Draw a line animation

[wysota]

The code looks fine (more or less). The problem has to be elsewhere (e.g. the event loop not working).

[ZsCosa]

I think its the loop too but it was only thing i can think of, any suggestion how I can fix them or do it differently ?

[wysota]

Sure. Declare a property (of type QPointF) in your dialog class that will control the end point of the line. Then use QPropertyAnimation to animate that property.

class Dialog : public QDialog {
  Q_OBJECT
  Q_PROPERTY(QPointF endPoint READ endPoint WRITE setEndPoint)
public:
// ...
  QPointF endPoint() const { ... }
public slots:
  void setEndPoint(const QPointF &pt) {
    QLineF l = line->line();
    l.setP2(pt);
    line->setLine(l);
  }
};
 
// ...
 
QPropertyAnimation *anim = new QPropertyAnimation(&dialog, "endPoint");
anim->setStartValue(...);
anim->setEndValue(...);
anim->setDuration(...);
anim->start();

class Dialog : public QDialog {
  Q_OBJECT
  Q_PROPERTY(QPointF endPoint READ endPoint WRITE setEndPoint)
public:
// ...
  QPointF endPoint() const { ... }
public slots:
  void setEndPoint(const QPointF &pt) {
    QLineF l = line->line();
    l.setP2(pt);
    line->setLine(l);
  }
};

// ...

QPropertyAnimation *anim = new QPropertyAnimation(&dialog, "endPoint");
anim->setStartValue(...);
anim->setEndValue(...);
anim->setDuration(...);
anim->start();

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Remember to run the event loop.

[ZsCosa]

I'VE DONE IT! I think what was not needed here is subclassing QGraphicsLineItem so I removed it then just add simple QGraphicsLineItem to the scene and using your above function to edit the endPoint and it worked. Much simpler, maybe I made it more complex then needed.

Thanks very much for you patience with me on this problem, I've learnt alot.

I've attached a working version in case someone ever need it.
dialog.h

#ifndef DIALOG_H
#define DIALOG_H
 
#include <QDialog>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QTimer>
#include <QGraphicsLineItem>
 
 
 
namespace Ui {
class Dialog;
}
 
class Dialog : public QDialog
{
    Q_OBJECT
    Q_PROPERTY(QPointF endPoint READ endPoint WRITE setEndPoint)
 
public:
    explicit Dialog(QWidget *parent = 0);
    ~Dialog();
    QPointF endPoint() const;
public slots:
    QPointF setEndPoint(const QPointF &pt);
private:
    Ui::Dialog *ui;
    QGraphicsScene *scene;
    QTimer *timer;
    QGraphicsLineItem *myLine;
};
 
#endif // DIALOG_H

#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QTimer>
#include <QGraphicsLineItem>



namespace Ui {
class Dialog;
}

class Dialog : public QDialog
{
    Q_OBJECT
    Q_PROPERTY(QPointF endPoint READ endPoint WRITE setEndPoint)

public:
    explicit Dialog(QWidget *parent = 0);
    ~Dialog();
    QPointF endPoint() const;
public slots:
    QPointF setEndPoint(const QPointF &pt);
private:
    Ui::Dialog *ui;
    QGraphicsScene *scene;
    QTimer *timer;
    QGraphicsLineItem *myLine;
};

#endif // DIALOG_H

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dialog.cpp

#include "dialog.h"
#include "ui_dialog.h"
 
 
#include <QGraphicsView>
#include <QPropertyAnimation>
 
Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);
 
    scene = new QGraphicsScene(this);
 
    ui->graphicsView->setScene(scene);
    ui->graphicsView->setSceneRect(0,0,300,300);
    ui->graphicsView->setRenderHint(QPainter::Antialiasing);
 
    myLine = new QGraphicsLineItem(0,0,10,10);
    myLine->setPen(QPen(Qt::red, 5, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
 
 
    scene->addItem(myLine);
 
    QPropertyAnimation *anim = new QPropertyAnimation(this, "endPoint");
    anim->setStartValue(QPointF(50,50));
    anim->setEndValue(QPointF(200,200));
    anim->setDuration(1000);
    anim->start();
 
 
}
 
Dialog::~Dialog()
{
    delete ui;
}
 
QPointF Dialog::endPoint() const
{
    QLineF l = myLine->line();
    return l.p2();
}
 
QPointF Dialog::setEndPoint(const QPointF &pt)
{
    QLineF l = myLine->line();
    l.setP2(pt);
    myLine->setLine(l);
}

#include "dialog.h"
#include "ui_dialog.h"


#include <QGraphicsView>
#include <QPropertyAnimation>

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

    scene = new QGraphicsScene(this);

    ui->graphicsView->setScene(scene);
    ui->graphicsView->setSceneRect(0,0,300,300);
    ui->graphicsView->setRenderHint(QPainter::Antialiasing);

    myLine = new QGraphicsLineItem(0,0,10,10);
    myLine->setPen(QPen(Qt::red, 5, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));


    scene->addItem(myLine);

    QPropertyAnimation *anim = new QPropertyAnimation(this, "endPoint");
    anim->setStartValue(QPointF(50,50));
    anim->setEndValue(QPointF(200,200));
    anim->setDuration(1000);
    anim->start();


}

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

QPointF Dialog::endPoint() const
{
    QLineF l = myLine->line();
    return l.p2();
}

QPointF Dialog::setEndPoint(const QPointF &pt)
{
    QLineF l = myLine->line();
    l.setP2(pt);
    myLine->setLine(l);
}

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