Qt使用Poppler实现pdf阅读器的示例代码

开发环境 Qt5.5.1、Qt Creator 3.5.1

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Qt实现pdf阅读器和MFC实现pdf阅读器，其实原理都是差不多的。

需要用到Poppler开源库，下载地址如下 https://poppler.freedesktop.org/

如果只是要在window的gcc下运行的话，可以下载已经编译好的库 https://sourceforge.net/projects/poppler-win32/

Qt 使用Poppler实现pdf阅读器的示例代码

注意：这个是MinGW版本的Qt，也就是运行在GCC环境下的库，里面只包含 *.dll 和 *.a 。如果是Vistual Studio版本的Qt ，那么很不幸里面没有 *.lib文件。

1、新建项目，在项目的根目录新建一个“poppler”文件夹，将poppler中qt5目录下的文件都丢进去（*.h头文件，另外再将编译好的2个*.a文件和2个*.dll丢进去，我这里多丢了实现的*.cc文件，因为*.cc已经被编译成动态库了，所以可以不用包含在代码中）

Qt 使用Poppler实现pdf阅读器的示例代码

2、在项目的pro配置文件中添加以下内容，引用poppler的头文件和库文件（注意：我这里是win32，所以前面加了win32前缀）

INCLUDEPATH += $$PWD/poppler
win32: LIBS += -L$$PWD/poppler -llibpoppler
win32: LIBS += -L$$PWD/poppler -llibpoppler-qt5

3、创建pdf工具类（该类负责与poppler库做对接，主要负责获取pdf的总页数，和每页的图像）

（1）pdfutils.h

#ifndef PDFUTILS_H
#define PDFUTILS_H
#include <QObject>
#include <QImage>
#include <QSize>
#include <QDebug>
#include "poppler-qt5.h"
class PdfUtils
{
public:
  explicit PdfUtils(QString filePath);
  ~PdfUtils();
  //获取指定页pdf图像(页码从0开始)
  QImage getPdfImage(int pageNumber);
  //获取pdf总页码
  int getNumPages();
  //获取pdf页面大小
  QSize getPageSize();
private:
  QString filePath;
  int numPages;
  QSize pageSize;
  void getPdfInfo();
};
#endif // PDFUTILS_H

（2）pdfutils.cpp

#include "pdfutils.h"
PdfUtils::PdfUtils(QString filePath) {
  this->filePath = filePath;
  getPdfInfo();
}
PdfUtils::~PdfUtils() {
}
QImage PdfUtils::getPdfImage(int pageNumber) {
  QImage image;
  Poppler::Document* document = Poppler::Document::load(filePath);
  if (!document || document->isLocked()) {
    // ... error message ....
    delete document;
    return image;
  }
  // Document starts at page 0
  Poppler::Page* pdfPage = document->page(pageNumber);
  if (pdfPage == 0) {
    // ... error message ...
    return image;
  }
  // Generate a QImage of the rendered page
  image = pdfPage->renderToImage(72, 72, -1, -1, -1, -1);
  if (image.isNull()) {
    // ... error message ...
    return image;
  }
  // after the usage, the page must be deleted
  delete pdfPage;
  delete document;
  return image;
}
int PdfUtils::getNumPages() {
  return numPages;
}
QSize PdfUtils::getPageSize() {
  return pageSize;
}
void PdfUtils::getPdfInfo() {
  numPages = 0;
  Poppler::Document* document = Poppler::Document::load(filePath);
  if (!document || document->isLocked()) {
    // ... error message ....
    delete document;
    return;
  }
  numPages = document->numPages();
  Poppler::Page* pdfPage = document->page(0);
  pageSize = pdfPage->pageSize();
  qDebug()<<pageSize;
  delete pdfPage;
  delete document;
}

