实现在一个窗口内随意拖动一个控件功能

头文件 MyDragWidget.h

#ifndef MYDRAGWIDGET_H
#define MYDRAGWIDGET_H

#include <QWidget>

class MyDragWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MyDragWidget(PointInfo ptInfo,QWidget *parent = nullptr);
    void mousePressEvent(QMouseEvent *event) override;
    void mouseMoveEvent(QMouseEvent *event) override;
    void mouseReleaseEvent(QMouseEvent *event) override;

signals:

public slots:

private:
    void user_drag_out_disposal();

private:
    QPoint m_mouse_point;
    QPoint m_widget_point;
    bool m_bMove;

private:
    QWidget* m_Parent;
};

#endif // MYDRAGWIDGET_H

源文件 MyDragWidget.cpp

#include "MyDragWidget.h"

#include <QMouseEvent>
#include <QVBoxLayout>


MyDragWidget::MyDragWidget(PointInfo ptInfo, QWidget *parent) : QWidget(parent)/*, m_point_info(ptInfo)*/
{
    if(parent)
        m_Parent = parent;

    m_bMove = false;
}

void MyDragWidget::mousePressEvent(QMouseEvent *event)
{
    if(event->button() == Qt::LeftButton)
    {
        m_bMove = true;
        m_mouse_point = event->globalPos();                 // 鼠标世界坐标
        m_widget_point = this->frameGeometry().topLeft();   // 窗口世界坐标
    }
}

void MyDragWidget::mouseMoveEvent(QMouseEvent *event)
{
    if(event->buttons() & Qt::LeftButton)
    {
        QPoint pt = event->globalPos() - m_mouse_point;
        this->move(m_widget_point + pt);
        user_drag_out_disposal();
    }
}

void MyDragWidget::mouseReleaseEvent(QMouseEvent *event)
{
    if(event->button() == Qt::LeftButton)
        m_bMove = false;
}

void MyDragWidget::user_drag_out_disposal()
{
    int width = m_Parent->width() - this->width();
    int height = m_Parent->height() - this->height();

    int x = this->x();
    int y = this->y();

    if(m_Parent)
    {
        if(x <= 0)
        {
            if(y <= 0)
            {
                QPoint pt(0, 0);
                this->move(pt);
            }
            else if( y > 0 && y < height)
            {
                QPoint pt(0, y);
                this->move(pt);
            }
            else if(y >= height)
            {
                QPoint pt(0, height);
                this->move(pt);
            }
        }
        else if( x > 0 && x < width )
        {
            if(y <= 0)
            {
                QPoint pt(x, 0);
                this->move(pt);
            }
            else if( y > 0 && y < height)
            {
                QPoint pt(x, y);
                this->move(pt);
            }
            else if(y >= height)
            {
                QPoint pt(x, height);
                this->move(pt);
            }
        }
        else if( x >= width)
        {
            if(y <= 0)
            {
                QPoint pt(width, 0);
                this->move(pt);
            }
            else if( y > 0 && y < height)
            {
                QPoint pt(width, y);
                this->move(pt);
            }
            else if(y >= height)
            {
                QPoint pt(width, height);
                this->move(pt);
            }
        }
    }

}

main文件 main.cpp

#include "MyWidget.h"

#include <QApplication>
#include <QVBoxLayout>
#include <QLabel>


#include "MyDragWidget.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QWidget w;
    QLabel* label = new QLabel(&w);
    label->resize(800, 600);

    MyDragWidget mw(pt, label);
    mw.setGeometry(30, 30, 80, 100);

    mw.setStyleSheet("border:1px solid #FF00FF;border-radius:5px;");
    mw.setStyleSheet("background:#642100;");

    w.show();
    return a.exec();
}