本篇主要在qt做一个例子读取cad文件数据，使用的开源库是dxflib。用到dxflib的DL_CreationAdapter，DL_Dxf。DL_Dxf是用来读取.dxf文件的类，DL_CreatinAdapter是一个容器，当DL_Dxf加载.dxf文件后，就会响应DL_CreationAdapter这个类，读取cad数据。
我们来看看他的工作原理：

//自己声明一个类继承DL_CreationAdapter
class MyDxfFilter : public DL_CreationAdapter {
//重写虚函数来把度出来的数据保存到自己设计好的数据结构中
virtual void addLine(const DL_LineData& d);
...
}
void MyDxfFilter::addLine(const DL_LineData& d) {
std::cout
在这段程序中，当dxf.in("drawing.dxf", &f)读取.dxf文件成功了，如果文件中有很多line，那么f对象会一直递归调用虚函数接口addLine()，直到所有的line都读完。
重这个特征，我们就可以把所有我们要读取的数据都出来了！
直接上程序！：
entitiesDatas.h

ifndef ENTITIESDATAS_H

define ENTITIESDATAS_H

include

include "dl_dxf.h"

include "dl_creationadapter.h"

include "dl_attributes.h"

include "dl_codes.h"

include "dl_entities.h"

include "dl_exception.h"

include "dl_global.h"

include "dl_writer.h"

include "dl_writer_ascii.h"

include

include

class EntitiesDatas:public DL_CreationAdapter
{
public:
// explicit EntitiesDatas();

virtual void EntitiesDatas::addPoint(const DL_PointData &d){    points.append(d);    qDebug()>>>>>>>>>>>>>>>>>>>>>>>>>>>>add xdata string";}virtual void EntitiesDatas::addXRecord(const std::string &){    qDebug()getAttributes().getColor();}virtual void EntitiesDatas::endSequence(){    qDebug()getAttributes().getColor()==1){        QString color="# ef3312";        hatchcolors.append(color);    }    else if(this->getAttributes().getColor()==2){        QString color="# efef33";        hatchcolors.append(color);    }    else if(this->getAttributes().getColor()==3){        QString color="# 12ef33";        hatchcolors.append(color);    }    else {        QString color="# efefef";        hatchcolors.append(color);    }}

// virtual void EntitiesDatas::att

QList points;QList lines;//QList arcs;QList circles;//QList ellipses;QList texts;QList dimangulars;QList dimlines;QList radias;QList vertices;//QList polylines;//QList mtexts;//QList hatches;//QList hatchedges;//QList hatchcolors;

};

endif // ENTITIESDATAS_H

dxfreader.h

ifndef DXFREADER_H

define DXFREADER_H

include

include "entitiesdatas.h"

include "dl_dxf.h"

include "dl_creationadapter.h"

include "dl_attributes.h"

include "dl_codes.h"

include "dl_entities.h"

include "dl_exception.h"

include "dl_global.h"

include "dl_writer.h"

include "dl_writer_ascii.h"

include

include "entitiesdatas.h"

include

class DXFReader : public QObject
{
Q_OBJECT
public:
explicit DXFReader(QObject *parent = 0);

//lineQ_INVOKABLE int getLineLength();Q_INVOKABLE double getLinex1(int index);Q_INVOKABLE double getLinex2(int index);Q_INVOKABLE double getLiney1(int index);Q_INVOKABLE double getLiney2(int index);//circleQ_INVOKABLE int getCircleLength();Q_INVOKABLE double getCirclex(int index);Q_INVOKABLE double getCircley(int index);Q_INVOKABLE double getCircleRadius(int index);//mtextQ_INVOKABLE int getMTextLength();Q_INVOKABLE double getMTextx(int index);Q_INVOKABLE double getMTexty(int index);Q_INVOKABLE QString getMTextStr(int index);Q_INVOKABLE double getMTextSize(int index);//ploy lineQ_INVOKABLE int getPolyLineLength();Q_INVOKABLE double getVertex1x(int index);Q_INVOKABLE double getVertex2x(int index);Q_INVOKABLE double getVertex3x(int index);Q_INVOKABLE double getVertex4x(int index);Q_INVOKABLE double getVertex1y(int index);Q_INVOKABLE double getVertex2y(int index);Q_INVOKABLE double getVertex3y(int index);Q_INVOKABLE double getVertex4y(int index);//hatch edge and hatch colorQ_INVOKABLE int getHatchLength();Q_INVOKABLE QString getHatchColor(int index);Q_INVOKABLE double getHatchx(int index);Q_INVOKABLE double getHatchy(int index);Q_INVOKABLE double getHatchRadius(int index);

signals:

public slots:
private:
EntitiesDatas f;
DL_Dxf dxf;
};

endif // DXFREADER_H

dxfreader.cpp

include "dxfreader.h"

include "math.h"

include "QtMath"

DXFReader::DXFReader(QObject *parent) : QObject(parent)
{
//初始化第一个dxf文件
if (!dxf.in("c:/aa.dxf", &f)) {
qDebug()
上面程序我是设计成暴露给qml使用的数据，一边使用qml中的canvas来绘制cad数据
看看都出来的数据效果图:

到这里，这个实现方法有个缺点，就是使用了qml 中的canvas绘制数据，当把canvas进行缩放的时候，onpaint事件被响应，但是数据很多，所以缩放越大，消耗内存就越大，搞得有点卡顿，不过这方法的有点就是方便，省了很多时间。
关于dxflib的搭建，很简单，只需要在qcad官网下载dxflib源码，用qt编译出dxflib.lib文件，然后用自己喜欢的方式放到指定目录，就可以使用了。

关键字：cad, qt, qml, #c++#

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