4、pdf显示类（pdf的右侧显示滚动条，①拖动滚动条翻页 ②鼠标拖动pdf到最上或最底时翻页）

注意：本文省略了页面缓存，如果是真实的项目的话，本着严谨的态度，请务必缓存页面

（1）mypdfcanvas.h（继承父类的resizeEvent是为了 ①当pdf只有1页时不显示滚动条 ②当用户拖动缩放窗口时动态改变pdf显示尺寸）

#ifndef MYPDFCANVAS_H
#define MYPDFCANVAS_H
#include <QWidget>
#include <QVector>
#include <QMouseEvent>
#include <QPaintEvent>
#include <QPainter>
#include <QPaintEvent>
#include <QMap>
#include <QPalette>
#include <QResizeEvent>
#include "pdfutils.h"
class MyPdfCanvas : public QWidget
{
  Q_OBJECT
public:
  explicit MyPdfCanvas(QWidget *parent = 0);
  ~MyPdfCanvas();
  void resizeEvent(QResizeEvent* e);
  void paintEvent(QPaintEvent *e);
  void mousePressEvent(QMouseEvent *e);
  void mouseReleaseEvent(QMouseEvent *e);
  void mouseMoveEvent(QMouseEvent *e);
  void setMaxCachedNum(int maxCachedNum);
  //如果不能解析pdf返回false
  bool setPath(QString pdfPath);
  //页码从0开始
  bool setPage(int pageNumber);
  //获取页数
  int getNumPages();
  float getScaledRatio();
  //显示裁剪后的图片
  bool showClipImage(int pageNumber, int x, int y, int w, int h);
  //取消显示裁剪图片,恢复正常显示
  void cancelClip();
  //实际获取的pdf宽高度
  QSize pdfActualSize;
signals:
  void pageChanged(int currentPage);
private:
  PdfUtils* pdfUtils;
  QString pdfPath;
  //最大缓存图片数量
  int maxCachedNum;
  //用来缓存pdf的每一个页面的图像(从0开始)
  QMap<int, QImage> cachedImageMap;
  //用来存储已缓存的pdf页面序号(从0开始)
//  QQueue<int> cachedPageQueue;
  //当前页码(从0开始)
  int currentPage;
  //总页码(从0开始)
  int numPages;
  bool isMouseDown;
  int lastMouseY;
  //当前pdf页面的图像
  QImage image;
  int imageX;
  int imageY;
  int imageMinY;
  //是否是剪裁状态
  bool isClip;
  //获取指定页的图片
  bool getPdfImage(int pageNumber);
  void reachTop();
  void reachBottom();
  //判断是否需要发送重定位签名框的信号
  void needLocateSignArea();
};
#endif // MYPDFCANVAS_H

（2）pdfcanvas.cpp

#include "mypdfcanvas.h"
MyPdfCanvas::MyPdfCanvas(QWidget *parent) : QWidget(parent) {
  pdfUtils = NULL;
  imageX = 0;
  imageY = 0;
  isClip = false;
  setAutoFillBackground(true);
}
MyPdfCanvas::~MyPdfCanvas() {
  if(pdfUtils != NULL) delete pdfUtils;
}
void MyPdfCanvas::resizeEvent(QResizeEvent *e) {
  image = this->cachedImageMap[currentPage];
  if(!image.isNull()) {
    float radio = (float)e->size().width()/(float)e->oldSize().width();
    int imageHeight = image.height()* e->size().width()/image.width();
    image = image.scaled(e->size().width(), imageHeight);
    if(imageHeight < this->height()) {
      imageY = (this->height()-imageHeight)/2;
      //如果图片高度小于控件高度，则图片居中
//      imageMinY = imageY;
      imageMinY = 0;
      imageY = imageMinY;
    } else {
      if(radio>0) {
        imageY = (int)(imageY*radio);
        if(imageY > 0) {
          imageY = 0;
        }
      } else {
        imageY = 0;
      }
    }
  }
}
void MyPdfCanvas::paintEvent(QPaintEvent *e) {
  QPainter* painter = new QPainter(this);
  if(image.isNull()) {
    painter->fillRect(this->rect(), Qt::transparent);
    return;
  }
  painter->drawImage(0, imageY, image);
  delete painter;
}
void MyPdfCanvas::mousePressEvent(QMouseEvent *e) {
  isMouseDown = true;
  lastMouseY = e->y();
}
void MyPdfCanvas::mouseReleaseEvent(QMouseEvent *e){
  isMouseDown = false;
}
void MyPdfCanvas::mouseMoveEvent(QMouseEvent *e){
  if(!isMouseDown || image.isNull()) {
    return;
  }
  int distance = e->y() - lastMouseY;
  lastMouseY = e->y();
  imageY += distance;
  if(imageY > 0) {
    imageY = 0;
    reachTop();
    return;
  } else if(imageY < imageMinY) {
    imageY = imageMinY;
    reachBottom();
    return;
  }
  update();
}
void MyPdfCanvas::setMaxCachedNum(int maxCachedNum) {
  this->maxCachedNum = maxCachedNum;
}
bool MyPdfCanvas::setPath(QString pdfPath) {
  this->pdfPath = pdfPath;
  if(pdfUtils != NULL) delete pdfUtils;
  pdfUtils = new PdfUtils(pdfPath);
  numPages = pdfUtils->getNumPages();
  if(numPages > 0) {
    isClip = false;
    pdfActualSize = pdfUtils->getPageSize();
  }
  cachedImageMap.clear();
  currentPage = 0;
  imageY = 0;
  lastMouseY = 0;
  return numPages > 0;
}
bool MyPdfCanvas::setPage(int pageNumber) {
  if(!getPdfImage(pageNumber)) {
    return false;
  }
  isClip = false;
  isMouseDown = false;
  image = image.scaledToWidth(this->width());
  imageMinY = this->height() - image.height();
  if(image.height() < this->height()) {
    //如果图片高度小于控件高度，则图片居中
//    imageMinY /= 2;
    imageMinY = 0;
    imageY = imageMinY;
  } else {
    imageY = 0;
  }
  update();
  return true;
}
int MyPdfCanvas::getNumPages() {
  return numPages;
}
float MyPdfCanvas::getScaledRatio() {
  int pdfWidth = pdfUtils->getPageSize().width();
  return (float)this->width()/(float)pdfWidth;
}
bool MyPdfCanvas::showClipImage(int pageNumber, int x, int y, int w, int h) {
  if(!getPdfImage(pageNumber)) {
    return false;
  }
  isClip = true;
  imageY = 0;
  image = image.copy(x, y, w, h).scaled(this->size());
  update();
}
void MyPdfCanvas::cancelClip() {
  isClip = false;
  setPage(currentPage);
}
bool MyPdfCanvas::getPdfImage(int pageNumber) {
  if(pageNumber<0 || pageNumber >= numPages) {
    return false;
  }
  if(cachedImageMap.contains(pageNumber)) {
    image = cachedImageMap.value(pageNumber);
  } else {
    image = pdfUtils->getPdfImage(pageNumber);
    if(!image.isNull()) {
      cachedImageMap[pageNumber] = image;
      pdfActualSize = image.size();
    }
  }
  if(image.isNull()) {
    return false;
  }
  currentPage = pageNumber;
  return true;
}
void MyPdfCanvas::reachTop() {
  if(currentPage > 0) {
    emit pageChanged(currentPage-1);
  }
}
void MyPdfCanvas::reachBottom() {
  if(currentPage < numPages-1) {
    emit pageChanged(currentPage+1);
  }
}

