QFrame Border Does Not Draw

kendavistoo

I am including a simple example which has a MainWindow, and two classes, ClassAFrame and ClassBFrame, which inherit QFrame. The MainWindow establishes an instance of each of the classes. Both have style QFrame::Box | QFrame::Raised with a linewidth of 3. ClassAFrame contains a paintEvent function while ClassBFrame does not. MainWindow draws the frame of ClassBFrame correctly but does not draw the frame of ClassAFrame. What am I doing wrong?

classaframe.h:

#ifndef CLASSAFRAME_H
#define CLASSAFRAME_H

#include "QFrame"
#include <QPainter>

class ClassAFrame : public QFrame
{
public:
    ClassAFrame(QWidget *parent = nullptr, Qt::WindowFlags f = Qt::Widget);

protected:
    void paintEvent(QPaintEvent*);
};

#endif // CLASSAFRAME_H

classbframe.h:

#ifndef CLASSBFRAME_H
#define CLASSBFRAME_H

#include <QFrame>
#include <QPainter>

class ClassBFrame : public QFrame
{
public:
    ClassBFrame(QWidget *parent = nullptr, Qt::WindowFlags f = Qt::Widget);
};

#endif // CLASSBFRAME_H

mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <classaframe.h>
#include <classbframe.h>
#include <QPushButton>
#include <QPainter>

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

    QPushButton* buttonM;
    QPushButton* buttonA;

    ClassAFrame* aFrame;
    ClassBFrame* bFrame;

protected:
    void paintEvent(QPaintEvent*);

public slots:
    void SlotHandleClickMain();
    void SlotHandleClickAFrame();
};

#endif // MAINWINDOW_H

classaframe.cpp:

#include "classaframe.h"

ClassAFrame::ClassAFrame(QWidget *parent, Qt::WindowFlags f) : QFrame(parent, f)
{
}

void ClassAFrame::paintEvent(QPaintEvent*){
    QPainter* painter = new QPainter(this);
    int x = 20 + (int)(50 + (rand() % 20));
    int y = (this->height() - 40);
    QRect myRect(x,y,12,12);
    painter->fillRect(myRect, Qt::blue);
    delete painter;
}

classbframe.cpp:

#include "classbframe.h"

ClassBFrame::ClassBFrame(QWidget *parent, Qt::WindowFlags f) : QFrame(parent, f)
{
}

main cpp:

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainwindow.cpp:

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    buttonM = new QPushButton("Update Main", this);
    connect(buttonM, &QPushButton::clicked, this, &MainWindow::SlotHandleClickMain);

    buttonA = new QPushButton("Update AFrame", this);
    connect(buttonA, &QPushButton::clicked, this, &MainWindow::SlotHandleClickAFrame);

    aFrame = new ClassAFrame(this, Qt::Widget);
    bFrame = new ClassBFrame(this, Qt::Widget);

    this->setGeometry (10, 100, 500, 500);
    buttonM->setGeometry(30, 20, 120, 24);
    buttonA->setGeometry(230, 20, 120, 24);

    aFrame->setGeometry( 30, 130, 300, 100);
    bFrame->setGeometry( 30, 260, 300, 100);

    aFrame->setFrameStyle(QFrame::Box | QFrame::Raised);
    bFrame->setFrameStyle(QFrame::Box | QFrame::Raised);

    aFrame->setLineWidth(3);
    bFrame->setLineWidth(3);

    aFrame->setVisible(true);
    bFrame->setVisible(true);
}

MainWindow::~MainWindow()
{
}

void MainWindow::SlotHandleClickMain(){
    this->update();
}

void MainWindow::SlotHandleClickAFrame(){
    aFrame->update();
}

void MainWindow::paintEvent(QPaintEvent*){

    QPainter* painter = new QPainter(this);
    int x = 20 + (int)(50 + (rand() % 20));
    int y = (this->height() - 40);
    QRect myRect(x,y,12,12);
    painter->fillRect(myRect, Qt::red);
    delete painter;
}

SGaist

Hi,

You should call the base's class paintEvent and then do your own drawings.

On a side note, there's no need to allocate a QPainter on the heap, keep on the stack, that will simplify your code.