在调整大小时保持子类QWidget的宽高比 [英] Keeping the aspect ratio of a sub-classed QWidget during resize

问题描述

我正在创建一个新的小部件，通过继承QWidget类。我想为这个小部件设置一个比例（对于它的高度和宽度），并且总是保持不变。

I'm creating a new widget, by subclassing the QWidget class. I'd like to be able to set a ratio (for its height and its width) for this widget, which will always be maintained.

为此，总是搜索，使用Qt5文档，Google和Stackoverflow。显然，我找到了答案：特别是这一个。但是，不幸的是，甚至没有一个完全有效：

For this, I've always searched, using the Qt5 documentation, Google, and Stackoverflow. Obviously, I've found answers: in particular, this one. But, unfortunately, not even one is fully effective:

• 设置 sizeIncrement 即使窗口小部件是一个窗口


• 我试图重载resizeEvent，但我真的不知道该怎么做...



• 如果我遵循此答案，有两件事：

• Setting the sizeIncrement does totally nothing, even if the widget is a window
• I tried to overload resizeEvent, but I really don't know how to do this...

• If I follow this answer, two things:

1. 如果窗口小部件是顶级窗口，则比率不会维持，我可以根据需要调整大小。


2. 如果我将此窗口小部件放置在布局中，如果我只是增加窗口的宽度和高度，则保持比率。但是，一旦我增加宽度或高度到很多，小部件是扁平。相反，我希望布局自动调整其大小以保持小部件的比率。

那么，我如何能够保持子类QWidget的宽高比？

So, how could I manage to keep the aspect ratio of a subclassed QWidget?

推荐答案

， AspectRatioWidget ），在其中放置您的小部件。对于父窗口部件，子类QWidget并给它一个QBoxLayout。把你的小部件放在中心，并在任一侧的QSpacerItems。然后在父窗口小部件的 QWidget :: resizeEvent 中根据需要调整方向和伸展。我提供了一个例子如下。要使用，只需创建 AspectRatioWidget 的实例，并传递构造函数指向您的小部件和所需的宽高比。

Create a parent widget (e.g., AspectRatioWidget) in which to place your widget. For the parent widget, subclass QWidget and give it a QBoxLayout. Put your widget into the center, and QSpacerItems on either side. Then in the parent widget's QWidget::resizeEvent adjust the direction and stretches as needed. I've provided an example below. To use, just create an instance of AspectRatioWidget and pass the constructor a pointer to your widget and the desired aspect ratio.

// header
class AspectRatioWidget : public QWidget
{
public:
    AspectRatioWidget(QWidget *widget, float width, float height, QWidget *parent = 0);
    void resizeEvent(QResizeEvent *event);

private:
    QBoxLayout *layout;
    float arWidth; // aspect ratio width
    float arHeight; // aspect ratio height
};

// cpp
AspectRatioWidget::AspectRatioWidget(QWidget *widget, float width, float height, QWidget *parent) :
    QWidget(parent), arWidth(width), arHeight(height)
{
    layout = new QBoxLayout(QBoxLayout::LeftToRight, this);

    // add spacer, then your widget, then spacer
    layout->addItem(new QSpacerItem(0, 0));
    layout->addWidget(widget);
    layout->addItem(new QSpacerItem(0, 0));
}

void AspectRatioWidget::resizeEvent(QResizeEvent *event)
{
    float thisAspectRatio = (float)event->size().width() / event->size().height();
    int widgetStretch, outerStretch;

    if (thisAspectRatio > (arWidth/arHeight)) // too wide
    {
        layout->setDirection(QBoxLayout::LeftToRight);
        widgetStretch = height() * (arWidth/arHeight); // i.e., my width
        outerStretch = (width() - widgetStretch) / 2 + 0.5;
    }
    else // too tall
    {
        layout->setDirection(QBoxLayout::TopToBottom);
        widgetStretch = width() * (arHeight/arHeight); // i.e., my height
        outerStretch = (height() - widgetStretch) / 2 + 0.5;
    }

    layout->setStretch(0, outerStretch);
    layout->setStretch(1, widgetStretch);
    layout->setStretch(2, outerStretch);
}

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