Change page of QstackedWidget with animation

Question

I want to be able to change page of QStackedWidget with some kind of animation (like fade in/out or others...)
after some research I find out maybe its possible with QGraphicsOpacityEffect, then I found this codes in here

Fade In Your Widget

// w is your widget
QGraphicsOpacityEffect *eff = new QGraphicsOpacityEffect(this);
w->setGraphicsEffect(eff);
QPropertyAnimation *a = new QPropertyAnimation(eff,"opacity");
a->setDuration(350);
a->setStartValue(0);
a->setEndValue(1);
a->setEasingCurve(QEasingCurve::InBack);
a->start(QPropertyAnimation::DeleteWhenStopped);

Fade Out Your Widget

// w is your widget
QGraphicsOpacityEffect *eff = new QGraphicsOpacityEffect(this);
w->setGraphicsEffect(eff);
QPropertyAnimation *a = new QPropertyAnimation(eff,"opacity");
a->setDuration(350);
a->setStartValue(1);
a->setEndValue(0);
a->setEasingCurve(QEasingCurve::OutBack);
a->start(QPropertyAnimation::DeleteWhenStopped);
connect(a,SIGNAL(finished()),this,SLOT(hideThisWidget()));
// now implement a slot called hideThisWidget() to do
// things like hide any background dimmer, etc.

but looks like these codes have some problem when used in QWidget inside of QStackedWidget i mean widget successfully fade in and out, but after animation finish if I minimize the windows the widget will disappear completely! (Im still able to see widget in bottom right corner of my window, looks like its pos changed?!)
btw my program is frameless.
thanks for help.

here is a example from my problem
test.cpp

Test::Test(QWidget *parent)
    : CustomMainWindow(parent)
{
    ui.setupUi(this);

    setShadow(ui.bg_app);

    connect(ui.close_app_btn, &QPushButton::clicked, this, &QWidget::close);
    connect(ui.minimize_app_btn, &QPushButton::clicked, this, &QWidget::showMinimized);

    QGraphicsOpacityEffect* eff = new QGraphicsOpacityEffect(this);
    ui.checking->setGraphicsEffect(eff); // checking is my widget inside of QStackedWidget.
    QPropertyAnimation* a = new QPropertyAnimation(eff, "opacity");
    a->setDuration(350);
    a->setStartValue(0);
    a->setEndValue(1);
    a->setEasingCurve(QEasingCurve::InBack);
    a->start(QPropertyAnimation::DeleteWhenStopped);
}

CustomMainWindow.cpp

CustomMainWindow::CustomMainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    setWindowFlags(windowFlags() | Qt::Window | Qt::FramelessWindowHint | Qt::WindowSystemMenuHint);
    setAttribute(Qt::WA_TranslucentBackground);
}

void CustomMainWindow::setShadow(QWidget* window)
{
    QGraphicsDropShadowEffect* windowShadow = new QGraphicsDropShadowEffect;
    windowShadow->setBlurRadius(9.0);
    windowShadow->setColor(palette().color(QPalette::Highlight));
    windowShadow->setOffset(0.0);
    window->setGraphicsEffect(windowShadow);
}

when I run my program with this code, at first its successfully Fade In, but if I for example minimize the window the widget move from its original position to somewhere else, look at this gif

Answer 1

Note: MainWindow is the name of my class.

Header file:

//...
private slots:
    void animationStackedWidgets();

    void whenAnimationFinish();
//....

CPP file:

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->button, &QPushButton::clicked, this, &MainWindow::animationStackedWidgets);
}

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

void MainWindow::animationStackedWidgets()
{
    QGraphicsOpacityEffect *effect = new QGraphicsOpacityEffect(this);
    ui->stackedWidget->setGraphicsEffect(effect);
    QPropertyAnimation *anim = new QPropertyAnimation(effectSw,"opacity");
    anim->setDuration(350);
    anim->setStartValue(0);
    anim->setEndValue(1);
    anim->setEasingCurve(QEasingCurve::InBack);
    anim->start(QPropertyAnimation::DeleteWhenStopped);

    connect(anim, SIGNAL(finished()), this, SLOT(whenAnimationFinish()));
}

void MainWindow::whenAnimationFinish()
{
    ui->stackedWidget->setGraphicsEffect(0); // remove effect
}