new Widget not following parent window size

Ragbot

Hey guys im tyringto make it so that
when I double click on list it show shows me the items details but when I do that the new widget that I call does not follow the constraints I tried setting it as central widget but it does not go back to the old page if do that what should I do this is my code

mainwindow.cpp

#include "mainwindow.h"
#include "./ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    manga = new MangaDex();
    viewer = new MangaViewer(this);
    viewer->hide();
}

MainWindow::~MainWindow()
{
    delete manga;
    delete ui;
}

void MainWindow::on_SearchButton_clicked()
{
    manga_list = manga->search(ui->SearchEntry->text().toStdString());

    ui->Pages->clear();

    for (Manga i: manga_list)
    {
        ui->Pages->addItem(i.title.c_str());
    }
}


void MainWindow::on_SearchEntry_returnPressed()
{
    this->on_SearchButton_clicked();
}

void MainWindow::on_Pages_itemDoubleClicked(QListWidgetItem *item)
{
//    item->listWidget()->takeItem(item->listWidget()->row(item));
    int row = item->listWidget()->row(item);
    show_manga(&this->manga_list.at(row));
}


void MainWindow::on_Options_clicked()
{
    ui->Pages->setHidden(!ui->Pages->isHidden());
}


void MainWindow::on_pushButton_2_clicked()
{
    show_manga(0);
}

void MainWindow::show_manga(Manga* manga)
{
    ui->MainView->hide();
    connect(viewer, &MangaViewer::signal_close, this, [this]{
        this->ui->MainView->show();
    });
    viewer->setManga(manga);
    viewer->show();
}

mangaviewer.cpp:

#include "mangaviewer.h"
#include "ui_mangaviewer.h"

MangaViewer::MangaViewer(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::MangaViewer)
{
    ui->setupUi(this);
    this->setParent(parent);
    this->manga = new Manga{
        .id = "",
        .title = ""
    };

    ui->image->setPixmap(QPixmap("notfound.jpg"));
}

MangaViewer::~MangaViewer()
{
    delete manga;
    delete ui;
}

void MangaViewer::on_pushButton_clicked()
{
    emit signal_close();
    close();
}

Manga *MangaViewer::getManga() const
{
    return manga;
}

void MangaViewer::setManga(Manga *newManga)
{
    if (!(newManga == nullptr)) manga = newManga;
    else {manga->id = ""; manga->title = "";}
    ui->title_label->setText(manga->title.c_str());
}

void MangaViewer::on_read_button_clicked()
{
    emit signal_close();
    close();
}

Christian Ehrlicher

You have to add your widget to the parents layout.