如何在Qt上自定义可滚动图像小部件

Question

I have problem to scrollable for my custom image Widget.

This is my custom image Widget.

imagewidget.h:

#ifndef IMAGEWIDGET_H
#define IMAGEWIDGET_H

#include <QWidget>
#include <QImage>
#include <QString>
#include <QPaintEvent>
#include <QAbstractScrollArea>

class ImageWidget: public QWidget
{
public:
    explicit ImageWidget(QWidget *parent = 0);
    QImage m_Image;
    void loadImage(const QString &fileName);
protected:
    void paintEvent(QPaintEvent *event);
};

#endif // IMAGEWIDGET_H

imagewidget.cpp:

#include "imagewidget.h"
#include <QPainter>
#include <QPoint>
#include <QDebug>
#include <QScrollBar>


ImageWidget::ImageWidget(QWidget *parent): QWidget(parent)
{
}

void ImageWidget::loadImage(const QString &fileName)
{
    if(!fileName.isNull()){
        m_Image.load(fileName);
        this->update();
        qDebug()<<"Load Image"<<endl;
    }
}

void ImageWidget::paintEvent(QPaintEvent *event)
{
    QPainter p(this);
    if(!m_Image.isNull()){
        p.drawImage(QPoint(0,0),m_Image);

    }
    qDebug()<<"Paint Event"<<endl;
}

And this is mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QScrollArea>
#include <QString>
#include <QFileDialog>
#include <QWidget>
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow),
    scrollArea(new QScrollArea())
{
    ui->setupUi(this);
    m_Image = new ImageWidget(this);
    scrollArea->setWidgetResizable(true);
    scrollArea->setWidget(m_Image);
    setCentralWidget(scrollArea);
}

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

void MainWindow::on_actionOpen_triggered()
{
   QString fileName = QFileDialog::getOpenFileName(this, tr("Open Image"), "/", tr("Image Files (*.png *.jpg *.bmp *.tif *.tiff)"));

   m_Image->loadImage(fileName);
   m_Image->adjustSize();
   this->update();

}

With a large image, the image cannot diplay with scroll bar. My result is below. Thank you for reading.

Answer 1

You forget to set ImageWidget minimumsize.

void ImageWidget::loadImage(const QString &fileName)
    {
    if(!fileName.isNull()){
        m_Image.load(fileName);
        setMinimumSize(m_Image.size());   //add this line
        this->update();
        qDebug()<<"Load Image"<<endl;
    }
}

ScrollArea shows scrollbars when its size is smaller than content's widget (ImageWidget in this case). You just load image and paint it on widget but not change widget's size.

:) My first answer on stackoverflow.