c++ - 在一个类中填充一个QGraphicsScene并返回场景指针

Question

我正在实现一个用我的图形项目填充场景的类。我想从我的类(class)返回一个指向场景的指针到主窗口。但是由于某种原因，当我尝试这样做时，图形 View 没有显示任何内容。如果填充功能在主窗口中，则填充功能正常工作。

如何将函数保留在类中并将场景指针返回到主窗口？

这是我的类(class)标题:

#ifndef KEYBOARD_H
#define KEYBOARD_H
#include <QGraphicsScene>
#include <QVector>
#include <pianokey.h>


class keyboard
{
public:
    keyboard(QObject *parent);
    void highLightKeys(QVector<int> highVec);
    void resetHighLight();
    QGraphicsScene* getScene() {return scene;}
    /*~keyboard()
    {
        while(!vec.empty())
        {
            delete vec.back();
            vec.pop_back();
        }
    }*/



private:
    QGraphicsScene* scene;
    QVector<QSharedPointer<pianoKey> > vec;
};

#endif // KEYBOARD_H

这是 cpp:

#include "keyboard.h"
#include "pianokey.h"
#include <QVector>
#include <QSharedPointer>

keyboard::keyboard(QObject * parent)
{
        scene=new QGraphicsScene(parent);
        vec.resize(14);
        int black[]{2,4,7,9,11,14,16,19,21,23};
        for(int i=0; i<14;i++)
        {
            QSharedPointer<pianoKey> temp(new pianoKey(i*WHITE_WIDTH,0));
            scene->addItem(temp.data());
            vec[i]=temp;
        }
        //PLEASE DON'T JUDGE ME ON THIS I SWEAR I'LL THINK OF SOMETHING
        QSharedPointer<pianoKey> black1(new pianoKey(true,25,0));
        scene->addItem(black1.data());
        vec.insert(2,black1);
        QSharedPointer<pianoKey> black2(new pianoKey(true,55,0));
        scene->addItem(black2.data());
        vec.insert(4,black2);
        QSharedPointer<pianoKey> black3(new pianoKey(true,115,0));
        scene->addItem(black3.data());
        vec.insert(7,black3);
        QSharedPointer<pianoKey> black4(new pianoKey(true,145,0));
        scene->addItem(black4.data());
        vec.insert(9,black4);
        QSharedPointer<pianoKey> black5(new pianoKey(true,175,0));
        scene->addItem(black5.data());
        vec.insert(11,black5);
        QSharedPointer<pianoKey> black6(new pianoKey(true,235,0));
        scene->addItem(black6.data());
        vec.insert(14,black6);
        QSharedPointer<pianoKey> black7(new pianoKey(true,265,0));
        scene->addItem(black7.data());
        vec.insert(16,black7);
        QSharedPointer<pianoKey> black8(new pianoKey(true,325,0));
        scene->addItem(black8.data());
        vec.insert(19,black8);
        QSharedPointer<pianoKey> black9(new pianoKey(true,355,0));
        scene->addItem(black9.data());
        vec.insert(21,black9);
        QSharedPointer<pianoKey> black10(new pianoKey(true,385,0));
        scene->addItem(black10.data());
        vec.insert(23,black10);

}

void keyboard::highLightKeys(QVector<int> highVec)
{
    for(int i=0; i<highVec.size();i++)
    {
        int tempInt = highVec[i];
        vec[tempInt]->highlight();

    }
}

void keyboard::resetHighLight()
{
    for(int i=0;i<vec.size();i++)
        vec[i]->resetHighlight();
}

更新:也发布我的主窗口代码:

标题:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QGraphicsScene>
namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Ui::MainWindow *ui;
    QGraphicsScene *scene;
    void testfunc();

};

#endif // MAINWINDOW_H

CPP:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "pianokey.h"
#include "keyboard.h"


MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    keyboard piano(this);
    scene = piano.getScene();
    ui->graphicsView->setScene(scene);


}

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

Answer 1

问题是在 MainWindow 的构造函数中，您在堆栈上创建了一个 keyboard。在这个构造函数的最后，调用了keyboard的析构函数，因为你使用的是智能指针，它会析构所有的new pianoKey(..);，因此删除他们从现场。 (这是因为 Qt 很聪明，当您在 QGraphicsSceneItem 上调用 delete 时，它会在释放内存之前将其从场景中删除)

只需使用:

QVector<pianoKey*> vec;

无论如何删除场景时，所有项目都会被智能删除，因此在这种特定情况下不建议使用智能指针。