2020.02.27

想要代码，留邮箱吧。或者到https://download.csdn.net/download/XuePiaoFei1/12195991下载，或者https://files-cdn.cnblogs.com/files/warmlight/NewProject.rar。

近来Qt开发时可能遇到这样的需求：两个（或多个）矩形，要用直线将它们连接起来，之后还要把它们保存到xml中，并且能够还原。

类似于下图：

首先想到的就是Qt自带的demo：diagramscene。因为demo中有箭头方向，开始节点和结束节点，连坐标都已经有了，保存还原都可以完成。但是，demo的直线不是竖直或水平的，所以肯定要对demo进行修改。（扯淡了，demo肯定不会符合个人的需求的，无论如何都要修改的。）

刚用Qt不久，网络上也搜不到类似的问题，也许是自己找不到，只能寄希望于Qt的demo，限制了自己的思想。可是目前没有更好的办法。

我的工程有几个要点，要能够保存和还原，箭头的首尾节点肯定要确定，或者说首尾节点的坐标一定要知道。

demo中的基本元素够了，我想只对arrow类作修改，希望能达到目标。

我先把我改造后的arrow类贴出来，然后再试图分析一下。

头文件：

 /****************************************************************************

 **

 ** Copyright (C) 2016 The Qt Company Ltd.

 ** Contact: https://www.qt.io/licensing/

 **

 ** This file is part of the examples of the Qt Toolkit.

 **

 ** $QT_BEGIN_LICENSE:BSD$

 ** Commercial License Usage

 ** Licensees holding valid commercial Qt licenses may use this file in

 ** accordance with the commercial license agreement provided with the

 ** Software or, alternatively, in accordance with the terms contained in

 ** a written agreement between you and The Qt Company. For licensing terms

 ** and conditions see https://www.qt.io/terms-conditions. For further

 ** information use the contact form at https://www.qt.io/contact-us.

 **

 ** BSD License Usage

 ** Alternatively, you may use this file under the terms of the BSD license

 ** as follows:

 **

 ** "Redistribution and use in source and binary forms, with or without

 ** modification, are permitted provided that the following conditions are

 ** met:

 **   * Redistributions of source code must retain the above copyright

 **     notice, this list of conditions and the following disclaimer.

 **   * Redistributions in binary form must reproduce the above copyright

 **     notice, this list of conditions and the following disclaimer in

 **     the documentation and/or other materials provided with the

 **     distribution.

 **   * Neither the name of The Qt Company Ltd nor the names of its

 **     contributors may be used to endorse or promote products derived

 **     from this software without specific prior written permission.

 **

 **

 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."

 **

 ** $QT_END_LICENSE$

 **

 ****************************************************************************/

 #ifndef ARROW_H

 #define ARROW_H

 #include <QGraphicsLineItem>

 #include "diagramitem.h"

 QT_BEGIN_NAMESPACE

 class QGraphicsPolygonItem;

 class QGraphicsLineItem;

 class QGraphicsScene;

 class QRectF;

 class QGraphicsSceneMouseEvent;

 class QPainterPath;

 QT_END_NAMESPACE

 enum LineType {

     lineType1 = ,  //横竖

     lineType2,      //竖横

     lineType3,      //横竖横

     lineType4       //竖横竖

 };

 //! [0]

 class Arrow : public QGraphicsLineItem

 {

 public:

     enum { Type = UserType +  };

     Arrow(DiagramItem *startItem, DiagramItem *endItem,

       QGraphicsItem *parent = );

     ~Arrow() {m_bDeleteFlag = true;}

     int type() const override { return Type; }

     QRectF boundingRect() const override;

     QPainterPath shape() const override;

     void setColor(const QColor &color) { myColor = color; }

     DiagramItem *startItem() const { return myStartItem; }

     DiagramItem *endItem() const { return myEndItem; }

     void setItemId(QString startItemId ,QString startEndId);

     void updatePosition();

