Qt实现在两个独立窗口之间拖放

末蓝、 2024-04-17 06:27 77阅读 0赞

# 一.拖放操作简介 #

**1.拖放的启动和结束**

1)、启动拖放：拖放通过调用QDrag::exec()函数而启动，这意味着在拖放操作结束之前，不会返回该函数，调用QDrag::exe()函数后，Qt拥有对拖动对象的所有权，并会在必要时将其删除

2)、结束拖放：当用户放下拖动或取消拖动操作时结束拖放。

3)、MIME类型使用QMimeData类来描述。MIME类型通常由剪贴板和拖放系统使用，以识别不同类型的数据

**2.拖放事件**

1)、QDragEnterEvent：拖动进入事件。当拖动操作进入部件时，发送该事件

2)、QDragMoveEvnet：拖动移动事件。当拖动操作正在进行时，发送该事件

3)、QDropEvent：放下事件。在完成拖放操作时发送该事件，即当用户在部件上放下一个对象时，发送此事件

4)、QDragLeaveEvent：当拖放操作离开部件时发送该事件

# 二.常用方法 #

setAcceptDrops(true); //设置能否拖动

setDragEnabled(true); //设置能否放置

setDropIndicatorShown(false);//显示拖放指示器

setDropAction(Qt::MoveAction) //设置拖动动作

QDrag::exe(Qt::MoveAction | Qt::CopyAction); //可能的拖放动作(移动、复制)

# 三.使用步骤 #

1)、调用setAcceptDrops()、setDragEnabled()函数以使该部件能接受拖放事件。

2)、启动拖放：通常在mousePressEvent()或mouseMoveEvent()函数中启动拖放，记住启动拖放就是调用QDrag对象的exec()函数，在此步把需要拖动的数据保存在QMimeData对象中。

3)、重新实现需要接受放下数据的部件的dragEnterEvent()事件处理函数。

4)、根据需要重新实现dragMoveEvent或dropEvent()函数

# 四.运行截图 #

![20190829224743611.gif][]

# 五.核心代码 #

#pragma once
    
    #include <QWidget>
    #include <QListWidget>
    
    QT_BEGIN_NAMESPACE
    class QDragEnterEvent;
    class QDropEvent;
    QT_END_NAMESPACE
    
    
    class DragWidget : public QListWidget
    {
    	Q_OBJECT
    
    public:
    	DragWidget(QWidget *parent = 0);
    	~DragWidget();
    
    protected:
    	void dragEnterEvent(QDragEnterEvent *event) override;
    	void dragMoveEvent(QDragMoveEvent *event) override;
    	void dropEvent(QDropEvent *event) override;
    	void mousePressEvent(QMouseEvent *event) override;
    
    private:
    	QListWidgetItem *m_curItem;
    
    };

#include "DragWidget.h"
    #include <QFont>
    #include <QDragEnterEvent>
    #include <QDropEvent>
    #include <QMouseEvent>
    #include <QMimeData>
    #include <QLabel>
    #include <QDrag>
    #include <QPainter>
    #include <QDebug>
    
    DragWidget::DragWidget(QWidget *parent)
    	: QListWidget(parent)
    	, m_curItem(nullptr)
    {
    	this->setViewMode(QListView::IconMode);
    	this->setSpacing(10);
    	this->setFixedSize(QSize(500, 500));
    	this->setAcceptDrops(true);
    	this->setDragEnabled(true);
    	this->setDropIndicatorShown(false);//显示拖放指示器
    	QFont font;
    	font.setFamily(QString::fromLocal8Bit("微软雅黑"));
    	font.setPointSize(12);
    	this->setFont(font);
    }
    
    DragWidget::~DragWidget()
    {
    	if(m_curItem)
    		delete m_curItem;
    }
    
    
    void DragWidget::dragEnterEvent(QDragEnterEvent *event)
    {
    	if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
    		if (event->source() == this) {
    			event->setDropAction(Qt::MoveAction);
    			event->accept();
    		}
    		else {
    			event->acceptProposedAction();
    
