先看效果

UI界面

.h文件

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = nullptr);
    ~Widget();

private slots:
    void slotShowWidget();

private:
    Ui::Widget *ui;
    bool _showFlg; //是否显示了下半部分窗口

};

#endif // WIDGET_H

.cpp

#include "widget.h"
#include <QDebug>
#include "ui_widget.h"
#include <QPropertyAnimation>

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget),
    _showFlg(false)
{
    ui->setupUi(this);
    this->setFixedHeight(100); //设置下半部分窗口隐藏

    connect(ui->btnScale, &QPushButton::clicked, this, &Widget::slotShowWidget);
}

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

void Widget::slotShowWidget()
{
    QPropertyAnimation* animation = new QPropertyAnimation(this, ""); //qt动画类
    animation->setDuration(500); //动画持续时间500ms
    if(!_showFlg){
        ui->btnScale->setIcon(QIcon(tr(":/Image/ArrowUp.png")));
        animation->setStartValue(100);//动画开始值和结束值
        animation->setEndValue(500);
        connect(animation, &QPropertyAnimation::valueChanged, [this](const QVariant& value){
            this->setFixedHeight(value.toInt());
            qDebug()<<value.toInt();
        });
        animation->start(QAbstractAnimation::DeleteWhenStopped);
        _showFlg = true;
    }
    else {
        ui->btnScale->setIcon(QIcon(":/Image/ArrowDown.png"));
        animation->setStartValue(500);
        animation->setEndValue(100);
        connect(animation, &QPropertyAnimation::valueChanged, [this](const QVariant& value){
            this->setFixedHeight(value.toInt());
        });
        animation->start(QAbstractAnimation::DeleteWhenStopped);
        _showFlg = false;
    }
}