qt 无边框窗体的拖动和改变大小

参考：https://www.cnblogs.com/xufeiyang/p/3313104.html

这个类是关于无边框窗体的拖动和改变大小的。如果是QWidget，请将继承类改为QWidget，并将源文件的QDialog用QWidget替换。

我曾想将这个类作为中间类，让窗口类继承此类，这样如果有多个无边框窗口，就不用每个窗口都作重复改变了，但是没有成功。由于时间关系，没再做深入研究。以后有时间再说吧。

头文件：

#ifndef CustomFrameLessWidget_H
#define CustomFrameLessWidget_H

#include <QRect>
#include <QDialog>
#include <QWidget>
#include <QMouseEvent>

#define PADDING 2
enum Direction { UP=0, DOWN=1, LEFT, RIGHT, LEFTTOP, LEFTBOTTOM, RIGHTBOTTOM, RIGHTTOP, NONE };

class CustomFrameLessWidget : public QDialog
{
    Q_OBJECT
public:
    CustomFrameLessWidget(QWidget* parent = NULL);
    void region(const QPoint &cursorGlobalPoint);
protected:
    void mouseReleaseEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void mousePressEvent(QMouseEvent *event);
public:
    bool isLeftPressDown;  // 判断左键是否按下
    QPoint dragPosition;   // 窗口移动拖动时需要记住的点
    Direction dir;        // 窗口大小改变时，记录改变方向

};

#endif // CustomFrameLessWidget_H

源文件：

#include "CustomFrameLessWidget.h"

CustomFrameLessWidget::CustomFrameLessWidget(QWidget* parent):QDialog(parent)
{
    isLeftPressDown = false;
    this->dir = NONE;
    this->setMinimumHeight(100);
    this->setMinimumWidth(150);
    this->setWindowFlags(Qt::FramelessWindowHint|Qt::WindowSystemMenuHint); // 设置成无边框对话框
    this->setMouseTracking(true);// 追踪鼠标
//    this->setStyleSheet("QDialog{background:url(:/bg_main.png)}"); // 设置样式背景色，可有可无
}

void CustomFrameLessWidget::region(const QPoint &cursorGlobalPoint)
{
    // 获取窗体在屏幕上的位置区域，tl为topleft点，rb为rightbottom点
    QRect rect = this->rect();
    QPoint tl = mapToGlobal(rect.topLeft());
    QPoint rb = mapToGlobal(rect.bottomRight());

    int x = cursorGlobalPoint.x();
    int y = cursorGlobalPoint.y();

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

void CustomFrameLessWidget::mouseReleaseEvent(QMouseEvent *event)
{
    if(event->button() == Qt::LeftButton) {
        isLeftPressDown = false;
        if(dir != NONE) {
            this->releaseMouse();
            this->setCursor(QCursor(Qt::ArrowCursor));
        }
    }
}

void CustomFrameLessWidget::mousePressEvent(QMouseEvent *event)
{
    switch(event->button()) {
    case Qt::LeftButton:
        isLeftPressDown = true;
        if(dir != NONE) {
            this->mouseGrabber();
        } else {
            dragPosition = event->globalPos() - this->frameGeometry().topLeft();
        }
        break;
    case Qt::RightButton:
        this->close();
        break;
    default:
        QDialog::mousePressEvent(event);
    }

}

void CustomFrameLessWidget::mouseMoveEvent(QMouseEvent *event)
{
    QPoint gloPoint = event->globalPos();
    QRect rect = this->rect();
    QPoint tl = mapToGlobal(rect.topLeft());
    QPoint rb = mapToGlobal(rect.bottomRight());

    if(!isLeftPressDown) {
        this->region(gloPoint);
    } else {

        if(dir != NONE) {
            QRect rMove(tl, rb);

            switch(dir) {
            case LEFT:
                if(rb.x() - gloPoint.x() <= this->minimumWidth())
                    rMove.setX(tl.x());
                else
                    rMove.setX(gloPoint.x());
                break;
            case RIGHT:
                rMove.setWidth(gloPoint.x() - tl.x());
                break;
            case UP:
                if(rb.y() - gloPoint.y() <= this->minimumHeight())
                    rMove.setY(tl.y());
                else
                    rMove.setY(gloPoint.y());
                break;
            case DOWN:
                rMove.setHeight(gloPoint.y() - tl.y());
                break;
            case LEFTTOP:
                if(rb.x() - gloPoint.x() <= this->minimumWidth())
                    rMove.setX(tl.x());
                else
                    rMove.setX(gloPoint.x());
                if(rb.y() - gloPoint.y() <= this->minimumHeight())
                    rMove.setY(tl.y());
                else
                    rMove.setY(gloPoint.y());
                break;
            case RIGHTTOP:
                rMove.setWidth(gloPoint.x() - tl.x());
                rMove.setY(gloPoint.y());
                break;
            case LEFTBOTTOM:
                rMove.setX(gloPoint.x());
                rMove.setHeight(gloPoint.y() - tl.y());
                break;
            case RIGHTBOTTOM:
                rMove.setWidth(gloPoint.x() - tl.x());
                rMove.setHeight(gloPoint.y() - tl.y());
                break;
            default:
                break;
            }
            this->setGeometry(rMove);
        } else {
            move(event->globalPos() - dragPosition);
            event->accept();
        }
    }
    QDialog::mouseMoveEvent(event);
}