Qt窗口拖動及改變大小

#ifndef MYDRAGQT_H
#define MYDRAGQT_H

#include <QtWidgets/QWidget>
#include "ui_mydragqt.h"

class MyDragQt : public QWidget
{
    Q_OBJECT

public:
    MyDragQt(QWidget *parent = 0);
    ~MyDragQt();

private:
    Ui::MyDragQtClass ui;
private:
    void paintEvent(QPaintEvent*);
    void mousePressEvent (QMouseEvent* event);
    void mouseReleaseEvent(QMouseEvent* event);
    void mouseMoveEvent(QMouseEvent* event);
private:
    //輔助函數
    int calcPosition(const QPoint& pt);
    void setCursorType(int value);
private:
    bool                    m_bLeftMouseButtonPressed;
    int                     m_lastPosition;
    QPoint                  m_ptLast;
    Qt::CursorShape         m_currentCursor;
};

#endif // MYDRAGQT_H

實現：

#include "mydragqt.h"

#include <QPainter>
#include <QMouseEvent>
#include <QDebug>
namespace
{
    const int g_padding = 4;

    int helperCalcPosition(int pos, int range)
    {
        return (pos < g_padding) ? 0 : ((pos > (range - g_padding)) ? 2 : 1);
    }
}


MyDragQt::MyDragQt(QWidget *parent)
    : QWidget(parent, Qt::FramelessWindowHint)
    , m_bLeftMouseButtonPressed(false)
    , m_lastPosition(11)
    , m_currentCursor(Qt::ArrowCursor)
{
    ui.setupUi(this);
    setMouseTracking(true);
    setCursor(m_currentCursor);

    this->setMinimumSize(QSize(280, 360));
}

MyDragQt::~MyDragQt()
{

}

void MyDragQt::paintEvent(QPaintEvent*)
{
    QPainter p(this);
    p.fillRect(rect(), Qt::black);
}

int MyDragQt::calcPosition(const QPoint& pt)
{
    int row = helperCalcPosition(pt.y(), rect().height());
    int col = helperCalcPosition(pt.x(), rect().width());
    return row * 10 + col;
}

void MyDragQt::mousePressEvent(QMouseEvent* event)
{
    m_bLeftMouseButtonPressed = true;
    m_ptLast = event->globalPos();
    m_lastPosition = calcPosition(event->pos());
    event->ignore();
}

void MyDragQt::mouseReleaseEvent(QMouseEvent* event)
{
    if(m_bLeftMouseButtonPressed) m_bLeftMouseButtonPressed = false;
    event->ignore();
}

void MyDragQt::mouseMoveEvent(QMouseEvent* event)
{
    setCursorType(calcPosition(event->pos()));
    if(m_bLeftMouseButtonPressed)
    {
        QPoint ptNew = event->globalPos();
        ptNew -= m_ptLast;
        if(11 == m_lastPosition) //拖動
        {
            ptNew += pos();
            move(ptNew);
        }
        else //調整大小
        {
            QRect rectWindow = geometry();
            switch(m_lastPosition)
            {
            case 00:
                rectWindow.setTopLeft(rectWindow.topLeft() + ptNew);
                break;
            case 02:
                rectWindow.setTopRight(rectWindow.topRight() + ptNew);
                break;
            case 20:
                rectWindow.setBottomLeft(rectWindow.bottomLeft() + ptNew);
                break;
            case 22:
                rectWindow.setBottomRight(rectWindow.bottomRight() + ptNew);
                break;
            case 10:
                rectWindow.setLeft(rectWindow.left() + ptNew.x());
                break;
            case 12:
                rectWindow.setRight(rectWindow.right() + ptNew.x());
                break;
            case 01:
                rectWindow.setTop(rectWindow.top() + ptNew.y());
                break;
            case 21:
                rectWindow.setBottom(rectWindow.bottom() + ptNew.y());
                break;
            //case 11:
            default:
                Q_ASSERT(0);
            }
            setGeometry(rectWindow);
            //qDebug() << rectWindow.topLeft() << ", " << rectWindow.bottomRight();
        }
        m_ptLast  = event->globalPos();
    }
    event->ignore();
}

void MyDragQt::setCursorType(int value)
{
    Qt::CursorShape cursor;

    switch(value)
    {
    case 00:
    case 22:
        cursor = Qt::SizeFDiagCursor;
        break;
    case 02:
    case 20:
        cursor = Qt::SizeBDiagCursor;
        break;
    case 10:
    case 12:
        cursor = Qt::SizeHorCursor;
        break;
    case 01:
    case 21:
        cursor = Qt::SizeVerCursor;
        break;
    case 11:
        cursor = Qt::ArrowCursor;
        break;
    default:
        Q_ASSERT(0);
        break;
    }
    if(cursor != m_currentCursor)
    {
        m_currentCursor = cursor;
        setCursor(m_currentCursor);
    }
}

這個實現比大多數的要精簡。下一步繼續優化，爭取再減少一個成員變量。