QT实现鼠标拖动调整窗口大小

要想实现该功能，我们需要考虑一下几个问题。

1、如何获取鼠标的移动，点击，释放

    通过实现一下几个事件来获取窗体的事件

    void mouseMoveEvent(QMouseEvent *event);

    void mousePressEvent(QMouseEvent *event);

    void mouseReleaseEvent(QMouseEvent *event);

2、如何判断鼠标是否移动到窗体的边界

    一个窗体的结构大概如下图所示

    上左   上   上右

    左       中     右   

    下左   下    下右

    那么我们用数字来表示如下

    11    12    13

    21    22    23

    31    32    33

    那么我们就得到鼠标在除了22的位置就到达了窗体的边界

上代码：

enum {
    TOPLEFT = 11,
    TOP = 12,
    TOPRIGHT = 13,
    LEFT = 21,
    CENTER = 22,
    RIGHT = 23,
    BUTTOMLEFT = 31,
    BUTTOM = 32,
    BUTTOMRIGHT = 33
};

#define FRAMESHAPE 10    

public:
    void mouseMoveEvent(QMouseEvent *event);
    void mousePressEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);
    int CalCursorCol(QPoint pt);    //计算鼠标X的位置 
    int CalCursorPos(QPoint pt, int colPos);    //计算鼠标的位置
    void setCursorShape(int CalPos);    //设置鼠标对应位置的形状

private:
    int     m_iCalCursorPos;
    bool    m_bLeftPress;
    QRect   m_rtPreGeometry;
    QPoint  m_ptViewMousePos;

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget),
    m_bLeftPress(false)
{
    ui->setupUi(this);
    this->setWindowFlags(Qt::FramelessWindowHint);    //取消窗体的标题栏
    setMouseTracking(true);   //MouseMoveEvent为了不太耗资源在默认状态下是要鼠标按下才能捕捉到，要想鼠标不按下时的移动也能捕捉到设置为true
}

Widget::~Widget()
{
    delete ui;
}

void Widget::mouseMoveEvent(QMouseEvent *event)
{
    //窗体不是最大的话就改变鼠标的形状
    if(Qt::WindowMaximized != windowState())
    {
        setCursorShape(CalCursorPos(event->pos(),CalCursorCol(event->pos())));
    }
    //获取当前的点，这个点是全局的
    QPoint ptCurrentPos = QCursor::pos();
    //计算出移动的位置，当前点 - 鼠标左键按下的点
    QPoint ptMoveSize = ptCurrentPos - m_ptViewMousePos;
    QRect rtTempGeometry = m_rtPreGeometry;
    if(m_bLeftPress)
    {
        switch(m_iCalCursorPos)
        {
        case TOPLEFT:
            rtTempGeometry.setTopLeft(m_rtPreGeometry.topLeft()+ptMoveSize);
            break;
        case TOP:
            rtTempGeometry.setTop(m_rtPreGeometry.top()+ptMoveSize.y());
            break;
        case TOPRIGHT:
            rtTempGeometry.setTopRight(m_rtPreGeometry.topRight()+ptMoveSize);
            break;
        case LEFT:
            rtTempGeometry.setLeft(m_rtPreGeometry.left()+ptMoveSize.x());
            break;
        case RIGHT:
            rtTempGeometry.setRight(m_rtPreGeometry.right()+ptMoveSize.x());
            break;
        case BUTTOMLEFT:
            rtTempGeometry.setBottomLeft(m_rtPreGeometry.bottomLeft()+ptMoveSize);
            break;
        case BUTTOM:
            rtTempGeometry.setBottom(m_rtPreGeometry.bottom()+ptMoveSize.y());
            break;
        case BUTTOMRIGHT:
            rtTempGeometry.setBottomRight(m_rtPreGeometry.bottomRight()+ptMoveSize);
            break;
        default:
            break;
        }
        //移动窗体，如果比最小窗体大，就移动
        if(rtTempGeometry.width() >= 200 && rtTempGeometry.height() >= 300)
            setGeometry(rtTempGeometry);

    }
}

void Widget::mousePressEvent(QMouseEvent *event)
{
    m_iCalCursorPos = CalCursorPos(event->pos(),CalCursorCol(event->pos()));
    if (event->button() == Qt::LeftButton /*&& Qt::WindowMaximized != windowState()*/)
    {
        if(m_iCalCursorPos != CENTER)
        {
            m_bLeftPress = true;
        }
    }
    m_rtPreGeometry = geometry();
    m_ptViewMousePos = event->globalPos();
}

void Widget::mouseReleaseEvent(QMouseEvent *event)
{
    m_bLeftPress = false;
    QApplication::restoreOverrideCursor();
}

int Widget::CalCursorCol(QPoint pt)
{
    return (pt.x() < FRAMESHAPE ? 1 : ((pt.x() > this->width() - FRAMESHAPE) ? 3 : 2));
}

int Widget::CalCursorPos(QPoint pt, int colPos)
{
    return ((pt.y() < FRAMESHAPE ? 10 : ((pt.y() > this->height() - FRAMESHAPE) ? 30 : 20)) + colPos);
}

void Widget::setCursorShape(int CalPos)
{
    Qt::CursorShape cursor;
    switch(CalPos)
    {
    case TOPLEFT:
    case BUTTOMRIGHT:
        cursor = Qt::SizeFDiagCursor;
        break;
    case TOPRIGHT:
    case BUTTOMLEFT:
        cursor = Qt::SizeBDiagCursor;
        break;
    case TOP:
    case BUTTOM:
        cursor = Qt::SizeVerCursor;
        break;
    case LEFT:
    case RIGHT:
        cursor = Qt::SizeHorCursor;
        break;
    default:
        cursor = Qt::ArrowCursor;
        break;
    }
    setCursor(cursor);
}