Undefined symbols for architecture x86_64: FArguments const& in XCode

Hi, I have created a project using the blank C++ template and am trying to create a custom widget and put it into a HUD.

When compiling from XCode or Unreal editor, I get the error:

Undefined symbols for architecture x86_64:
  "SSettingsWindow::Construct(SSettingsWindow::FArguments const&)", referenced from:
      AMasterRobotHUD::buildControlPanels() in MasterRobotHUD.cpp.o

I am using Unreal 4.14 and XCode 8 on MacOS Sierra.
This is how I am adding the widget to a subclass of AHUD:

GEngine->GameViewport->AddViewportWidgetContent(
                                                                SNew(SWeakWidget)
                                                                .PossiblyNullContent(settingsWindow.ToSharedRef())
                                                                );

This is how the class for settingsWindow looks like. .h file:

#pragma once

#include "Widgets/SCompoundWidget.h"

class AMasterRobotHUD;

/**
 * 
 */
class THEHIVEMIND_API SSettingsWindow : public SCompoundWidget
{
public:
    SLATE_BEGIN_ARGS(SSettingsWindow)
    : _ownerHUD()
    {}
    
    SLATE_ARGUMENT(TWeakObjectPtr<AMasterRobotHUD>, ownerHUD)
    
    SLATE_END_ARGS()


	/** Constructs this widget with InArgs */
	void Construct(const FArguments& InArgs);

};

And cpp file:

#include "TheHiveMind.h"
#include "SSettingsWindow.h"
#include "SlateOptMacros.h"

void SSettingsWindow::Construct(const FArguments& InArgs)
{
	
	/*ChildSlot
	[
		// Populate the widget
	];*/
}

This is in my build.cs file:

PublicDependencyModuleNames.AddRange(
            new string[] {
                "Core",
                "CoreUObject",
                "Engine",
                "InputCore"
            }
        );

        PrivateDependencyModuleNames.AddRange(
            new string[] {
                "Slate",
                "SlateCore"

            }
        );

I have tried editing the build.cs file, then clicking “Refresh XCode project” in the Unreal editor, with no luck. Am I missing something else that needs to be done?