A try to create a default widget totally in c++.

LectureWidget.cpp

// Fill out your copyright notice in the Description page of Project Settings.


#include "LectureWidget.h"
#include "Blueprint/WidgetTree.h"
#include "Components/Button.h"
#include "Components/Image.h"
#include "Components/CanvasPanel.h"
#include "Components/CanvasPanelSlot.h"
#include "Layout/Anchors.h"
#include "UObject/ConstructorHelpers.h"

ULectureWidget::ULectureWidget(const FObjectInitializer& ObjectInitializer): Super(ObjectInitializer){
	// Set icons textures
	static ConstructorHelpers::FObjectFinder<UTexture2D> HomeIconObj(TEXT("/Game/UI/Icons/home-outline"));
	static ConstructorHelpers::FObjectFinder<UTexture2D> MenuIconObj(TEXT("/Game/UI/Icons/th-list-outline"));
	static ConstructorHelpers::FObjectFinder<UTexture2D> ArrowLeftIconObj(TEXT("/Game/UI/Icons/arrow-left-outline"));
	static ConstructorHelpers::FObjectFinder<UTexture2D> ArrowRightIconObj(TEXT("/Game/UI/Icons/arrow-right-outline"));

	if (HomeIconObj.Object != NULL) HomeIconTexture = HomeIconObj.Object;
	if (MenuIconObj.Object != NULL) MenuIconTexture = MenuIconObj.Object;
	if (ArrowLeftIconObj.Object != NULL) ArrowLeftIconTexture = ArrowLeftIconObj.Object;
	if (ArrowRightIconObj.Object != NULL) ArrowRightIconTexture = ArrowRightIconObj.Object;
}

void ULectureWidget::NativeConstruct()
{
	Super::NativeConstruct();

	UCanvasPanel* Root = WidgetTree->ConstructWidget<UCanvasPanel>(UCanvasPanel::StaticClass(), FName("Canvas"));
	// UCanvasPanel* Root = Cast<UCanvasPanel>(GetRootWidget());

	
	WidgetTree->RootWidget = Root;
	UWidget* root = GetRootWidget();
	UE_LOG(LogTemp, Warning, TEXT("Root widget class: %s"), *root->GetClass()->GetName());

	// Create buttons and set them in a slot
	HomeButton = WidgetTree->ConstructWidget<UButton>(UButton::StaticClass(), FName("Home_Button"));
	HomeButton->WidgetStyle.Normal.SetResourceObject(Cast<UObject>(HomeIconTexture));
	HomeButton->WidgetStyle.Normal.SetImageSize(FVector2D(80.f, 80.f));
	HomeButton->WidgetStyle.Normal.DrawAs = ESlateBrushDrawType::Image;
	HomeButton->WidgetStyle.Normal.TintColor = FLinearColor(1.f, 0.f, .3f, 1.f);
	HomeButton->WidgetStyle.Normal.Margin = 0.f;
	// HomeButton->SetColorAndOpacity(FLinearColor(1.f, 1.f, 1.f, 0));

	UCanvasPanelSlot* HomeButtonSlot = Cast<UCanvasPanelSlot>(Root->AddChild(HomeButton));
	HomeButtonSlot->SetAnchors(FAnchors(.0f, .0f, .0f, .0f));
	HomeButtonSlot->SetSize(FVector2D(80.f, 80.f));
	HomeButtonSlot->SetPosition(FVector2D(80.f, 80.f));
	//HomeButtonSlot->SetAlignment(FVector2D(.5f, .5f));

	MenuButton = WidgetTree->ConstructWidget<UButton>(UButton::StaticClass(), FName("Menu_Button"));
	MenuButton->WidgetStyle.Normal.SetResourceObject(Cast<UObject>(MenuIconTexture));
	MenuButton->WidgetStyle.Normal.SetImageSize(FVector2D(80.f, 80.f));
	HomeButton->WidgetStyle.Normal.DrawAs= ESlateBrushDrawType::Image;
	MenuButton->WidgetStyle.Normal.Margin = 0.f;

	UCanvasPanelSlot* MenuButtonSlot = Cast<UCanvasPanelSlot>(Root->AddChild(MenuButton));
	MenuButtonSlot->SetAnchors(FAnchors(1.f, 0, 1.f, 0));
	MenuButtonSlot->SetSize(FVector2D(80.f, 80.f));
	MenuButtonSlot->SetPosition(FVector2D(-160.f, 80.f));

	ArrowLeftButton = WidgetTree->ConstructWidget<UButton>(UButton::StaticClass(), FName("ArrowLeft_Button"));
	ArrowLeftButton->WidgetStyle.Normal.SetResourceObject(Cast<UObject>(ArrowLeftIconTexture));
	ArrowLeftButton->WidgetStyle.Normal.SetImageSize(FVector2D(80.f, 80.f));
	ArrowLeftButton->WidgetStyle.Normal.DrawAs = ESlateBrushDrawType::Image;
	ArrowLeftButton->WidgetStyle.Normal.Margin = 0.f;

	UCanvasPanelSlot* ArrowLeftButtonSlot = Cast<UCanvasPanelSlot>(Root->AddChild(ArrowLeftButton));
	ArrowLeftButtonSlot->SetAnchors(FAnchors(0, 1.f, 0, 1.f));
	ArrowLeftButtonSlot->SetSize(FVector2D(80.f, 80.f));
	ArrowLeftButtonSlot->SetPosition(FVector2D(80.f, -200.f));

	ArrowRightButton = WidgetTree->ConstructWidget<UButton>(UButton::StaticClass(), FName("ArrowRight_Button"));
	ArrowRightButton->WidgetStyle.Normal.SetResourceObject(Cast<UObject>(ArrowRightIconTexture));
	ArrowRightButton->WidgetStyle.Normal.SetImageSize(FVector2D(80.f, 80.f));
	ArrowRightButton->WidgetStyle.Normal.DrawAs = ESlateBrushDrawType::Image;
	ArrowRightButton->WidgetStyle.Normal.Margin = 0.f;

	UCanvasPanelSlot* ArrowRightButtonSlot = Cast<UCanvasPanelSlot>(Root->AddChild(ArrowRightButton));
	ArrowRightButtonSlot->SetAnchors(FAnchors(1.f, 1.f, 1.f, 1.f));
	ArrowRightButtonSlot->SetSize(FVector2D(80.f, 80.f));
	ArrowRightButtonSlot->SetPosition(FVector2D(-160.f, -200.f));

	// Root->AddToRoot();

}

Nice page but it didn't work for me - had to move root creation from NativeConstruct to Initialize, as per comments on this post: https://forums.unrealengine.com/t/c-widget-does-not-show-anything-on-screen/453617/3

Nice page but it didn't work for me - had to move root creation from NativeConstruct to Initialize, as per comments on this post: https://forums.unrealengine.com/t/c-widget-does-not-show-anything-on-screen/453617/3

You can update this github with your solution.