三个水平的坐标系,如图

首先说明，本案列是直接继承QCustomPlot,如果是需要通过非继承方式，自行将其中的this关键字替换为QCustomPlot* X 的X；文中有些代码省略了this，自行判断。
一、添加多个坐标系
步骤如下：

//! 1.清空布局中默认的坐标系及其他控件
this->plotLayout()->clear();/*  在.h文件中定义好的需要使用的控件
QCPAxisRect * A0_5;			//坐标系 1
QCPAxisRect * A0_50;		//坐标系 2
QCPAxisRect * V0_150;		//坐标系 3
QCPItemTracer* tracer;		//游标
QCPItemText* tracerLabel;	//游标标签
*/
V0_150 = nullptr;
A0_50 = nullptr;
A0_5 = nullptr;
legend = nullptr;
tracer = nullptr;
tracerLabel = nullptr;//! 2.创建游标及游标标签  
tracer_init();
/* 创建代码就在此处注释中描述，实际使用中写在对应方法中if(tracer == nullptr){tracer = new QCPItemTracer(this);tracer->setInterpolating(false);//禁用插值tracer->setPen(QPen(QBrush(QColor(Qt::red)),Qt::DashLine));//虚线游标tracer->setStyle(QCPItemTracer::tsCrosshair);//游标样式：十字星、圆圈、方框tracerLabel = new QCPItemText(this);tracerLabel->setLayer("overlay");tracerLabel->setPen(QPen(Qt::black));tracerLabel->setBrush(Qt::cyan);tracerLabel->setPadding(QMargins(2,2,2,2));//边界宽度tracerLabel->setPositionAlignment(Qt::AlignLeft | Qt::AlignTop);// 标签显示位置，左上tracerLabel->position->setParentAnchor(tracer->position); // 标签跟随游标}
*///! 3. 添加坐标系  三个坐标系的创建、样式属性分别在不同方法进行，方便维护
V0_150_init();
A0_50_init();
A0_5_init();
/* 坐标系的创建过程就不多余的描述，以注释中代码为例// 以智能指针方式定义dateTickerQSharedPointer<QCPAxisTickerDateTime> dateTicker(new QCPAxisTickerDateTime); dateTicker->setDateTimeFormat("yyyy-MM-dd\nhh:mm:ss"); // 设置以时间为X轴单位V0_150 = new QCPAxisRect(this, true);	// 创建坐标系V0_150->axis(QCPAxis::atBottom)->setTicker(dateTicker); // 将时间轴设置在坐标系中V0_150->axis(QCPAxis::atLeft)->setRange(0,150);	// 设置Y轴范围V0_150->setupFullAxesBox(true);    // 让四个轴关联，并全部显示出来V0_150->setRangeDrag(Qt::Horizontal | Qt::Vertical); //水平方向拖动 | 垂直方向移动V0_150->setRangeZoom(Qt::Horizontal | Qt::Vertical); //水平方向缩放 | 垂直方向缩放//如果是固定坐标系数量，可直接将坐标系添加如布局，\ 此处是动态添加和删除坐标系，所有魏加入布局//this->plotLayout()->addElement(axisRectCount(),0,V0_150); //axisRectCount()获取布局中坐标系个数
//! 4. legend
/*  if(legend == nullptr){legend = new QCPLegend;legend->setVisible(true);
//        plotLayout()->addElement(legend); //加入布局 
//! 注释:此处未加入布局和设置拉伸比的原因如下：由于初始第一个坐标系和legend中都没有数据，legend高度会在布局中影响坐标系的高度。
所有在添加图层前将legend加入布局即可（如果有方法解决这个问题，可直接添加如布局）
//        plotLayout()->setColumnStretchFactor(1, 0.001); //设置行拉伸比例，将legend的宽度最小化connect(this, SIGNAL(selectionChangedByUser()), this, SLOT(when_selectionChangedByUser()));connect(this, SIGNAL(legendDoubleClick(QCPLegend*, QCPAbstractLegendItem*, QMouseEvent*)), this, SLOT(when_legendDoubleClick(QCPLegend*, QCPAbstractLegendItem*, QMouseEvent*)));}
*///! 5. 坐标系某些轴的隐藏
//axis_style_init(); //每添加或删除一个坐标系 或 同时添加或删除多个坐标系 调用一次
*/

