Qt隐藏系统的窗口框架后如何移动窗口，如何改变其大小？

做项目时，为了界面美观些，把系统提供的窗口框架去掉后（无框架窗口），最令人恶心的是，无法改变无边框窗口的大小，也无法移动窗口。

1、首先要了解一下九宫格，什么是九宫格？

一个窗体可以被划分为上、下、左、右、左上、左下、右上、右下、中间。除了中间部分，其余都要写代码。

设外边框（如左部分）的宽度都为 Padding；

2、在头文件中我们加一个宏定义，及一个用于判断鼠标将要移动方向的枚举：

#define PADDING 1
enum Direction   //拖动方向
{
    UP=0,
    DOWN=1,
    LEFT,
    RIGHT,
    LEFTTOP,
    LEFTBOTTOM,
    RIGHTBOTTOM,
    RIGHTTOP,
    NONE
};

3、在头文件中声明：

public:
    void region(const QPoint &currentGlobalPoint);  //鼠标的位置,改变光标
protected:
    //鼠标按下移动及释放事件
    void mousePressEvent(QMouseEvent *event);  
    void mouseMoveEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);

private:
    QPoint m_movePoint;  //鼠标的位置
    bool isLeftPressDown;  // 判断左键是否按下
    Direction dir;        // 窗口大小改变时，记录改变方向

4、在构造函数中做初始化：

    this->setMinimumHeight(100);
    this->setMinimumWidth(150);
    this->setWindowFlags(Qt::FramelessWindowHint); // 设置成无边框对话框

    this->isLeftPressDown = false;
    this->dir= NONE;

    this->setMouseTracking(true);   // 追踪鼠标（没有鼠标键被按下也可以追踪鼠标的位置）

5、定义一个方法 void region(const QPoint &currentGlobalPoint);
用于判断鼠标位置，并且改变光标形状。

void MusicWidget::region(const QPoint &currentGlobalPoint)
{
    // 获取窗体在屏幕上的位置区域，topLeft为坐上角点，rightButton为右下角点
    QRect rect = this->rect();

    QPoint topLeft = this->mapToGlobal(rect.topLeft()); //将左上角的(0,0)转化为全局坐标
    QPoint rightButton = this->mapToGlobal(rect.bottomRight());

    int x = currentGlobalPoint.x(); //当前鼠标的坐标
    int y = currentGlobalPoint.y();

    if(((topLeft.x() + PADDING >= x) && (topLeft.x() <= x))
            && ((topLeft.y() + PADDING >= y) && (topLeft.y() <= y)))
    {
        // 左上角
        dir = LEFTTOP;
        this->setCursor(QCursor(Qt::SizeFDiagCursor));  // 设置光标形状
    }else if(((x >= rightButton.x() - PADDING) && (x <= rightButton.x()))
              && ((y >= rightButton.y() - PADDING) && (y <= rightButton.y())))
    {
        // 右下角
        dir = RIGHTBOTTOM;
        this->setCursor(QCursor(Qt::SizeFDiagCursor));
    }else if(((x <= topLeft.x() + PADDING) && (x >= topLeft.x()))
              && ((y >= rightButton.y() - PADDING) && (y <= rightButton.y())))
    {
        //左下角
        dir = LEFTBOTTOM;
        this->setCursor(QCursor(Qt::SizeBDiagCursor));
    }else if(((x <= rightButton.x()) && (x >= rightButton.x() - PADDING))
              && ((y >= topLeft.y()) && (y <= topLeft.y() + PADDING)))
    {
        // 右上角
        dir = RIGHTTOP;
        this->setCursor(QCursor(Qt::SizeBDiagCursor));
    }else if((x <= topLeft.x() + PADDING) && (x >= topLeft.x()))
    {
        // 左边
        dir = LEFT;
        this->setCursor(QCursor(Qt::SizeHorCursor));
    }else if((x <= rightButton.x()) && (x >= rightButton.x() - PADDING))
    {
        // 右边
        dir = RIGHT;
        this->setCursor(QCursor(Qt::SizeHorCursor));
    }else if((y >= topLeft.y()) && (y <= topLeft.y() + PADDING))
    {
        // 上边
        dir = UP;
        this->setCursor(QCursor(Qt::SizeVerCursor));
    }else if((y <= rightButton.y()) && (y >= rightButton.y() - PADDING))
    {
        // 下边
        dir = DOWN;
        this->setCursor(QCursor(Qt::SizeVerCursor));
    }else
    {
        // 默认
        dir = NONE;
        this->setCursor(QCursor(Qt::ArrowCursor));
    }
}

