Program Crashed using QGridLayout

[Chanchan]

Hey there ! I have a problem using QGridLayout. Here is what I want to implement :

I want to create a program recovering a video from an Ip Camera AND The geolocalization of this camera. So I already have two working program, the video recovering from the camera and the map widget thanks to Marble.

Now I want to integrate both of them in the same project. In order to lock their position I planned to use QGridLayout. So I created this layout and I first wanted to put the video on it, but it crashed and I dont understand why, so here is my code :
Fen.pro

SOURCES += \
    main.cpp \
    mafenetre.cpp
QT += core gui
QT += widgets


QT += multimedia multimediawidgets

HEADERS += \
    mafenetre.h


TEMPLATE = app

CONFIG += qt

Fenetre.h

#ifndef MAFENETRE_H
#define MAFENETRE_H

#include <QtWidgets>

#include <QtMultimedia>
#include <QtMultimediaWidgets>

class MaFenetre : public QWidget
{
    Q_OBJECT
public:
    explicit MaFenetre(QWidget *parent = 0);
    ~MaFenetre();

private:
      QMediaPlaylist *playlist;
      QMediaPlayer *player;
      QVideoWidget *videoWidget;

signals:

public slots:
    void stateChanged(QMediaPlayer::State state);
    void metaDataChanged();
    void metaDataChanged(const QString &key, const QVariant &value);
    void error(QMediaPlayer::Error error);
};

#endif // MAFENETRE_H

Fenetre.cpp

#include "mafenetre.h"
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsVideoItem>
#include <QDebug>

MaFenetre::MaFenetre(QWidget *parent) :
    QWidget(parent)
{
    //QString fichier = QCoreApplication::applicationDirPath() + QString("/test.mpg");
    qDebug() << QUrl("rtsp://root:thales@169.254.162.23/axis-media/media.amp");


    player = new QMediaPlayer;
    player->setMedia(QUrl("rtsp://root:xxxxxxx@169.254.xxxx.xx/axis-media/media.amp"));

    // GUI 1
    QVBoxLayout *layoutPrincipal = new QVBoxLayout;
    videoWidget = new QVideoWidget(this);
    layoutPrincipal->addWidget(videoWidget);
    player->setVideoOutput(videoWidget);
    setLayout(layoutPrincipal);


    setWindowTitle(QString::fromUtf8("player"));
    //setFixedWidth(960);
    //setFixedHeight(540);


    connect(player, SIGNAL(stateChanged(QMediaPlayer::State)), this, SLOT(stateChanged(QMediaPlayer::State)));
    //connect(player, SIGNAL(metaDataChanged()), this, SLOT(metaDataChanged()));
    connect(player, SIGNAL(metaDataChanged(const QString &, const QVariant &)), this, SLOT(metaDataChanged(const QString &, const QVariant &)));
    connect(player, SIGNAL(error(QMediaPlayer::Error)), this, SLOT(error(QMediaPlayer::Error)));

    player->play();
}

MaFenetre::~MaFenetre()
{

}

void MaFenetre::stateChanged(QMediaPlayer::State state)
{
    qDebug() << Q_FUNC_INFO << state;
    /*if (state == QMediaPlayer::StoppedState)
    {
        videoWidget->update();
    }*/
}

void MaFenetre::metaDataChanged()
{
    qDebug() << player->availableMetaData();
    if (player->isMetaDataAvailable())
    {
        qDebug() << player->metaData(QMediaMetaData::Title).toString();
        qDebug() << player->metaData(QMediaMetaData::Size);
        qDebug() << player->metaData(QMediaMetaData::Duration);
        qDebug() << player->metaData(QMediaMetaData::Resolution);
    }
}

void MaFenetre::metaDataChanged(const QString &key, const QVariant &value)
{
    // "AudioBitRate", "AudioCodec", "PixelAspectRatio", "Resolution", "VideoCodec"
    if(key == "AudioCodec")
        qDebug() << key << value;
    if(key == "VideoCodec")
        qDebug() << key << value;
    if(key == "Resolution")
        qDebug() << key << value;
}

void MaFenetre::error(QMediaPlayer::Error error)
{
    qDebug() << Q_FUNC_INFO << player->errorString() << error;
}

main.cpp

#include <QApplication>
#include <QWidget>
#include "mafenetre.h"
//#include <marble/MarbleWidget.h>
#include <QGridLayout>




int main(int argc, char *argv[])

{

    QApplication app(argc, argv);

   

    QWidget fenprincip;
    //fenprincip.setFixedSize(1600,900);
    MaFenetre *video;//(&fenprincip);

    // Création du Layout Grid :
    QGridLayout *layout = new QGridLayout;
    layout->addWidget(video, 0,0);
    

    fenprincip.setLayout(layout);//On indique à la fenetre d'utiliser le layout grid

    fenprincip.show();


    return app.exec();

}

And this is my error :
Starting /home/thales/build-Fenetre-Desktop-Debug/Fenetre...
QLayout: Cannot add a null widget to QGridLayout/
/home/thales/build-Fenetre-Desktop-Debug/Fenetre exited with code 0

If someone can help me it would be lovely :D Thank you :)

[Christian Ehrlicher]

@Chanchan said in Program Crashed using QGridLayout:

layout->addWidget(video, 0,0);

video pointer is uninitialized so what do you expect?

[JonB]

@Chanchan

    MaFenetre *video;//(&fenprincip);

    // Création du Layout Grid :
    QGridLayout *layout = new QGridLayout;
    layout->addWidget(video, 0,0);

video is not set to anything, and happens to be "null". You then try to add that to your QGridLayout. Hence QLayout: Cannot add a null widget to QGridLayout/.

[Chanchan]

Oh I see... Ehm so how should I modify this to create a widget from that video. I have to initialized it in my main I guess ?

(thanks for your fast answer :) )

[JonB]

@Chanchan
Purely at a guess, since I don't claim to know what is going on in your code. MaFenetre *video; simply creates a pointer to a MaFenetre widget, but does not create a MaFenetre instance nor point to one. You probably intend one of:

MaFenetre video;
layout->addWidget(&video, 0,0);

or

MaFenetre *video = new MaFenetre;
layout->addWidget(video, 0,0);

[Chanchan]

Ok ok I think I got it, i will try with it, thank you for your help, I will come back when I will succeed to make this work ;)
thank you again :D

[Chanchan]

@JonB Your second solution worked perfectly so thank you very much <3 I put "solved" on the subject :)