//! MyCustomPlot::QCustomPlot
//! 以3个坐标系为例
void MyCustomPlot::axis_style_init()
{int index = 0;if(axisRectCount() == 2){foreach (auto *rect, axisRects()){index++;if(index == 1){rect->axis(QCPAxis::atTop)->setVisible(true);rect->axis(QCPAxis::atBottom)->setVisible(false);}else if(index == 2){rect->axis(QCPAxis::atTop)->setVisible(false);rect->axis(QCPAxis::atBottom)->setVisible(true);}}}else if(axisRectCount() == 3){foreach (auto *rect, axisRects()){index++;if(index == 1){rect->axis(QCPAxis::atTop)->setVisible(true);rect->axis(QCPAxis::atBottom)->setVisible(false);}else if(index == 2){rect->axis(QCPAxis::atTop)->setVisible(false);rect->axis(QCPAxis::atBottom)->setVisible(false);}else if(index == 3){rect->axis(QCPAxis::atTop)->setVisible(false);}}}
}

void MyCustomPlot::add_axis(int index) // 0 1 3 分别区别三个坐标系
{if(axisRectCount() >= 3) return;switch (index) {case 0:if(V0_150 == nullptr){	//若为空指针，调用函数V0_150_init();if(A0_50 != nullptr) //若不为空指针，建立信号槽，同步X轴，注意建立双向连接{connect(V0_150->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), A0_50->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));connect(A0_50->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), V0_150->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));}if(A0_5 != nullptr)	// 同理{connect(V0_150->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), A0_5->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));connect(A0_5->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), V0_150->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));}}plotLayout()->addElement(axisRectCount(),0,V0_150); // 将坐标系加入布局break;case 1:if(A0_50 == nullptr){A0_50_init();if(V0_150 != nullptr){connect(A0_50->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), V0_150->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));connect(V0_150->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), A0_50->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));}if(A0_5 != nullptr){connect(A0_50->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), A0_5->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));connect(A0_5->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), A0_50->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));}}plotLayout()->addElement(axisRectCount(),0,A0_50);break;case 2:if(A0_5 == nullptr){A0_5_init();if(A0_50 != nullptr){connect(A0_5->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), A0_50->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));connect(A0_50->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), A0_5->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));}if(V0_150 != nullptr){connect(A0_5->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), V0_150->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));connect(V0_150->axis(QCPAxis::atBottom), SIGNAL(rangeChanged(QCPRange)), A0_50->axis(QCPAxis::atBottom), SLOT(setRange(QCPRange)));}}plotLayout()->addElement(axisRectCount(),0,A0_5);break;default:break;}legend_init(); // 创建legend，根据自己需要创建axis_style_init();// 调整坐标系样式plotLayout()->simplify(); //简化布局replot(QCustomPlot::rpQueuedReplot); //刷新
}

void MyCustomPlot::delete_axis(int index)
{if(axisRectCount() <= 0) return;//axisRectCount()布局中坐标系数量switch (index) {case 0:if(V0_150 == nullptr) return;clearDataAndDeleteGraph(0);                 // 1. 清除数据，移除图层 不清除数据和图层，legend会保留信息，在legend点击事件发送时会程序崩溃plotLayout()->remove(axisRect(index));      // 2. 从布局中删除坐标系  并 deleteplotLayout()->simplify();                   // 3. 简化布局 // 2.3步骤是从布局中删除坐标系的关键，可自行测试无某一步骤造成的影响V0_150 = nullptr;  //避免成为野指针break;case 1:if(A0_50 == nullptr) return;clearDataAndDeleteGraph(1);plotLayout()->remove(axisRect(index));plotLayout()->simplify();A0_50 = nullptr;break;case 2:if(A0_5 == nullptr) return;clearDataAndDeleteGraph(2);plotLayout()->remove(axisRect(index));plotLayout()->simplify();A0_5 = nullptr;break;default:break;}if(axisRectCount() <= 0 && legend != nullptr) // customplot中无坐标系,删除legend{plotLayout()->remove(legend);plotLayout()->simplify();legend = nullptr;}else if(axisRectCount() > 0 && legend != nullptr){plotLayout()->take(legend);plotLayout()->simplify();plotLayout()->addElement(legend);plotLayout()->setColumnStretchFactor(1, 0.001);}axis_style_init();replot(QCustomPlot::rpQueuedReplot);
}

void MyCustomPlot::clearDataAndDeleteGraph(int index)
{	//! graph_Map保存了每一个图层指针graph_Map的key为 坐标系的type*10+idx, type就等于此函数中的index//void MyCustomPlot::addData(int idx, double key, double value, int type)for(QMap<int,QCPGraph*>::Iterator it = graph_Map.begin(); it != graph_Map.end(); it++){if(it.key()/10 == index){if(it.value() != nullptr){QCPGraph* graph = it.value();graph->data().data()->clear(); //清除数据graph_Map.remove(it.key()); //在移除MapremoveGraph(graph); //移除图层，不要自己delete,调用此函数自动deletereplot(QCustomPlot::rpQueuedReplot);}}}
}

