Reason for "Unresolved symbol winrt::Windows::UI::Xaml::Input::TappedEventHandler" ?

[andrew7webb]

void myButtonTapped(
    winrt::Windows::IInspectable const & sender,
    const Windows::UI::Xaml::RoutedEventArgs & args)
{
    textBlock.Text( L"Tapped" );
}

void OnLaunched(LaunchActivatedEventArgs const &)
{
    buttonM.Tapped({ this, &HelloGui::myButtonTapped });
    // error LNK2019 : unresolved external symbol winrt::Windows::UI::Xaml::Input::TappedEventHandler::TappedEventHandler
    //  <class HelloGui,void (__cdecl HelloGui::*)(struct winrt::Windows::IInspectable const &,struct winrt::Windows::UI::Xaml::RoutedEventArgs const &)>
    // 
    // referenced in function HandleTapped(void)

I thought to try a button Tapped event handler instead of a Click. It compiled, but did not link.

[ajorians]

Hi @andrew7webb ,

You need to add the include for TappedEventHandler which is what the Tapped method is taking. So add:

#include "winrt/Windows.UI.Xaml.Input.h"

Once you do that you'll have a compile error instead of a linking error. But then change:

buttonM.Tapped({ this, &HelloGui::myButtonTapped });

to:

buttonM.Tapped({ &HelloGui::myButtonTapped });

And that worked for me! 😃

[andrew7webb]

The additional include helped the problem, but because button was a class member in my code, I still needed to use
buttonM.Tapped({ this, &HelloGui::myButtonTapped });

My declaration of buttonM....
class HelloGui : public ApplicationT
{
public:
Button buttonM, buttonL, buttonM2;

And now it works. 😃 Thank you.

[kennykerr]

That’s right. Generally, when you hit a linker error it means that you’re using definitions from a namespace you haven’t included. Some other namespace pulled in the declarations but the definitions aren't included automatically to reduce build time. Hopefully C++ modules will make this problem go away in future.