Qt无边框窗体模仿Win32标准窗体鼠标拖拽效果

本文介绍如何针对Qt的无边框窗体（即setWindowFlags(Qt::FramelessWindowHint);）实现鼠标拖拽标题栏移动窗体位置、鼠标拖拽窗体四周边框改变窗体大小的行为。

一、为所有控件添加MouseTracking

在Qt中，控件默认只有在至少有一个鼠标按键被按下的情况下，控件才能捕获鼠标的移动事件。针对我们想要模拟“鼠标拖拽窗体四周边框改变窗体大小的行为”，需要能够实时获得鼠标的移动事件，以便在鼠标移动到窗体四周时能做出相应的处理。虽然我们可以对所有控件都添加上“鼠标追踪”属性（setMouseTracking(true);），但一个个控件添加太麻烦，下面的setAllWidgetMouseTracking函数，可以递归地为父widget下的所有控件添加“鼠标追踪”属性。一般情况我们只需要将centralWidget传给setAllWidgetMouseTracking函数即可。

void BaseMainWindow::setAllWidgetMouseTracking(QWidget *widget) {
	if(!widget)
		return;
	widget->setMouseTracking(true);
	QObjectList list = widget->children();
	foreach(QObject *obj, list) {
		if(obj->metaObject()->className() == QStringLiteral("QWidget")) {
			QWidget* w = (QWidget*)obj;
			qDebug() << w->objectName();
			w->setMouseTracking(true);
			setAllWidgetMouseTracking(w);
		}
	}
}

二、实现原理

1. 模拟鼠标拖拽标题栏移动窗体位置
   通过void setTitleWidget(const QString &widgetName);接口设置一个widget名称，当鼠标左键在该widget区域按下，并保持着按下状态，就会启用鼠标移动则窗体位置跟着移动的效果。
2. 模拟鼠标拖拽窗体四周边框改变窗体大小
   通过void setEnableResize(bool b);接口来启动该功能。
   鼠标移动到窗体边缘附件时（具体值由m_iResizeRegionPadding来设置），鼠标形状会变成Qt::SizeVerCursor，此时用户再按下鼠标左键，移动鼠标就可以改变窗体大小。

BaseMainWindow .h

#pragma once

#include <QtWidgets/QMainWindow>
#include <QtWidgets/QWidget>

class BaseMainWindow : public QMainWindow {
	Q_OBJECT
public:
	enum Direction {
		UP = 0,
		DOWN = 1,
		LEFT,
		RIGHT,
		LEFTTOP,
		LEFTBOTTOM,
		RIGHTBOTTOM,
		RIGHTTOP,
		NONE
	};

	BaseMainWindow(QWidget *parent = Q_NULLPTR);
	virtual ~BaseMainWindow();
	void setTitleWidget(const QString &widgetName);
	void setEnableResize(bool b);
	void setAllWidgetMouseTracking(QWidget *widget);
	
protected:
    bool eventFilter(QObject *target, QEvent *event);
    void mouseDoubleClickEvent(QMouseEvent *event) override;
	void mousePressEvent(QMouseEvent *event) override;
	void mouseMoveEvent(QMouseEvent *event) override;
	void mouseReleaseEvent(QMouseEvent *event) override;
protected:
	void region(const QPoint &cursorGlobalPoint);
protected:
	bool m_bLeftPressed;

	Direction m_Direction;
	const int m_iResizeRegionPadding;


	bool m_bEnableResize;
	QPoint m_DragPos;
	QString m_strTitleWidget;
};

BaseMainWindow.cpp

#include "stdafx.h"
#include "BaseMainWindow.h"


BaseMainWindow::BaseMainWindow(QWidget *parent) : QMainWindow(parent),
m_bLeftPressed(false),
m_bEnableResize(false),
m_Direction(Direction::NONE),
m_iResizeRegionPadding(2) {

}

BaseMainWindow::~BaseMainWindow() {
}

void BaseMainWindow::setTitleWidget(const QString &widgetName) {
	m_strTitleWidget = widgetName;
}

void BaseMainWindow::setEnableResize(bool b) {
	m_bEnableResize = b;
}

void BaseMainWindow::mousePressEvent(QMouseEvent *event) {
	if(event->button() == Qt::LeftButton) {
		m_bLeftPressed = true;
		if(m_Direction != Direction::NONE) {
			this->mouseGrabber();
		}
		else if(m_strTitleWidget.length() > 0) {
			QWidget *action = QApplication::widgetAt(event->globalPos());
			if(action) {
				if(action->objectName() == m_strTitleWidget) {
					m_DragPos = event->globalPos() - this->frameGeometry().topLeft();
				}
			}
		}
	}
	return QWidget::mousePressEvent(event);
}

void BaseMainWindow::mouseMoveEvent(QMouseEvent *event) {
	QPoint globalPoint = event->globalPos();
	if(m_bLeftPressed) {
		if(m_Direction != NONE) {
			QRect rect = this->rect();
			QPoint tl = mapToGlobal(rect.topLeft());
			QPoint rb = mapToGlobal(rect.bottomRight());

