技術標籤：Qt案例

文章目錄

• main.cpp
• Window.h
• Window.cpp
• FlowLayout.h
• FlowLayout.cpp

Flow Layout Example

演示如何為不同的視窗大小排列小部件。

Flow Layout實現處理不同視窗大小的佈局。小部件的位置根據應用程式視窗的寬度而變化。

Flowlayout類主要使用QLayout和QWidgetItem，而視窗使用QWidget和QLabel。

有關詳細資訊，請訪問佈局管理頁面。

main.cpp

#include <QApplication>
#include "window.h"
 


int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    Window window;
    window.show();
    return app.exec();
}

Window.h

#ifndef WINDOW_H
#define WINDOW_H

#include <QWidget>

QT_BEGIN_NAMESPACE
class QLabel;
QT_END_NAMESPACE

class Window : public QWidget
{
    Q_OBJECT

public
 
:
    Window();
};
#endif // WINDOW_H

Window.cpp

#include <QPushButton>

#include "flowlayout.h"
#include "window.h"

Window::Window()
{
    FlowLayout *flowLayout = new FlowLayout;

    flowLayout->addWidget(new QPushButton(tr("Short")));
    flowLayout->addWidget
 
(new QPushButton(tr("Longer")));
    flowLayout->addWidget(new QPushButton(tr("Different text")));
    flowLayout->addWidget(new QPushButton(tr("More text")));
    flowLayout->addWidget(new QPushButton(tr("Even longer button text")));
    setLayout(flowLayout);

    setWindowTitle(tr("Flow Layout"));
}

FlowLayout.h

FlowLayout類繼承QLayout。它是一個自定義佈局類，水平和垂直排列其子視窗小部件。

我們重新實現從QLayout繼承的函式。這些函式將項新增到佈局中，並處理它們的方向和幾何圖形。
我們還聲明瞭兩個私有方法，doLayout() 和smartSpacing() 。doLayout() 列出佈局項，而smartSpacing() 函式計算它們之間的間距。

#ifndef FLOWLAYOUT_H
#define FLOWLAYOUT_H

#include <QLayout>
#include <QRect>
#include <QStyle>

class FlowLayout : public QLayout
{
public:
    explicit FlowLayout(QWidget *parent, int margin = -1, int hSpacing = -1, int vSpacing = -1);
    explicit FlowLayout(int margin = -1, int hSpacing = -1, int vSpacing = -1);
    ~FlowLayout();

    void addItem(QLayoutItem *item) override;
    int horizontalSpacing() const;
    int verticalSpacing() const;
    Qt::Orientations expandingDirections() const override;
    bool hasHeightForWidth() const override;
    int heightForWidth(int) 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;

private:
    int doLayout(const QRect &rect, bool testOnly) const;
    int smartSpacing(QStyle::PixelMetric pm) const;

    QList<QLayoutItem *> itemList;
    int m_hSpace;
    int m_vSpace;
};
#endif // FLOWLAYOUT_H

FlowLayout.cpp

#include <QtWidgets>
#include "flowlayout.h"

/*在建構函式中，我們呼叫setContentsMargins() 來設定左、上、右和下邊距。
 * 預設情況下，QLayout使用當前樣式提供的值（請參見QStyle:：PixelMetric）。*/
FlowLayout::FlowLayout(QWidget *parent, int margin, int hSpacing, int vSpacing)
    : QLayout(parent), m_hSpace(hSpacing), m_vSpace(vSpacing)
{
    setContentsMargins(margin, margin, margin, margin);
}
// 建構函式過載
FlowLayout::FlowLayout(int margin, int hSpacing, int vSpacing)
    : m_hSpace(hSpacing), m_vSpace(vSpacing)
{
    setContentsMargins(margin, margin, margin, margin);
}
/* 解構函式 */
FlowLayout::~FlowLayout()
{
    QLayoutItem *item;
    while ((item = takeAt(0)))
        delete item;
}

/* 增加專案 */
void FlowLayout::addItem(QLayoutItem *item)
{
    itemList.append(item);
}

