widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QTimer>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
protected:
    void paintEvent(QPaintEvent *);
    void numAdd();
private slots:
    void on_upBtn_clicked();

    void on_rightBtn_clicked();

    void on_leftBtn_clicked();

    void on_downBtn_clicked();

private:
    Ui::Widget *ui;
    QTimer *timer;
    int length;
    int angle;
    int xlength;
    int ylength;
};

#endif // WIDGET_H
 

main.cpp

#include"widget.h"

#include<QApplication>

intmain(intargc,char*argv[])

{

QApplicationa(argc,argv);

Widgetw;

w.show();

returna.exec();

}

widget.cpp

#include"widget.h"

#include"ui_widget.h"

#include<QPainter>

#include<QPen>

#include<QBrush>

#include<QConicalGradient>

Widget::Widget
 
(QWidget*parent):

QWidget(parent),

ui(newUi::Widget)

{

ui->setupUi(this);

//設定button和鍵盤連線

ui->upBtn->setShortcut(Qt::Key_Up);

ui->downBtn->setShortcut(Qt::Key_Down);

ui->leftBtn->setShortcut(Qt::Key_Left);

ui->rightBtn->setShortcut(Qt::Key_Right);

this->resize(1080,720);

timer=newQTimer
 
(this);

timer->start(1000);

//update函式的作用就是去呼叫重繪處理函式

connect(timer,SIGNAL(timeout()),this,SLOT(update()));

connect(timer,SIGNAL(timeout()),this,SLOT(numAdd()));

length=0;

angle=0;

xlength=0;

ylength=0;

}

Widget::~Widget()

{

deleteui;

}

voidWidget::paintEvent(QPaintEvent*)

{

QPainterp(this);

QPenpen;

pen.setWidth(5);

pen.setColor(Qt::black);

p.setPen(pen);

QConicalGradientcon(QPoint(0,0),0);

con.setColorAt(0,Qt::white);

con.setColorAt(60.0/360,Qt::red);

con.setColorAt(120.0/360,Qt::yellow);

con.setColorAt(180.0/360,Qt::blue);

con.setColorAt(240.0/360,Qt::green);

con.setColorAt(300.0/360,Qt::black);

con.setColorAt(1.0,Qt::cyan);

QBrushbrush(con);

p.setBrush(brush);

p.drawLine(0,250,this->width(),250);

p.translate(QPoint(length+50+xlength,200+ylength));

p.rotate(angle);

p.drawEllipse(QPoint(0,0),50,50);

/*//儲存原來的設定

p.save();

pen.setColor(Qt::red);

p.setPen(pen);

p.drawLine(0,300,this->width(),300);

//恢復原來的設定

p.restore();

p.drawLine(0,100,this->width(),100);*/

}

voidWidget::numAdd()

{

length+=6;

angle+=6;

if(length>=this->width())

{

length=-100;

}

}

voidWidget::on_upBtn_clicked()

{

ylength-=10;

//update（）每次呼叫都可以啟動重繪

update();

}

voidWidget::on_rightBtn_clicked()

{

xlength+=10;

update();

}

voidWidget::on_leftBtn_clicked()

{

xlength-=10;

update();

}

voidWidget::on_downBtn_clicked()

{

ylength+=10;

update();

}

ui介面

下面是效果圖

學到的東西， 每按一次button    就啟動一次槽函式，然後利用update（）呼叫一次重繪。每按一次button，就呼叫一次重繪來重新畫出小球。