Qt之邊界佈局（BorderLayout）

簡述

顧名思義，BorderLayout可以以一種子控件圍繞某個中心區域的方式來對控件進行佈局。

邊界佈局是一種自定義佈局，BorderLayout不是Qt自帶的標準類，而是以源碼的形式提供的。

使用

下面先介紹BorderLayout類的使用以及效果，後面給出實現細節

效果

源碼

    QTextBrowser *centralWidget = new QTextBrowser;
    centralWidget->setPlainText(tr("Central widget"));

    BorderLayout *layout = new BorderLayout;
    layout->addWidget(centralWidget, BorderLayout::Center);
    layout->addWidget(createLabel("North"), BorderLayout::North);
    layout->addWidget(createLabel("West"), BorderLayout::West);
    layout->addWidget(createLabel("East 1"), BorderLayout::East);
    layout->addWidget(createLabel("East 2") , BorderLayout::East);
    layout->addWidget(createLabel("South"), BorderLayout::South);
    setLayout(layout);

    setWindowTitle(tr("Border Layout"));

QLabel *Widget::createLabel(const QString &text)
{
    QLabel *label = new QLabel(text);
    label->setFrameStyle(QFrame::Box | QFrame::Raised);
    return label;
}

BorderLayout實現

borderlayout.h

#ifndef BORDERLAYOUT_H
#define BORDERLAYOUT_H

#include <QLayout>
#include <QRect>

class BorderLayout : public QLayout
{
public:
    enum Position { West, North, South, East, Center };

    explicit BorderLayout(QWidget *parent, int margin = 0, int spacing = -1);
    BorderLayout(int spacing = -1);
    ~BorderLayout();

    void addItem(QLayoutItem *item) override;
    void addWidget(QWidget *widget, Position position);
    Qt::Orientations expandingDirections() const override;
    bool hasHeightForWidth() const override;
    int count() const override;
    QLayoutItem *itemAt(int index) const override;
    QSize minimumSize() const override;
    void setGeometry(const QRect &rect) override;
    QSize sizeHint() const override;
    QLayoutItem *takeAt(int index) override;

    void add(QLayoutItem *item, Position position);

private:
    struct ItemWrapper
    {
        ItemWrapper(QLayoutItem *i, Position p) {
            item = i;
            position = p;
        }

        QLayoutItem *item;
        Position position;
    };

    enum SizeType { MinimumSize, SizeHint };
    QSize calculateSize(SizeType sizeType) const;

    QList<ItemWrapper *> list;
};

#endif // BORDERLAYOUT_H

borderlayout.c

#include "borderlayout.h"

BorderLayout::BorderLayout(QWidget *parent, int margin, int spacing)
    : QLayout(parent)
{
    setMargin(margin);
    setSpacing(spacing);
}

BorderLayout::BorderLayout(int spacing)
{
    setSpacing(spacing);
}

BorderLayout::~BorderLayout()
{
    QLayoutItem *l;
    while ((l = takeAt(0)))
        delete l;
}

void BorderLayout::addItem(QLayoutItem *item)
{
    add(item, West);
}

void BorderLayout::addWidget(QWidget *widget, Position position)
{
    add(new QWidgetItem(widget), position);
}

Qt::Orientations BorderLayout::expandingDirections() const
{
    return Qt::Horizontal | Qt::Vertical;
}

bool BorderLayout::hasHeightForWidth() const
{
    return false;
}

int BorderLayout::count() const
{
    return list.size();
}

QLayoutItem *BorderLayout::itemAt(int index) const
{
    ItemWrapper *wrapper = list.value(index);
    if (wrapper)
        return wrapper->item;
    else
        return 0;
}

QSize BorderLayout::minimumSize() const
{
    return calculateSize(MinimumSize);
}

void BorderLayout::setGeometry(const QRect &rect)
{
    ItemWrapper *center = 0;
    int eastWidth = 0;
    int westWidth = 0;
    int northHeight = 0;
    int southHeight = 0;
    int centerHeight = 0;
    int i;

    QLayout::setGeometry(rect);

    for (i = 0; i < list.size(); ++i) {
        ItemWrapper *wrapper = list.at(i);
        QLayoutItem *item = wrapper->item;
        Position position = wrapper->position;

        if (position == North) {
            item->setGeometry(QRect(rect.x(), northHeight, rect.width(),
                                    item->sizeHint().height()));

            northHeight += item->geometry().height() + spacing();
        } else if (position == South) {
            item->setGeometry(QRect(item->geometry().x(),
                                    item->geometry().y(), rect.width(),
                                    item->sizeHint().height()));

            southHeight += item->geometry().height() + spacing();

            item->setGeometry(QRect(rect.x(),
                              rect.y() + rect.height() - southHeight + spacing(),
                              item->geometry().width(),
                              item->geometry().height()));
        } else if (position == Center) {
            center = wrapper;
        }
    }

    centerHeight = rect.height() - northHeight - southHeight;

    for (i = 0; i < list.size(); ++i) {
        ItemWrapper *wrapper = list.at(i);
        QLayoutItem *item = wrapper->item;
        Position position = wrapper->position;

        if (position == West) {
            item->setGeometry(QRect(rect.x() + westWidth, northHeight,
                                    item->sizeHint().width(), centerHeight));

            westWidth += item->geometry().width() + spacing();
        } else if (position == East) {
            item->setGeometry(QRect(item->geometry().x(), item->geometry().y(),
                                    item->sizeHint().width(), centerHeight));

            eastWidth += item->geometry().width() + spacing();

            item->setGeometry(QRect(
                              rect.x() + rect.width() - eastWidth + spacing(),
                              northHeight, item->geometry().width(),
                              item->geometry().height()));
        }
    }

    if (center)
        center->item->setGeometry(QRect(westWidth, northHeight,
                                        rect.width() - eastWidth - westWidth,
                                        centerHeight));
}

QSize BorderLayout::sizeHint() const
{
    return calculateSize(SizeHint);
}

QLayoutItem *BorderLayout::takeAt(int index)
{
    if (index >= 0 && index < list.size()) {
        ItemWrapper *layoutStruct = list.takeAt(index);
        return layoutStruct->item;
    }
    return 0;
}

void BorderLayout::add(QLayoutItem *item, Position position)
{
    list.append(new ItemWrapper(item, position));
}

QSize BorderLayout::calculateSize(SizeType sizeType) const
{
    QSize totalSize;

    for (int i = 0; i < list.size(); ++i) {
        ItemWrapper *wrapper = list.at(i);
        Position position = wrapper->position;
        QSize itemSize;

        if (sizeType == MinimumSize)
            itemSize = wrapper->item->minimumSize();
        else // (sizeType == SizeHint)
            itemSize = wrapper->item->sizeHint();

        if (position == North || position == South || position == Center)
            totalSize.rheight() += itemSize.height();

        if (position == West || position == East || position == Center)
            totalSize.rwidth() += itemSize.width();
    }
    return totalSize;
}

引用

---

[1] Qt助手

[2] https://blog.csdn.net/liang19890820/article/details/51519088