			QRect rMove(tl, rb);

			switch(m_Direction) {
				case LEFT:
					if(rb.x() - globalPoint.x() <= this->minimumWidth())
						rMove.setX(tl.x());
					else
						rMove.setX(globalPoint.x());
					break;
				case RIGHT:
					rMove.setWidth(globalPoint.x() - tl.x());
					break;
				case UP:
					if(rb.y() - globalPoint.y() <= this->minimumHeight())
						rMove.setY(tl.y());
					else
						rMove.setY(globalPoint.y());
					break;
				case DOWN:
					rMove.setHeight(globalPoint.y() - tl.y());
					break;
				case LEFTTOP:
					if(rb.x() - globalPoint.x() <= this->minimumWidth())
						rMove.setX(tl.x());
					else
						rMove.setX(globalPoint.x());
					if(rb.y() - globalPoint.y() <= this->minimumHeight())
						rMove.setY(tl.y());
					else
						rMove.setY(globalPoint.y());
					break;
				case RIGHTTOP:
					rMove.setWidth(globalPoint.x() - tl.x());
					rMove.setY(globalPoint.y());
					break;
				case LEFTBOTTOM:
					rMove.setX(globalPoint.x());
					rMove.setHeight(globalPoint.y() - tl.y());
					break;
				case RIGHTBOTTOM:
					rMove.setWidth(globalPoint.x() - tl.x());
					rMove.setHeight(globalPoint.y() - tl.y());
					break;
				default:

					break;
			}
			this->setGeometry(rMove);
		}
		else {
			this->move(event->globalPos() - m_DragPos);
			event->accept();
		}
	}
	else {
		region(globalPoint);
	}
   
	return QWidget::mouseMoveEvent(event);
}

void BaseMainWindow::region(const QPoint &cursorGlobalPoint) {
	if(!m_bEnableResize)
		return;
	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() + m_iResizeRegionPadding >= x && tl.x() <= x && tl.y() + m_iResizeRegionPadding >= y && tl.y() <= y) {
		// 左上角
		m_Direction = Direction::LEFTTOP;
		this->setCursor(QCursor(Qt::SizeFDiagCursor));
	}
	else if(x >= rb.x() - m_iResizeRegionPadding && x <= rb.x() && y >= rb.y() - m_iResizeRegionPadding && y <= rb.y()) {
		// 右下角
		m_Direction = Direction::RIGHTBOTTOM;
		this->setCursor(QCursor(Qt::SizeFDiagCursor));
	}
	else if(x <= tl.x() + m_iResizeRegionPadding && x >= tl.x() && y >= rb.y() - m_iResizeRegionPadding && y <= rb.y()) {
		//左下角
		m_Direction = Direction::LEFTBOTTOM;
		this->setCursor(QCursor(Qt::SizeBDiagCursor));
	}
	else if(x <= rb.x() && x >= rb.x() - m_iResizeRegionPadding && y >= tl.y() && y <= tl.y() + m_iResizeRegionPadding) {
		// 右上角
		m_Direction = Direction::RIGHTTOP;
		this->setCursor(QCursor(Qt::SizeBDiagCursor));
	}
	else if(x <= tl.x() + m_iResizeRegionPadding && x >= tl.x()) {
		// 左边
		m_Direction = Direction::LEFT;
		this->setCursor(QCursor(Qt::SizeHorCursor));
	}
	else if(x <= rb.x() && x >= rb.x() - m_iResizeRegionPadding) {
		// 右边
		m_Direction = Direction::RIGHT;
		this->setCursor(QCursor(Qt::SizeHorCursor));
	}
	else if(y >= tl.y() && y <= tl.y() + m_iResizeRegionPadding) {
		// 上边
		m_Direction = Direction::UP;
		this->setCursor(QCursor(Qt::SizeVerCursor));
	}
	else if(y <= rb.y() && y >= rb.y() - m_iResizeRegionPadding) {
		// 下边
		m_Direction = Direction::DOWN;
		this->setCursor(QCursor(Qt::SizeVerCursor));
	}
	else {
		// 默认
		m_Direction = Direction::NONE;
		this->setCursor(QCursor(Qt::ArrowCursor));
	}
}

void BaseMainWindow::mouseReleaseEvent(QMouseEvent *event) {
	m_bLeftPressed = false;
	if(m_Direction != NONE) {
		this->releaseMouse();
		this->setCursor(QCursor(Qt::ArrowCursor));
	}
	return QWidget::mouseReleaseEvent(event);
}

void BaseMainWindow::setAllWidgetMouseTracking(QWidget *widget) {
	if(!widget)
		return;
	widget->setMouseTracking(true);
	QObjectList list = widget->children();
	foreach(QObject *obj, list) {
		if(obj->metaObject()->className() == QStringLiteral("QWidget")) {
			QWidget* w = (QWidget*)obj;
			qDebug() << w->objectName();
			w->setMouseTracking(true);
			setAllWidgetMouseTracking(w);
		}
	}
}