     QString getStartId(){return startId;}

     QString getEndId(){return endId;}

     void setStartItem(DiagramItem *startItem){ myStartItem = startItem; }

     void setEndItem(DiagramItem *endItem){ myEndItem = endItem; }

     void setArrowFlag(bool IsArrow){bisArrow = IsArrow;}

     bool getArrowFlag(){return bisArrow;}

     bool getDeleteFlage() {return m_bDeleteFlag;}

     void DrawArrow(QPainter *painter, QPointF startPt, QPointF endPt, bool bArrow);

     void ThreeLine(QPainter *painter, QPointF startPt, QPointF endPt);//三段线

     void TwoLine(QPainter *painter, QPointF startPt, QPointF endPt); //两段线

     //void SetLineStyle(bool bVhvLine);//线段的折线风格

     //void SetLineType(int nLineType);//线段的数量

     void SetLineType(LineType lineType);

     int GetLineType() {return m_lineType;}

     void DrawLine(QPainter *painter, QPointF startPt, QPointF endPt);

 protected:

     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = ) override;

 private:

     DiagramItem *myStartItem;

     DiagramItem *myEndItem;

     QColor myColor;

     QPolygonF arrowHead;

     QString startId;

     QString endId;

     bool bisArrow;

     bool m_bDeleteFlag;//

     LineType m_lineType;

     //bool m_bVhvLine;//true三段线，竖横竖; false三段线 横竖横

     //bool m_bVhLine;// true两段线 竖横; false 两段线 横竖

     //int m_nLineType;//2-2段线，3-3段线

 };

 inline void Arrow::setItemId(QString startItemId ,QString startEndId){

     startId = startItemId;

     endId = startEndId;

 }

 //! [0]

 #endif // ARROW_H

cpp文件：

 /****************************************************************************

 **

 ** Copyright (C) 2016 The Qt Company Ltd.

 ** Contact: https://www.qt.io/licensing/

 **

 ** This file is part of the examples of the Qt Toolkit.

 **

 ** $QT_BEGIN_LICENSE:BSD$

 ** Commercial License Usage

 ** Licensees holding valid commercial Qt licenses may use this file in

 ** accordance with the commercial license agreement provided with the

 ** Software or, alternatively, in accordance with the terms contained in

 ** a written agreement between you and The Qt Company. For licensing terms

 ** and conditions see https://www.qt.io/terms-conditions. For further

 ** information use the contact form at https://www.qt.io/contact-us.

 **

 ** BSD License Usage

 ** Alternatively, you may use this file under the terms of the BSD license

 ** as follows:

 **

 ** "Redistribution and use in source and binary forms, with or without

 ** modification, are permitted provided that the following conditions are

 ** met:

 **   * Redistributions of source code must retain the above copyright

 **     notice, this list of conditions and the following disclaimer.

 **   * Redistributions in binary form must reproduce the above copyright

 **     notice, this list of conditions and the following disclaimer in

 **     the documentation and/or other materials provided with the

 **     distribution.

 **   * Neither the name of The Qt Company Ltd nor the names of its

 **     contributors may be used to endorse or promote products derived

 **     from this software without specific prior written permission.

 **

 **

 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."

 **

 ** $QT_END_LICENSE$

 **

 ****************************************************************************/

 #include "arrow.h"

 #include <qmath.h>

 #include <QPen>

 #include <QPainter>

 #include <QDebug>

 //! [0]

 Arrow::Arrow(DiagramItem *startItem, DiagramItem *endItem, QGraphicsItem *parent)

     : QGraphicsLineItem(parent)

 {

     m_bDeleteFlag = false;//20191121 sdl

     myStartItem = startItem;

     myEndItem = endItem;

     setFlag(QGraphicsItem::ItemIsSelectable, true);

     myColor = Qt::black;

     setPen(QPen(myColor, , Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));

     bisArrow = true;

     if(myStartItem){startId = myStartItem->getItemId();}

     if(myEndItem){endId = myEndItem->getItemId();}

     m_lineType = LineType::lineType1;

 }

 //! [0]

 //! [1]

 QRectF Arrow::boundingRect() const

 {

     qreal extra = (pen().width() + ) / 2.0;

     return QRectF(line().p1(), QSizeF(line().p2().x() - line().p1().x(),

                                       line().p2().y() - line().p1().y()))

         .normalized()

         .adjusted(-extra, -extra, extra, extra);

