Qt/C++ - Tutorial 086. Using QSequentialAnimationGroup and QPropertyAnimation to move a button

QSequentialAnimationGroup, cpp, Qt, C++, QPropertyAnimation

Let's write a small example of an application in which a button will be moved using property animations. To do this, we use the QSequentialAnimationGroup and QPropertyAnimation classes.

QSequentialAnimationGroup is a class that combines several animations into one group, which allows you to automatically start one animation when the previous QPropertyAnimation has completed.

Animation will be launched by pressing the button and this button will move in the window as shown in the image.

We will create the project by default in Qt Creator, and all changes will apply only to the Widget class. You will need to add a QPushButton button through a graphic designer.

Widget.h

And here is an example in the code

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

#include <QSequentialAnimationGroup>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

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

private slots:
    void onClickButton();

private:
    Ui::Widget *ui;

    // Button animation group
    QSequentialAnimationGroup* animationGroup;
};

#endif // WIDGET_H

Widget.cpp

The important point is that we create QPropertyAnimation with an indication of the property that we want to animate. In this case, it is "geometry". A property can be animated if it is declared in a class as Q_PROPERTY. Then smooth change of values of this property is performed.

#include "widget.h"
#include "ui_widget.h"

#include <QPropertyAnimation>
#include <QDebug>

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);

    // Create an animation group
    animationGroup = new QSequentialAnimationGroup(this);

    // Create an animation of the motion property from left-top to right-top.
    QPropertyAnimation* leftTopToRightTop = new QPropertyAnimation(ui->pushButton, "geometry");
    leftTopToRightTop->setDuration(1000); // Animation duration
    leftTopToRightTop->setStartValue(ui->pushButton->geometry()); // Starting position and animation geometry
    leftTopToRightTop->setEndValue(ui->pushButton->geometry().translated(100, 0)); // End position and geometry of animation
    animationGroup->addAnimation(leftTopToRightTop); // Add animation to the group

    // Right-top Bottom-right
    QPropertyAnimation* rightTopToRightBottom = new QPropertyAnimation(ui->pushButton, "geometry");
    rightTopToRightBottom->setDuration(1000);
    rightTopToRightBottom->setStartValue(leftTopToRightTop->endValue());
    rightTopToRightBottom->setEndValue(leftTopToRightTop->endValue().toRect().translated(0, 100));
    animationGroup->addAnimation(rightTopToRightBottom);

    // Bottom right to left down
    QPropertyAnimation* rightBottomToLeftBottom = new QPropertyAnimation(ui->pushButton, "geometry");
    rightBottomToLeftBottom->setDuration(1000);
    rightBottomToLeftBottom->setStartValue(rightTopToRightBottom->endValue());
    rightBottomToLeftBottom->setEndValue(rightTopToRightBottom->endValue().toRect().translated(-100, 0));
    animationGroup->addAnimation(rightBottomToLeftBottom);

    // Left-bottom top-left
    QPropertyAnimation* leftBottomToLeftTop = new QPropertyAnimation(ui->pushButton, "geometry");
    leftBottomToLeftTop->setDuration(1000);
    leftBottomToLeftTop->setStartValue(rightBottomToLeftBottom->endValue());
    leftBottomToLeftTop->setEndValue(rightBottomToLeftBottom->endValue().toRect().translated(0, -100));
    animationGroup->addAnimation(leftBottomToLeftTop);

    // We connect button pressing to the slot to the button handler.
    connect(ui->pushButton, &QPushButton::clicked, this, &Widget::onClickButton);
}

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

void Widget::onClickButton()
{
    // Run the animation
    animationGroup->start();
}

Conclusion

Thus, it is possible to configure the most varied animations for object properties, which are marked with the Q_PROPERTY macro and have set and get methods.

Git Repository Link