5、pdf及右侧滑块的装载容器

（1）mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QScrollBar>
#include "mypdfcanvas.h"
#define SCROLLBAR_WIDTH 30
class MainWindow : public QMainWindow
{
  Q_OBJECT
public:
  explicit MainWindow(QWidget *parent = 0);
  ~MainWindow();
  void resizeEvent(QResizeEvent* e);
  bool setPdfPath(QString path);
  //重新调整pdf界面大小
  void resizeCanvas();
  void setWidgetVisible(bool pdfCanvasVisible, bool scrollbarVisible);
public slots:
  //当拖动pdf上滑到顶（或下滑到底）时触发该方法
  onPageChange(int currentPage);
  //当滑动条的滑块被滑动时，会调用该方法
  onScrollBarValueChange();
private:
  MyPdfCanvas *pdfCanvas;
  QScrollBar *scrollbar;
};
#endif // MAINWINDOW_H

（2）mainwindow.cpp

#include "mainwindow.h"
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) {
  pdfCanvas = new MyPdfCanvas(this);
  scrollbar = new QScrollBar(Qt::Vertical, this);
  setWidgetVisible(false, false);
  connect(pdfCanvas, SIGNAL(pageChanged(int)), this, SLOT(onPageChange(int)));
  connect(scrollbar, SIGNAL(valueChanged(int)), this, SLOT(onScrollBarValueChange()));
}
MainWindow::~MainWindow() {
}
void MainWindow::resizeEvent(QResizeEvent *e) {
  resizeCanvas();
}
bool MainWindow::setPdfPath(QString path) {
  bool result = pdfCanvas->setPath(path);
  if(result) {
    int numPages = pdfCanvas->getNumPages();
    if(numPages>1) {
      scrollbar->setMaximum(numPages-1);
      scrollbar->setValue(0);
    }
    pdfCanvas->setPage(0);
  }
  resizeCanvas();
  return result;
}
void MainWindow::resizeCanvas() {
  qDebug()<<"resize "<<this->rect()<<", "<<pdfCanvas->rect();
  int numPages = pdfCanvas->getNumPages();
  if(numPages == 1) {
    pdfCanvas->setGeometry(this->rect());
    setWidgetVisible(true, false);
  } else if(numPages > 1) {
    pdfCanvas->setGeometry(0, 0, this->width()-SCROLLBAR_WIDTH, this->height());
    scrollbar->setGeometry(this->width()-SCROLLBAR_WIDTH, 0, this->width()-SCROLLBAR_WIDTH, this->height());
    setWidgetVisible(true, true);
  } else {
    //numPages <= 0
    setWidgetVisible(false, false);
  }
}
void MainWindow::setWidgetVisible(bool pdfCanvasVisible, bool scrollbarVisible) {
  pdfCanvas->setVisible(pdfCanvasVisible);
  scrollbar->setVisible(scrollbarVisible);
}
MainWindow::onPageChange(int currentPage) {
  pdfCanvas->setPage(currentPage);
}
MainWindow::onScrollBarValueChange() {
  pdfCanvas->setPage(scrollbar->value());
}

6、调用方式

（1）main.cpp

#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  MainWindow w;
  w.resize(500, 500);
  w.show();
  QString path = "D://test.pdf";
  w.setPdfPath(path);
  w.setWindowTitle(path);
  return a.exec();
}

7、实际效果图

Qt 使用Poppler实现pdf阅读器的示例代码