 }

 //! [1]

 //! [2]

 QPainterPath Arrow::shape() const

 {

     QPainterPath path = QGraphicsLineItem::shape();

     path.addPolygon(arrowHead);

     return path;

 }

 //! [2]

 //! [3]

 void Arrow::updatePosition()

 {

     QPointF endPt = mapFromItem(myEndItem, , );

     QLineF line(mapFromItem(myStartItem, , ), endPt);

     setLine(line);

 }

 //! [3]

 //! [4]

 void Arrow::paint(QPainter *painter, const QStyleOptionGraphicsItem *,

           QWidget *)

 {

     if(myStartItem == NULL || myEndItem == NULL) return;

     if(myStartItem->GetDeleteFlag() || myEndItem->GetDeleteFlag()) return;

     if (myStartItem->collidesWithItem(myEndItem))

         return;

     QPointF start = myStartItem->pos();

     QPointF end = myEndItem->pos();

     if(qFuzzyCompare(start.x(), end.x())){ //如果在同一竖直或水平线时，直接连接两节点中心点

         DrawArrow(painter, start, end, true);

         return;

     }

     if (qFuzzyCompare(start.y(), end.y())) {

         DrawArrow(painter, start, end, true);

         return;

     }

     DrawLine(painter, start, end);

 //    if(m_nLineType == 2){

 //        TwoLine(painter, start, end);

 //    }

 //    else if (m_nLineType == 3) {

 //        ThreeLine(painter, start, end);

 //    }

 }

 //! [7]

 void Arrow::DrawArrow(QPainter *painter, QPointF startPt, QPointF endPt, bool bArrow)

 {

     if(endPt == QPointF(, )){

         return;

     }

     QPen myPen = pen();

     myPen.setColor(myColor);

     qreal arrowSize = ;

     painter->setPen(myPen);

     painter->setBrush(myColor);

 //! [4] //! [5]

     QLineF centerLine(startPt, endPt);

     QPolygonF endPolygon;

     endPolygon = myEndItem->polygon();

     QPointF p1 = endPolygon.first() + endPt;

     QPointF p2;

     QPointF intersectPoint;

     QLineF polyLine;

     for (int i = ; i < endPolygon.count(); ++i) {

         p2 = endPolygon.at(i) + endPt;

         polyLine = QLineF(p1, p2);

         QLineF::IntersectType intersectType =

             polyLine.intersect(centerLine, &intersectPoint);

         if (intersectType == QLineF::BoundedIntersection)

             break;

         p1 = p2;

     }

     setLine(QLineF(endPt, startPt/*myStartItem->pos()*/));

 //! [5] //! [6]

     if (bArrow){

         setLine(QLineF(intersectPoint, startPt/*myStartItem->pos()*/));//如果是箭头所在的线

     }

     double angle = std::atan2(-line().dy(), line().dx());

     QPointF arrowP1 = line().p1() + QPointF(sin(angle + M_PI / ) * arrowSize,

                                     cos(angle + M_PI / ) * arrowSize);

     QPointF arrowP2 = line().p1() + QPointF(sin(angle + M_PI - M_PI / ) * arrowSize,

                                     cos(angle + M_PI - M_PI / ) * arrowSize);

     arrowHead.clear();

     arrowHead << line().p1() << arrowP1 << arrowP2;

 //! [6] //! [7]

     painter->drawLine(line());

     //是否画箭头

     if(bArrow){

         painter->drawPolygon(arrowHead);

     }

     if (isSelected()) {

         painter->setPen(QPen(myColor, , Qt::DashLine));

         QLineF myLine = line();

         myLine.translate(, 4.0);

         painter->drawLine(myLine);

         myLine.translate(,-8.0);

         painter->drawLine(myLine);

     }

 }

 void Arrow::ThreeLine(QPainter *painter, QPointF start, QPointF end)

 {

     if(m_lineType == LineType::lineType4){

         qreal midY = (start.y() + end.y()) / ;

         QPointF startPt = myStartItem->pos();

         QPointF endPt = myEndItem->pos();

         endPt.setX(startPt.x());

         endPt.setY(midY);

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt.setX(myEndItem->pos().x());

         endPt.setY(startPt.y());