// 判断数据加入的坐标系
void MyCustomPlot::addData(int idx, double key, double value, int type)
{if(!plotLayout()->hasElement(0,1) && legend != nullptr) // 将legend加入布局，一样的道理，自己选中合适的位置加入{plotLayout()->addElement(legend);plotLayout()->setColumnStretchFactor(1, 0.001);}switch (type) {case 0:if(V0_150 == nullptr) return;addData(idx+type*10, key, value, V0_150);break;case 1:if(A0_50 == nullptr) return;addData(idx+type*10, key, value, A0_50);break;case 2:if(A0_5 == nullptr) return;addData(idx+type*10, key, value, A0_5);break;default:break;}
}void MyCustomPlot::addData(int idx, double key, double value,QCPAxisRect* rect)
{QCPGraph* _graph;if(!graph_Map.contains(idx)) // 判断当前数据是否已有图层{	//创建图层并加入Mapgraph_Map.insert(idx, addGraph(rect->axis(QCPAxis::atBottom),rect->axis(QCPAxis::atLeft)));_graph = graph_Map.value(idx);_graph->setLineStyle(QCPGraph::lsStepLeft);        //设置连线类型_graph->setPen(QPen(QColor(qrand()%256, qrand()%256, qrand()%256),1)); //随机曲线颜色，qsrand(QTime(0,0,0).secsTo(QTime::currentTime())); 提前添加_graph->setScatterStyle(QCPScatterStyle(QCPScatterStyle::ssDisc, 3));        //显示散点数据_graph->addData(key, value); //添加数据if(!isMove){rect->axis(QCPAxis::atBottom)->setRange(key-1,key+1);rect->axis(QCPAxis::atLeft)->setRange(value-1,value+1);}LengedName_Map.insert(idx,QString("Curver%1").arg(idx));_graph->setName(LengedName_Map.value(idx));XRange = rect->axis(QCPAxis::atBottom)->range();YRange = rect->axis(QCPAxis::atLeft)->range();}else{_graph = graph_Map.value(idx);_graph->addData(key, value);if(!isMove){rect->axis(QCPAxis::atBottom)->setRange(key-1,key+1);rect->axis(QCPAxis::atLeft)->setRange( value-1 < rect->axis(QCPAxis::atLeft)->range().lower ? value-1 : rect->axis(QCPAxis::atLeft)->range().lower, value+1 > rect->axis(QCPAxis::atLeft)->range().upper ? value+1 : rect->axis(QCPAxis::atLeft)->range().upper);}_graph->setName(QString("%1  %2").arg(LengedName_Map.value(idx)).arg(value));}replot(QCustomPlot::rpQueuedReplot);                 //刷新图表
}

void MyCustomPlot::mousePressEvent(QMouseEvent *event)
{QCustomPlot::mousePressEvent(event);isMove = true;}void MyCustomPlot::mouseMoveEvent(QMouseEvent *event)
{QCustomPlot::mouseMoveEvent(event);if(tracer == nullptr || tracerLabel == nullptr || axisRectCount() <= 0 || tracer->graph() == nullptr) return;if(tracer->visible()){if(tracerGraph){QCPAxisRect* rect = nullptr;int key = graph_Map.key(tracerGraph,-1);if(key == -1) return;else if(key/10 == 0){rect = V0_150;}else if(key/10 == 1){rect = A0_50;}else if(key/10 == 2){rect = A0_5;}elsereturn;double x = rect->axis(QCPAxis::atBottom)->pixelToCoord(event->pos().x());//像素坐标转plot坐标tracer->setGraphKey(x);tracer->updatePosition(); //使得刚设置游标的横纵坐标位置生效double y = rect->axis(QCPAxis::atLeft)->pixelToCoord(event->pos().y());QString xTime = QDateTime::fromMSecsSinceEpoch(x * 1000.0).toString("hh:mm:ss.zzz");tracerLabel->setText(QString("x = %1\ny=%2").arg(xTime).arg(y));replot(QCustomPlot::rpQueuedReplot);}}
}void MyCustomPlot::mouseReleaseEvent(QMouseEvent *event)
{QCustomPlot::mouseReleaseEvent(event);isMove = false;
}void MyCustomPlot::when_selectionChangedByUser()
{for (QMap<int,QCPGraph*>::iterator it = graph_Map.begin(); it != graph_Map.end();it++){QCPGraph *graph = it.value();if(graph == nullptr) return;QCPPlottableLegendItem *item = legend->itemWithPlottable(graph);if (item->selected() || graph->selected())//选中了哪条曲线或者曲线的图例{tracerGraph = graph;if(tracer != nullptr){tracer->setGraph(tracerGraph);}item->setSelected(true);QPen pen;pen.setWidth(3);pen.setColor(Qt::blue);graph->selectionDecorator()->setPen(pen);graph->setSelection(QCPDataSelection(graph->data()->dataRange()));}}
}/*
双击图例修改曲线颜色
*/
void MyCustomPlot::when_legendDoubleClick (QCPLegend *legend, QCPAbstractLegendItem *legendItem, QMouseEvent *event)
{Q_UNUSED(legend);Q_UNUSED(event);qDebug()<<"when_legendDoubleClick (QCPLegend *legend, QCPAbstractLegendItem *legendItem, QMouseEvent *event)";for (int i = 0; i < this->graphCount(); ++i){QCPGraph *pGraph = this->graph(i);if(legendItem == this->legend->itemWithPlottable(pGraph))//查询被点击的图例项是哪个graph的图例项{QColor newColor = QColorDialog::getColor(Qt::red,this,"选择新颜色");if(newColor.isValid())//用户点击了确定{pGraph->setPen(QPen(newColor,1));replot(QCustomPlot::rpQueuedReplot);}}}
}