1.效果：

2. 主要实现步骤：

设置窗口 flag：

this->setWindowFlags(Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);

 创建变量存储位置

QPoint m_dragPosition;

对鼠标左键按下和移动事件做处理

void DraggableDialog::mousePressEvent(QMouseEvent *event)   {
    isDragging = true;
    dragPos = event->globalPos() - frameGeometry().topLeft();
}

// 鼠标移动事件，实现拖动
void DraggableDialog::mouseMoveEvent(QMouseEvent *event)   {
    if (isDragging) {
        move(event->globalPos() - dragPos);
    }
}

// 鼠标释放事件，结束拖动
void DraggableDialog::mouseReleaseEvent(QMouseEvent *event)   {
    isDragging = false;
}

3 .code:

#ifndef DRAGGABLEDIALOG_H
#define DRAGGABLEDIALOG_H

#include <QDialog>
#include <QMouseEvent>
namespace Ui {
class DraggableDialog;
}

class DraggableDialog : public QDialog
{
    Q_OBJECT

public:
    explicit DraggableDialog(QWidget *parent = nullptr);
    ~DraggableDialog();

protected:
    // 鼠标按下事件，记录点击位置
    void mousePressEvent(QMouseEvent *event) override;

    // 鼠标移动事件，实现拖动
    void mouseMoveEvent(QMouseEvent *event) override;

    // 鼠标释放事件，结束拖动
    void mouseReleaseEvent(QMouseEvent *event) override ;

private:
    bool isDragging;
    QPoint dragPos;

private:
    Ui::DraggableDialog *ui;
};

#endif // DRAGGABLEDIALOG_H

cpp

#include "draggabledialog.h"
#include "ui_draggabledialog.h"

DraggableDialog::DraggableDialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::DraggableDialog)
{
    ui->setupUi(this);
    // 设置窗口无边框
    this->setWindowFlags(Qt::FramelessWindowHint);
    setToolTip("窗口无边框,可拖动");
}

DraggableDialog::~DraggableDialog()
{
    delete ui;
}
void DraggableDialog::mousePressEvent(QMouseEvent *event)   {
    isDragging = true;
    dragPos = event->globalPos() - frameGeometry().topLeft();
}

// 鼠标移动事件，实现拖动
void DraggableDialog::mouseMoveEvent(QMouseEvent *event)   {
    if (isDragging) {
        move(event->globalPos() - dragPos);
    }
}

// 鼠标释放事件，结束拖动
void DraggableDialog::mouseReleaseEvent(QMouseEvent *event)   {
    isDragging = false;
}

main

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
 
    DraggableDialog dialog;
    dialog.show();
 
    return app.exec();
}