問題描述

我創(chuàng)建了一個(gè)名為 ImageLabel 的類，它擴(kuò)展了 QLabel.我希望它保持它顯示的圖像的大小比例，無論它有多拉伸.當(dāng)您使窗口變大時(shí)，它工作正常.當(dāng)您嘗試使窗口變小時(shí)，問題就出現(xiàn)了:它不會調(diào)整高度的大小，而是將其拉伸.我該如何解決這個(gè)問題?

I made a class called ImageLabel which extends QLabel. I want it to keep the size ratio of the image that it is displaying no matter how stretched out it is. It works fine when you make the window larger. The problem comes in when you try to make the window smaller: it doesnt resize the height, it leaves it stretched out. How do I fix this?

int ImageLabel::heightForWidth(int width) const {
    int height = (this->size.height()*width)/this->size.width();
    return height;
}

QSize ImageLabel::sizeHint() const {
    return this->size;
}

QSize ImageLabel::minimumSizeHint() const {
    return QSize(0, 0);
}

void ImageLabel::setSizePolicy(){
    QSizePolicy policy = QSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
    policy.setHeightForWidth(true);
    QLabel::setSizePolicy(policy);
    QLabel::setScaledContents(true);
}

void ImageLabel::setPixmap ( const QPixmap &pixmap ){
    this->size = pixmap.size();
    QLabel::setPixmap(pixmap);
}

int main(int argc, char *argv[]){
    QApplication a(argc, argv);

    QFrame *frame = new QFrame;
    QVBoxLayout *layout = new QVBoxLayout;
    frame->setLayout(layout);

    QPixmap map;
    map.load("test.png");
    ImageLabel *label = new ImageLabel;
    label->setSizePolicy();
    label->setPixmap(map);
    layout->addWidget(label);
    frame->show();

    return a.exec();
}

推薦答案

有幾種方法可以做到這一點(diǎn)，但最重要的是，我建議不要通過嘗試暗示方面來對抗布局系統(tǒng).如您所見，您必須嘗試實(shí)現(xiàn)一些方法來幫助布局.

There are a couple ways to do this, but most of all I would recommend maybe not fighting against the layout system by trying to hint the aspect. As you can see, you are having to try and implement a number methods trying to help the layout.

我可以舉兩個(gè)例子.他們都不使用布局...

I can offer two examples. Neither of them use layouts...

第一個(gè)使用子 QLabel 來顯示圖像，并通過調(diào)整大小事件驅(qū)動其固定大小:

The first uses a child QLabel to show the image, and drives its fixed size off of the resize event:

// imagelabel.h

class ImageLabel : public QWidget
{
    Q_OBJECT

public:
    explicit ImageLabel(QWidget *parent = 0);
    const QPixmap* pixmap() const;

public slots:
    void setPixmap(const QPixmap&);

protected:
    void resizeEvent(QResizeEvent *);

private slots:
    void resizeImage();

private:
    QLabel *label;
};

// imagelabel.cpp

ImageLabel::ImageLabel(QWidget *parent) :
    QWidget(parent)
{
    label = new QLabel(this);
    label->setScaledContents(true);
    label->setFixedSize(0,0);
}

void ImageLabel::resizeEvent(QResizeEvent *event) {
    QWidget::resizeEvent(event);
    resizeImage();
}

const QPixmap* ImageLabel::pixmap() const {
    return label->pixmap();
}

void ImageLabel::setPixmap (const QPixmap &pixmap){
    label->setPixmap(pixmap);
    resizeImage();
}

void ImageLabel::resizeImage() {
    QSize pixSize = label->pixmap()->size();
    pixSize.scale(size(), Qt::KeepAspectRatio);
    label->setFixedSize(pixSize);
}

第二個(gè)示例基于@Arnold_Spence 給出的答案.它甚至更短，因?yàn)樗皇褂米?QLabel.它只是在繪制事件中繪制像素圖:

The second example is based off of the answer given by @Arnold_Spence. It is even shorter as it doesn't use a child QLabel. It just draws the pixmap in the paint event:

// imagelabel2.h

class ImageLabel2 : public QWidget
{
    Q_OBJECT

public:
    explicit ImageLabel2(QWidget *parent = 0);
    const QPixmap* pixmap() const;

public slots:
    void setPixmap(const QPixmap&);

protected:
    void paintEvent(QPaintEvent *);

private:
    QPixmap pix;
};

// imagelabel2.cpp

ImageLabel2::ImageLabel2(QWidget *parent) :
    QWidget(parent)
{
}

void ImageLabel2::paintEvent(QPaintEvent *event) {
    QWidget::paintEvent(event);

    if (pix.isNull())
        return;

    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);

    QSize pixSize = pix.size();
    pixSize.scale(event->rect().size(), Qt::KeepAspectRatio);

    QPixmap scaledPix = pix.scaled(pixSize,
                                   Qt::KeepAspectRatio,
                                   Qt::SmoothTransformation
                                   );

    painter.drawPixmap(QPoint(), scaledPix);

}

const QPixmap* ImageLabel2::pixmap() const {
    return &pix;
}

void ImageLabel2::setPixmap (const QPixmap &pixmap){
    pix = pixmap;
}

這篇關(guān)于如何使圖像調(diào)整大小以在 Qt 中縮放?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！