/* 返回水平間隔*/
int FlowLayout::horizontalSpacing() const
{
    if (m_hSpace >= 0) {
        return m_hSpace;
    } else {
        return smartSpacing(QStyle::PM_LayoutHorizontalSpacing);
    }
}
/* 返回垂直間隔*/
int FlowLayout::verticalSpacing() const
{
    if (m_vSpace >= 0) {
        return m_vSpace;
    } else {
        return smartSpacing(QStyle::PM_LayoutVerticalSpacing);
    }
}

/* 返回佈局專案的數量 */
int FlowLayout::count() const
{
    return itemList.size();
}
/* 索引布局專案 */
QLayoutItem *FlowLayout::itemAt(int index) const
{
    return itemList.value(index);
}
/* 移除索引的佈局專案 */
QLayoutItem *FlowLayout::takeAt(int index)
{
    if (index >= 0 && index < itemList.size())
        return itemList.takeAt(index);
    return nullptr;
}

//Qt::Orientations FlowLayout::expandingDirections() const
//{
//    return { };
//}

/*首選高度是否取決於其寬度*/
bool FlowLayout::hasHeightForWidth() const
{
    return true;
}
/*返回此佈局項的首選高度（給定寬度）*/
int FlowLayout::heightForWidth(int width) const
{
    int height = doLayout(QRect(0, 0, width, 0), true);
    return height;
}

/* 設定幾何體 */
void FlowLayout::setGeometry(const QRect &rect)
{
    QLayout::setGeometry(rect);
    doLayout(rect, false);
}
/* 返回大小提示 */
QSize FlowLayout::sizeHint() const
{
    return minimumSize();
}
/* 返回最小的尺寸 */
QSize FlowLayout::minimumSize() const
{
    QSize size;
    for (const QLayoutItem *item : qAsConst(itemList))
        size = size.expandedTo(item->minimumSize());

    const QMargins margins = contentsMargins();
    size += QSize(margins.left() + margins.right(), margins.top() + margins.bottom());
    return size;
}

/* 進行佈局 */
int FlowLayout::doLayout(const QRect &rect, bool testOnly) const
{
    int left, top, right, bottom;
    getContentsMargins(&left, &top, &right, &bottom);
    QRect effectiveRect = rect.adjusted(+left, +top, -right, -bottom);
    int x = effectiveRect.x();
    int y = effectiveRect.y();
    int lineHeight = 0;

    for (QLayoutItem *item : qAsConst(itemList)) {
        const QWidget *wid = item->widget();
        int spaceX = horizontalSpacing();
        if (spaceX == -1)
            spaceX = wid->style()->layoutSpacing(
                        QSizePolicy::PushButton, QSizePolicy::PushButton, Qt::Horizontal);
        int spaceY = verticalSpacing();
        if (spaceY == -1)
            spaceY = wid->style()->layoutSpacing(
                        QSizePolicy::PushButton, QSizePolicy::PushButton, Qt::Vertical);


        int nextX = x + item->sizeHint().width() + spaceX;
        if (nextX - spaceX > effectiveRect.right() && lineHeight > 0) {
            x = effectiveRect.x();
            y = y + lineHeight + spaceY;
            nextX = x + item->sizeHint().width() + spaceX;
            lineHeight = 0;
        }

        if (!testOnly)
            item->setGeometry(QRect(QPoint(x, y), item->sizeHint()));

        x = nextX;
        lineHeight = qMax(lineHeight, item->sizeHint().height());
    }
    return y + lineHeight - rect.y() + bottom;
}

// 智慧空間區域
int FlowLayout::smartSpacing(QStyle::PixelMetric pm) const
{
    QObject *parent = this->parent();
    if (!parent) {
        return -1;
    } else if (parent->isWidgetType()) {   // parent是QWidget
        QWidget *pw = static_cast<QWidget *>(parent);
        return pw->style()->pixelMetric(pm, nullptr, pw);
    } else {
        return static_cast<QLayout *>(parent)->spacing();
    }
}