qt自定义标题栏，纯代码实现，拿来即用，初始化列表时传入父窗口的this指针

// 头文件
#ifndef TITLEBAR_H
#define TITLEBAR_H

#include <QWidget>
#include <QPoint>  //坐标点
#include <QMouseEvent> //鼠标事件

class TitleBar : public QWidget
{
    Q_OBJECT
public:
    explicit TitleBar(QWidget *parent = nullptr);
    // 移动窗口的变量;
    bool m_isPressed; //鼠标按下标志
    QPoint m_startMovePos;  //开始移动的坐标点
protected:

    void mouseMoveEvent(QMouseEvent* event);
    void mousePressEvent(QMouseEvent* event);
    void mouseReleaseEvent(QMouseEvent* event);
signals:

private:
    QWidget* m_parent;
};

#endif // TITLEBAR_H

// 源文件
#include "titlebar.h"
#include <qDebug>
TitleBar::TitleBar(QWidget* parent)
    : QWidget(parent)
    , m_isPressed(false)  //初始化鼠标按下标志为 false
    , m_parent(parent)

{
    // 设置唯一标识符
    this->setObjectName("TitleBar");
    // 拥有子窗口自己的样式
    setAttribute(Qt::WA_StyledBackground);
}

//鼠标移动事件
void TitleBar::mouseMoveEvent(QMouseEvent* event)
{
    //判断鼠标是否按下
    if (m_isPressed)
    {
        QPoint movePoint = event->globalPos() - m_startMovePos;
        QPoint widgetPos = m_parent->pos();
        m_startMovePos = event->globalPos();
        if(m_parent)
        {
            m_parent->move(widgetPos.x() + movePoint.x(), widgetPos.y() + movePoint.y());
        }
    }
}

//鼠标按下事件
void TitleBar::mousePressEvent(QMouseEvent* event)
{
     //获取鼠标相对于软件的坐标
    QPoint _mouseCurrent_software = event->pos();
     //获取鼠标相对于桌面的坐标
    QPoint _mouseCurrent_windows = event->globalPos();

    //标题栏的宽度
    int _titleBar_width = this->width();
    //标题栏的高度
    int _titleBar_height = this->height();
    if (!isMaximized())
    {
        //判断鼠标是否在标题栏范围内
        if (_mouseCurrent_software.x()<= _titleBar_width&&_mouseCurrent_software.y()<=_titleBar_height)
        {
            m_isPressed = true;
            m_startMovePos = event->globalPos();
        }
        else
        {
            m_isPressed = false;
        }
    }
}


//鼠标释放事件
void TitleBar::mouseReleaseEvent(QMouseEvent* event)
{
    m_isPressed = false;
}

// 使用
#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QWidget(parent)
    , m_titleBar(new TitleBar(this))
{
    // 去掉标题栏和边框
    setWindowFlags(Qt::Window | Qt::FramelessWindowHint);

    m_titleBar->show();

}

MainWindow::~MainWindow() {}

效果： 鼠标左键按住移动，跟随鼠标移动。