    		}
    		//qDebug() << "dragEnter: "<<event->dropAction();
    	}
    	else {
    		event->ignore();
    	}
    }
    void DragWidget::dragMoveEvent(QDragMoveEvent *event)
    {
    	if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
    		if (event->source() == this) {
    			event->setDropAction(Qt::MoveAction);
    			event->accept();
    			//qDebug() << "dragMove:   source  " << event->dropAction();
    
    		}
    		else {
    			event->acceptProposedAction();
    			//qDebug() << "dragMove:   nosource" << event->dropAction();
    		}
    	}
    	else {
    		event->ignore();
    	}
    }
    void DragWidget::dropEvent(QDropEvent *event)
    {
    	if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
    		QByteArray itemData = event->mimeData()->data("application/x-dnditemdata");
    		QString txt = event->mimeData()->text();
    		QDataStream dataStream(&itemData, QIODevice::ReadOnly);
    		QPixmap pixmap;
    		QPoint offset;
    		dataStream >> pixmap >> offset;
    
    		if (event->source() == this) {
    			event->setDropAction(Qt::MoveAction);
    			event->accept();
    
    			QListWidgetItem *curItem = this->itemAt(event->pos());
    			int iRow = this->row(curItem);
    			if (iRow < 0)
    				return;
    			else {
    				//m_curItem
    				delete takeItem(row(m_curItem));
    				this->insertItem(iRow, new QListWidgetItem(QIcon(pixmap), event->mimeData()->text()));
    			}
    				
                qDebug() << "dropEvent:   source" << event->dropAction();
    		}
    		else {
    			this->addItem(new QListWidgetItem(QIcon(pixmap), event->mimeData()->text()));
    			//event->acceptProposedAction();//建议的拖放动作
    			//event->accept();
    		}
    
    	}
    	else {
    		event->ignore();
    	}
    }
    void DragWidget::mousePressEvent(QMouseEvent *event)
    {
    	QListWidgetItem *currentItem = this->itemAt(event->pos());
    	m_curItem = this->itemAt(event->pos());
    	if (!currentItem)
    		return;
    	QLabel *child = new QLabel;
    	child->setGeometry(event->pos().x(), event->pos().y(), 50, 80);
    	if (!child)
    		return;
    
    	QIcon curIcon = currentItem->icon();
    	QPixmap pix = curIcon.pixmap(50, 80);
    	QByteArray itemData;
    	QDataStream dataStream(&itemData, QIODevice::WriteOnly);
    	dataStream << pix << QPoint(event->pos() - child->pos());
    	//! [1]
    
    	//! [2]
    	QMimeData *mimeData = new QMimeData;
    	mimeData->setData("application/x-dnditemdata", itemData);
    	mimeData->setText(currentItem->text());
    	//! [2]
    
    	//! [3]
    	QDrag *drag = new QDrag(this);
    	drag->setMimeData(mimeData);
    	drag->setPixmap(pix);
    	drag->setHotSpot(event->pos()- child->pos()+QPoint(20,20));
    	//! [3]
    
    	QPixmap tempPixmap = pix;
    	QPainter painter;
    	painter.begin(&tempPixmap);
    	painter.fillRect(pix.rect(), QColor(127, 127, 127, 127));
    	painter.end();
    
    	child->setPixmap(tempPixmap);
    	child->setText(currentItem->text());
    	//参数1可能动作为移动或者复制,参数2建议动作为复制
    
    	Qt::DropAction dropAction;
    	dropAction = drag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction);
    
    	if (dropAction == Qt::MoveAction) {
    		//delete takeItem(row(currentItem));
    		return;
    	}
    	else if (dropAction == Qt::CopyAction) {
    		//delete takeItem(row(currentItem));
    	}
    	else
    	{
    		if (drag->target())
    			delete takeItem(row(currentItem));
    	}
    	qDebug() << "exec action" << dropAction;
    	qDebug() << "drag target " << drag->target();
    		//return;
    }

# 六.完整工程 #

[https://download.csdn.net/download/wzz953200463/11615903][https_download.csdn.net_download_wzz953200463_11615903]

[20190829224743611.gif]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/5a867982d44349e89f1e36abf6626e4b.gif
[https_download.csdn.net_download_wzz953200463_11615903]: https://download.csdn.net/download/wzz953200463/11615903