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt = myEndItem->pos();

         DrawArrow(painter, startPt, endPt, true);

     }

     else if(m_lineType == LineType::lineType3){

         qreal midX = (start.x() + end.x()) / ;

         QPointF startPt = myStartItem->pos();

         QPointF endPt = myEndItem->pos();

         endPt.setX(midX);

         endPt.setY(startPt.y());

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt.setX(startPt.x());

         endPt.setY(myEndItem->pos().y());

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt = myEndItem->pos();

         DrawArrow(painter, startPt, endPt, true);

     }

 }

 void Arrow::TwoLine(QPainter *painter, QPointF startPt, QPointF endPt)

 {

     if(m_lineType == LineType::lineType2){

         endPt.setX(startPt.x());

         endPt.setY(endPt.y());

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt = myEndItem->pos();

         DrawArrow(painter, startPt, endPt, true);

     }

     else if(m_lineType == LineType::lineType1){

         endPt.setY(startPt.y());

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt = myEndItem->pos();

         DrawArrow(painter, startPt, endPt, true);

     }

 }

 //void Arrow::SetLineStyle(bool bVhvLine)

 //{

 //    m_bVhvLine = bVhvLine;

 //}

 void Arrow::SetLineType(LineType lineType)

 {

     if(lineType > lineType4 || lineType < lineType1)

         m_lineType = lineType1;

     else{

         m_lineType = lineType;

     }

 }

 void Arrow::DrawLine(QPainter *painter, QPointF start, QPointF end)

 {

     if(m_lineType == LineType::lineType4){

         qreal midY = (start.y() + end.y()) / ;

         QPointF startPt = myStartItem->pos();

         QPointF endPt = myEndItem->pos();

         endPt.setX(startPt.x());

         endPt.setY(midY);

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt.setX(myEndItem->pos().x());

         endPt.setY(startPt.y());

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt = myEndItem->pos();

         DrawArrow(painter, startPt, endPt, true);

     }

     else if(m_lineType == LineType::lineType3){

         qreal midX = (start.x() + end.x()) / ;

         QPointF startPt = myStartItem->pos();

         QPointF endPt = myEndItem->pos();

         endPt.setX(midX);

         endPt.setY(startPt.y());

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt.setX(startPt.x());

         endPt.setY(myEndItem->pos().y());

         DrawArrow(painter, startPt, endPt, false);

         startPt = endPt;

         endPt = myEndItem->pos();

         DrawArrow(painter, startPt, endPt, true);

     }

     else if(m_lineType == LineType::lineType2){

         end.setX(start.x());

         end.setY(end.y());

         DrawArrow(painter, start, end, false);

         start = end;

         end = myEndItem->pos();

         DrawArrow(painter, start, end, true);

     }

     else if(m_lineType == LineType::lineType1){

         end.setY(start.y());

         DrawArrow(painter, start, end, false);

         start = end;

         end = myEndItem->pos();

         DrawArrow(painter, start, end, true);

     }

     else {//默认是linetype1

         m_lineType = LineType::lineType1;

         end.setY(start.y());

         DrawArrow(painter, start, end, false);

         start = end;

         end = myEndItem->pos();

         DrawArrow(painter, start, end, true);

     }

 }

这个类中，有一些代码冗余。

我在这里分了四类画线方式，即头文件中的LineType。在横竖横和竖横竖的类型中，中间线段取的是中点画线。箭头首尾的节点都有了，保存也可以的。也可以根据个人情况修改箭头类。

操作：编辑图形时，基本图形时拖拽到场景中的。连线不是拖拽，是单击选中一种类型，在场景中连接两个基本图形即可。选中一个画线方式，再次拖拽基本图形或右键鼠标后，需要再次选择画线方式，才能再次画线。右键鼠标会出现右键菜单，打开、保存、删除。保存，保存场景中图形为xml；打开，打开保存的xml文件；删除，可删除基本图形或者箭头。注意：删除基本图形时，如果基本图形有连线，连线也会被删除。

还有一些功能待完善，如修改基本图形的名称等。

结果图：

稍后把代码传到csdn。如果博客园能上传代码就好了。

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