如何在 QScrollArea 上绘制一个选择矩形？

Question

我创建了一个图像查看器应用程序，它可以打开和保存图像并将图像加载到 QLabel 上，然后我创建了一个 ScrollArea 来滚动大图像，在我的第二步中我试图绘制一个 selection矩形到select一个特定的子区域，我绘制selection矩形的步骤如下：

1- 我使用了 PaintEvent 来绘制矩形。 2- 我使用 MouseEvent select 子区域。

问题是，当我运行我的代码时，我可以在 QWidget 上绘制矩形，但不能在 ScrollArea 上绘制。

这是我的代码：

在imageviewer.h

class ImageViewer : public QWidget{
Q_OBJECT
public:
   explicit ImageViewer(QWidget *parent = 0);
   ~ImageViewer();
private:
   Ui::ImageViewer *ui;

private slots:
  void on_openButton_pressed();

  void on_saveButton_pressed();

private:
  QPixmap image;
  QImage *imageObject;
  bool selectionStarted;
  QRect selectionRect;
  QMenu contextMenu;

protected:
  void paintEvent(QPaintEvent *e);
  void mousePressEvent(QMouseEvent *e);
  void mouseMoveEvent(QMouseEvent *e);
  void mouseReleaseEvent(QMouseEvent *e);
};

这是imageviewer.cpp

ImageViewer::ImageViewer(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::ImageViewer)
{
    ui->setupUi(this);
    ui->scrollArea->setWidget(ui->imageLabel);
}

打开和保存功能：

void ImageViewer::on_openButton_pressed()
{
    QString imagePath = QFileDialog::getOpenFileName(this, tr("Open File") , "" ,
                                                 tr("JPEG (*.jpg *.jpeg);;PNG (*.png);;BMP (*.bmp)"));

    imageObject = new QImage();
    imageObject->load(imagePath);

    image = QPixmap::fromImage(*imageObject);

    ui->imageLabel->setPixmap(image);
    ui->imageLabel->adjustSize();

}

void ImageViewer::on_saveButton_pressed()
{
    QString imagePath = QFileDialog::getSaveFileName(this, tr("Save File") , "" ,
                                                 tr("JPEG (*.jpg *.jpeg);;PNG (*.png);;BMP (*.bmp)"));

    *imageObject = image.toImage();
    imageObject->save(imagePath);
}

绘图和鼠标事件函数：

void ImageViewer::paintEvent(QPaintEvent *e){
    QWidget::paintEvent(e);
    QPainter painter(this);
    painter.setPen(QPen(QBrush(QColor(0,0,0,180)),1,Qt::DashLine));
    painter.setBrush(QBrush(QColor(255,255,255,120)));
    painter.drawRect(selectionRect);
}

void ImageViewer::mousePressEvent(QMouseEvent *e){
    if(e->button() == Qt::RightButton){
        if(selectionRect.contains(e->pos()))
            contextMenu.exec(this->mapToGlobal(e->pos()));
    }
    else{
        selectionStarted = true;
        selectionRect.setTopLeft(e->pos());
        selectionRect.setBottomRight(e->pos());
    }
}

void ImageViewer::mouseMoveEvent(QMouseEvent *e){
    if(selectionStarted){
        selectionRect.setBottomRight(e->pos());
        repaint();
    }
}

void ImageViewer::mouseReleaseEvent(QMouseEvent *e){
    selectionStarted = false;
}

这是我的应用程序的屏幕截图

Answer 1

How can I draw a selection rectangle on QScrollArea?

您需要 QRubberBand which supposed to be directly applied to ui->imageLabel widget you use to display an image you want to scroll. Whether or not you should overload QLabel for ui->imageLabel is a question of implementation. Please see the example 鼠标事件，当然最好将其应用于您的标签图像 class。

我从代码的外观上了解到您使用了 Qt Designer？这使覆盖该标签 class 变得复杂，但您可以不使用 .ui 文件或使用 event filter 来捕获给定对象的所有事件。

当然，您目前拥有的东西最终可以打磨得足以满足实际使用。它只会让你付出更多的努力。您可以避免重载 paintEvent 等，关键是在需要应用的地方直接应用正确的方法。

// the example applied to authors code as requested
class MyImageLabel : public QLabel
{
public:
   explicit MyImageLabel(QWidget *parent = 0) : QLabel(parent), rubberBand(0) {}
private:
   QRubberBand* rubberBand;
   QPoint origin;

   void mousePressEvent(QMouseEvent *event);
   void mouseMoveEvent(QMouseEvent *event);
   void mouseReleaseEvent(QMouseEvent *event)
};

void MyImageLabel::mousePressEvent(QMouseEvent *event)
{
    origin = event->pos();
    if (!rubberBand)
        rubberBand = new QRubberBand(QRubberBand::Rectangle, this);
    rubberBand->setGeometry(QRect(origin, QSize()));
    rubberBand->show();
}

void MyImageLabel::mouseMoveEvent(QMouseEvent *event)
{
    rubberBand->setGeometry(QRect(origin, event->pos()).normalized());
}

void MyImageLabel::mouseReleaseEvent(QMouseEvent *event)
{
    rubberBand->hide();
    // determine selection, for example using QRect::intersects()
    // and QRect::contains().
}

ImageViewer::ImageViewer(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::ImageViewer)
{
    ui->setupUi(this);
    // resolve this better than:
    delete ui->imageLabel; // you already have the QLabel object here?
    ui->imageLabel = new MyImageLabel;
    ui->scrollArea->setWidget(ui->imageLabel);
}

如何在 QScrollArea 上绘制一个选择矩形？

How can I draw a selection rectangle on QScrollArea?

c++

qt

qscrollarea