尝试在 Qt Creator 中绘制，使用对象作为输入

Posted 2023-02-23

【中文标题】尝试在 Qt Creator 中绘制，使用对象作为输入

【英文标题】：Trying to draw in Qt Creator, using an object as an input

【发布时间】：2017-11-27 21:30:35

【问题描述】：

我只是在创建一个简单的程序，它显示汽车对象所在的点，并使用计时器更新该点的位置，以便稍后它可以移动。

我的代码目前只显示 (0, 0) 处的点，我不知道为什么。

我的 mainwindow.cpp：

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <iostream>
#include "twovector.h"
#include "car.h"
#include "vehicle.h"
#include <vector>
#include <QTimer>
#include <QStandardItem>
#include <QPainter>

using namespace std;

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)

    ui->setupUi(this);


    fCar = new Car(TwoVector(150, 2), 4);


    QTimer *timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(paintEvent()));
    // connect(timer, SIGNAL(timeout()), this, SLOT(Drive()));
    timer->start(10);




MainWindow::~MainWindow()

    delete ui;


void MainWindow::Drive()
    fCar->Drive(fCar->GetVelocity());


void MainWindow::paintEvent(QPaintEvent *)

    QPainter painter(this);
    QPen DotPen(Qt::red);
    DotPen.setWidth(10);

    painter.setPen(DotPen);
    //painter.drawPoint(0, 0);

    painter.drawPoint((fCar->GetPosition().GetRadius())*(cos(fCar->GetPosition().GetAngle()))
                      , (fCar->GetPosition().GetRadius())*(sin(fCar->GetPosition().GetAngle())));
        //Draw the dot, where the centre of the window is (0,0)

主窗口头文件：

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "car.h"

namespace Ui 
class MainWindow;


class MainWindow : public QMainWindow

    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

    void Drive();

    void paintEvent(QPaintEvent *);

private:
    Ui::MainWindow *ui;

    Car *fCar;
;

#endif // MAINWINDOW_H

vehicle.ccp（汽车类从中继承）

#include "vehicle.h"
#include "twovector.h"
#include <iostream>
using namespace std;

Vehicle::Vehicle()


Vehicle::Vehicle(TwoVector position, double velocity)
    fPosition = position;
    fVelocity = velocity;


Vehicle::~Vehicle()


void Vehicle::SetValue(string ValueName, double Value) 
    if(ValueName.compare("Radius") == 0)
        fPosition.SetRadius(Value);
    else
        if(ValueName.compare("Angle") == 0)
            fPosition.SetAngle(Value);
        else if(ValueName.compare("Velocity") == 0)
            fVelocity = Value;
        else
            cerr << "Unknown field entered: " << ValueName << endl;
    



void Vehicle::Drive(int velocity)
    fPosition.SetAngle(fPosition.GetAngle() + (velocity)/(fPosition.GetRadius()));

车辆.h：

#ifndef VEHICLE_H
#define VEHICLE_H
#include "twovector.h"
#include <iostream>
using namespace std;

class Vehicle

public:
    Vehicle();

    Vehicle(TwoVector position, double velocity);

    ~Vehicle();

    inline TwoVector GetPosition() return fPosition;

    inline double GetVelocity() return fVelocity;

    inline void SetPosition(TwoVector position) fPosition = position;

    void SetValue(string ValueName, double Value);

    void Drive(int velocity);

private:

    TwoVector fPosition;
    double fVelocity;
;

#endif // VEHICLE_H

双向量.ccp：

#include "twovector.h"

TwoVector::TwoVector()
    fRadius = 0;
    fTheta = 0;


TwoVector::TwoVector(double radius, double theta)
    fRadius = radius;
    fTheta = theta;


TwoVector::~TwoVector()


TwoVector TwoVector::operator +=(TwoVector position1)
    TwoVector position2;
        //Creates a new object which is given a position
    position2.fRadius = sqrt(((fRadius)*(fRadius))+((position1.fRadius)*(position1.fRadius))
                             + 2*((position1.fRadius)*(fRadius))*cos((position1.fTheta)-(fTheta)));
    position2.fTheta = fTheta + atan2((position1.fRadius)*(sin((position1.fTheta)-(fTheta))),
                                 fRadius + (position1.fRadius)*(cos((position1.fTheta)-fTheta)));
    return(position2);
    //New position returned

TwoVector.h：

#ifndef TWOVECTOR_H
#define TWOVECTOR_H
#include <math.h>


class TwoVector 
public:
    TwoVector();

    TwoVector(double radius, double theta);

    ~TwoVector();

    inline double GetX() return fRadius*cos(fTheta);
    inline double GetY() return fRadius*sin(fTheta);
    inline double GetRadius() const return fRadius;
    inline double GetAngle() const return fTheta;
        //Accessor functions, these simply return the value of the coordinates


    inline void SetRadius(double radius) fRadius = radius;
    inline void SetAngle(double theta) fTheta = theta;
    inline void SetRadiusAndAngle(double radius, double theta) 
        fRadius = radius, fTheta = theta;
        //Mutator function to change the position

    TwoVector operator += (TwoVector);
        //Operator overloading so that vectors can be added


private:

    double fRadius;
    double fTheta;

;

#endif // TWOVECTOR_H

汽车.h：

#ifndef CAR_H
#define CAR_H
#include "twovector.h"
#include "vehicle.h"
#include <iostream>
using namespace std;

class Car: public Vehicle 
public:
    Car();

    Car(TwoVector position, double velocity);

    ~Car();

private:

    TwoVector fPositioncar;
    double fVelocitycar;

;

#endif // CAR_H

汽车.cpp：

#include "car.h"

Car::Car()


Car::Car(TwoVector position, double velocity)
    fPositioncar = position;
    fVelocitycar = velocity;


Car::~Car()

任何帮助将不胜感激！

【参考方案1】：

不要直接调用paintEvent方法，你必须通过update()方法来做，并且你想更新位置，建议进行以下修改：

[...]

    QTimer *timer = new QTimer(this);
    //connect(timer, SIGNAL(timeout()), this, SLOT(paintEvent()));
    connect(timer, SIGNAL(timeout()), this, SLOT(Drive()));
    timer->start(10);
[...]

void MainWindow::Drive()
    fCar->Drive(fCar->GetVelocity());
    update();


[...]

另一个问题是你没有调用父级的构造函数：

car.cpp

#include "car.h"

Car::Car():Vehicle()


Car::Car(TwoVector position, double velocity):Vehicle(position, velocity)
    fPositioncar = position;
    fVelocitycar = velocity;


Car::~Car()

velocity 也是 double 类型的值，另一方面 Drive 配置为整数，您必须将其更改为：

vehicle.cpp

[...]
void Vehicle::Drive(double velocity)
    fPosition.SetAngle(fPosition.GetAngle() + (velocity)/(fPosition.GetRadius()));

修改后的完整工程见以下link。

【讨论】：

嗯好的，那么update函数会告诉程序在返回主循环时调用paint事件吗？我想我明白了，但点似乎仍然没有移动，甚至没有从对象的位置开始？

什么是汽车类？你可以分享你的整个项目来帮助你。

汽车类只有一个构造函数和析构函数，并从车辆类继承——目前它有点毫无意义，但它只是为了稍后当我添加不同类型的继承自车辆类别。我会将它添加到主要问题中。

@JonathanParkes 对我来说最简单的方法是通过 github、drive、dropbox 或类似方式共享代码以快速查看错误。

是的，我忘记调用继承的构造函数了...但是当我调用驱动函数时它似乎没有更新？