6、接下来对三个鼠标事件进行重载：

mousePressEvent

//鼠标按下事件
void MusicWidget::mousePressEvent(QMouseEvent *event)
{
    switch(event->button())
    {
        case Qt::LeftButton:
            isLeftPressDown = true;

            if(dir != NONE)
            {
                this->mouseGrabber(); //返回当前抓取鼠标输入的窗口
            }
            else
            {
                m_movePoint = event->globalPos() - this->frameGeometry().topLeft();
                //globalPos()鼠标位置，topLeft()窗口左上角的位置
            }
            break;
        case Qt::RightButton:
            this->setWindowState(Qt::WindowMinimized);
            break;
        default:
            MusicWidget::mousePressEvent(event);
    }
}

mouseMoveEvent

//鼠标移动事件
void MusicWidget::mouseMoveEvent(QMouseEvent *event)
{
    QPoint globalPoint = event->globalPos(); //鼠标全局坐标

    QRect rect = this->rect(); //rect == QRect(0,0 680x412)
    QPoint topLeft = mapToGlobal(rect.topLeft());
    QPoint bottomRight = mapToGlobal(rect.bottomRight());

    if (this->windowState() != Qt::WindowMaximized)
    {
        if(!isLeftPressDown)  //没有按下左键时
        {
            this->region(globalPoint); //窗口大小的改变——判断鼠标位置，改变光标形状
        }
        else
        {
            if(dir != NONE)
            {
                QRect newRect(topLeft, bottomRight); //定义一个矩形

                switch(dir)
                {
                    case LEFT:

                        if(bottomRight.x() - globalPoint.x() <= this->minimumWidth())
                        {
                            newRect.setLeft(topLeft.x()); //小于界面的最小宽度时，设置为左上角横坐标为窗口x
                            //只改变左边界
                        }
                        else
                        {
                            newRect.setLeft(globalPoint.x());
                        }
                        break;
                    case RIGHT:
                        newRect.setWidth(globalPoint.x() - topLeft.x()); //只能改变右边界
                        break;
                    case UP:
                        if(bottomRight.y() - globalPoint.y() <= this->minimumHeight())
                        {
                            newRect.setY(topLeft.y());
                        }
                        else
                        {
                            newRect.setY(globalPoint.y());
                        }
                        break;
                    case DOWN:
                        newRect.setHeight(globalPoint.y() - topLeft.y());
                        break;
                    case LEFTTOP:
                        if(bottomRight.x() - globalPoint.x() <= this->minimumWidth())
                        {
                            newRect.setX(topLeft.x());
                        }
                        else
                        {
                            newRect.setX(globalPoint.x());
                        }

                        if(bottomRight.y() - globalPoint.y() <= this->minimumHeight())
                        {
                            newRect.setY(topLeft.y());
                        }
                        else
                        {
                            newRect.setY(globalPoint.y());
                        }
                        break;
                     case RIGHTTOP:
                          if (globalPoint.x() - topLeft.x() >= this->minimumWidth())
                          {
                              newRect.setWidth(globalPoint.x() - topLeft.x());
                          }
                          else
                          {
                              newRect.setWidth(bottomRight.x() - topLeft.x());
                          }
                          if (bottomRight.y() - globalPoint.y() >= this->minimumHeight())
                          {
                              newRect.setY(globalPoint.y());
                          }
                          else
                          {
                              newRect.setY(topLeft.y());
                          }
                          break;
                     case LEFTBOTTOM:
                          if (bottomRight.x() - globalPoint.x() >= this->minimumWidth())
                          {
                              newRect.setX(globalPoint.x());
                          }
                          else
                          {
                              newRect.setX(topLeft.x());
                          }
                          if (globalPoint.y() - topLeft.y() >= this->minimumHeight())
                          {
                              newRect.setHeight(globalPoint.y() - topLeft.y());
                          }
                          else
                          {
                              newRect.setHeight(bottomRight.y() - topLeft.y());
                          }
                          break;
                      case RIGHTBOTTOM:
                          newRect.setWidth(globalPoint.x() - topLeft.x());
                          newRect.setHeight(globalPoint.y() - topLeft.y());
                          break;
                      default:
                          break;
                }
                this->setGeometry(newRect);
            }
            else
            {
                move(event->globalPos() - m_movePoint); //移动窗口
                event->accept();
            }
        }
    } 
}

mouseReleaseEvent

//鼠标释放事件
void MusicWidget::mouseReleaseEvent(QMouseEvent *event)  
{
    if (event->button() == Qt::LeftButton)
    {
        isLeftPressDown = false;
        if (dir != NONE)
        {
            this->releaseMouse(); //释放鼠标抓取
            this->setCursor(QCursor(Qt::ArrowCursor));
        }
    }
}