size_t count2 = selectionInput->selectionCount();

			ui->messageBox(string("valid: ") + (selectionInput->isValid() ? "yes" : "no") 
				+ "  count1: " + to_string(count1) 
				+ "  count2: " + to_string(count2));
		}
	}
};

// CommandCreated event handler.
class CommandCreatedEventHandler : public adsk::core::CommandCreatedEventHandler
{
public:
	void notify(const Ptr<CommandCreatedEventArgs>& eventArgs) override
	{
		if (eventArgs)
		{

			// Get the command that was created.
			Ptr<Command> command = eventArgs->command();
			if (command)
			{

				// Connect to the execute event.
				Ptr<CommandEvent> onExecute = command->execute();
				if (!onExecute)
					return;
				bool isOk = onExecute->add(&onExecuteHandler);
				if (!isOk)
					return;

				// Get the CommandInputs collection associated with the command.
				Ptr<CommandInputs> inputs = command->commandInputs();
				if (!inputs)
					return;

				Ptr<SelectionCommandInput> facesSelectionInput = inputs->addSelectionInput(FACES_INPUT, "Faces to export", "Faces to export");
				if (!facesSelectionInput)
					return;
			}
		}
	}
private:
	OnExecuteEventHander onExecuteHandler;
} _cmdCreatedHandler;




extern "C" XI_EXPORT bool run(const char* context)
{
	app = Application::get();
	if (!app)
		return false;

	ui = app->userInterface();
	if (!ui)
		return false;

	// Create a button command definition.
	Ptr<CommandDefinitions> cmdDefs = ui->commandDefinitions();
	Ptr<CommandDefinition> cmdDef = cmdDefs->addButtonDefinition(COMMAND_ID,
		"Export faces to DXF",
		"");

	Ptr<ToolbarPanel> addinsPanel = ui->allToolbarPanels()->itemById(PANEL_TO_USE);
	Ptr<ToolbarControl> cntrl = addinsPanel->controls()->itemById(COMMAND_ID);
	if (!cntrl) {
		addinsPanel->controls()->addCommand(cmdDef);
	}


	// Connect to the Command Created event.
	Ptr<CommandCreatedEvent> commandCreatedEvent = cmdDef->commandCreated();
	commandCreatedEvent->add(&_cmdCreatedHandler);


	return true;
}




extern "C" XI_EXPORT bool stop(const char* context)
{
	if (ui)
	{
		// Create the command definition.
		Ptr<CommandDefinitions> commandDefinitions = ui->commandDefinitions();

		if (!commandDefinitions) {
			ui = nullptr;
			return false;
		}


		// Clean up the UI.

		Ptr<CommandDefinition> cmdDef = commandDefinitions->itemById(COMMAND_ID);
		if (cmdDef) {
			cmdDef->deleteMe();
		}
		else
			ui->messageBox("unable to find cmdDef to delete it!");

		Ptr<ToolbarPanel> addinsPanel = ui->allToolbarPanels()->itemById(PANEL_TO_USE);
		Ptr<ToolbarControl> cntrl = addinsPanel->controls()->itemById(COMMAND_ID);
		if (cntrl) {
			cntrl->deleteMe();
		}
		else
			ui->messageBox("unable to find cntrl to delete it!");

		ui = nullptr;
		return true;
	}

	return true;
}



#ifdef XI_WIN

#include <windows.h>

BOOL APIENTRY DllMain(HMODULE hmodule, DWORD reason, LPVOID reserved)
{
	switch (reason)
	{
	case DLL_PROCESS_ATTACH:
	case DLL_THREAD_ATTACH:
	case DLL_THREAD_DETACH:
	case DLL_PROCESS_DETACH:
		break;
	}
	return TRUE;
}

#endif // XI_WIN