键盘事件：
在图像处理和游戏应用程序中，有时需要通过键盘控制某个对象的移动，此功能可以 通过
对键盘事件的处理来实现。键盘事件的获取是通过重定义QWIDGET类的KEYPressEvent()
和KEYRELEASEEVENT()来实现的。
通过键盘的上、下、左、右方向键可以控制图标的移动，移动的步进值 为风格的大小，如果
同时按下CTRL键，则实现细微移动；若按下HOME键，则光标回到界面的左上顶点；若按下
END键，则光标到达界面的右下顶点。
具体实现步骤如下
（1）头文件keyevent.h 的具体内容如下：
#ifndef KEYEVENT_H
#define KEYEVENT_H#include <QWidget>
#include <QKeyEvent>
#include <QPaintEvent>class KeyEvent : public QWidget
{Q_OBJECTpublic:KeyEvent(QWidget *parent = nullptr);~KeyEvent();void drawPix();void keyPressEvent(QKeyEvent *event) ;void paintEvent(QPaintEvent *event) ;
private:QPixmap *pix;QImage image;int startX;int startY;int width;int height;int step;
};
#endif // KEYEVENT_H
（2）源文件keyevent.cpp的具体代码内容如下：
#include "keyevent.h"
#include <QPainter>KeyEvent::KeyEvent(QWidget *parent): QWidget(parent)
{setWindowTitle(tr("键盘事件"));setAutoFillBackground(true);QPalette palette = this->palette();palette.setColor(QPalette::Window,Qt::white);setPalette(palette);setMinimumSize(512,256);setMaximumSize(512,256);width =size().width();height=size().height();pix=new QPixmap(width,height);pix->fill(Qt::white);image.load("../image/image.png"); // ../ :表示EXE程序的上级目录。 ./:表示exe程序的同级目录startX=100;startY=100;step = 20;drawPix();resize(512,256);
}KeyEvent::~KeyEvent()
{
}void KeyEvent::drawPix()
{pix->fill(Qt::white);QPainter *painter = new QPainter;QPen pen(Qt::DotLine);for(int i=step; i<width;i=i+step)// 按照步进值的间隔绘制纵向的网格线{painter->begin(pix);painter->setPen(pen);painter->drawLine(QPoint(i,0),QPoint(i,height));painter->end();}for(int j=step; j<width;j=j+step) // 按照步进值的间隔绘制横向的网格线{painter->begin(pix);painter->setPen(pen);painter->drawLine(QPoint(0,j),QPoint(width,j));painter->end();}painter->begin(pix);painter->drawImage(QPoint(startX,startY),image);painter->end();
}void KeyEvent::keyPressEvent(QKeyEvent *event)
{ // 按钮 ： CTRL + 方向键 的事件if(event->modifiers()==Qt::ControlModifier){if(event->key()==Qt::Key_Left){startX=(startX-1<0)?startX:startX-1;}if(event->key()==Qt::Key_Right){startX=(startX+1+image.width()>width)?startX:startX+1;}if(event->key()==Qt::Key_Up){startY=(startY-1<0)?startY:startY-1;}if(event->key()==Qt::Key_Down){startY=(startY+1+image.height()>height)?startY:startY+1;}}else{/* 首先调节图标左上顶点的位置至风格的顶点上*/startX= startX-startX%step;startY= startY-startY%step;if(event->key()==Qt::Key_Left){startX=(startX-step<0)?startX:startX-step;}if(event->key()==Qt::Key_Right){startX=(startX+step+image.width()>width)?startX:startX+step;}if(event->key()==Qt::Key_Up){startY=(startY-step<0)?startY:startY-step;}if(event->key()==Qt::Key_Down){startY=(startY+step+image.height()>height)?startY:startY+step;}if(event->key()==Qt::Key_Home){startX = 0;startY = 0;}if(event->key()==Qt::Key_End){startX= width-image.width();startY= height-image.height();}}drawPix();//根据调整后的图标位置重新在PIX中绘制图像update(); // 触发界面重画
}void KeyEvent::paintEvent(QPaintEvent *)
{QPainter painter;painter.begin(this);painter.drawPixmap(QPoint(0,0),*pix);painter.end();
}
（3）在项目工程所在目录（D:\QT\CH11\CH1102\KeyEvent）下新建一个文件夹并命名为image,在文件夹内保存一个名为“image.png”的图片；在项目中按照以下步骤添加资源文件。
（A）在项目名“KeyEvent”上单击鼠标右键->"添加新文件..."菜单项，在如图11.3所示的对话框中单击“Qt”模板->"Qt Resource File" ->"Choose..."按钮。
（B）在弹出的对话框中选择资源要存放的路径，如图11.4所示在“名称” 栏中填写资源名称“keyevent”。单击“下一步”按钮，单击“完成”按钮。此时，项目下自动添加一个"keyevent.qrc "资源文件，如图11.5所示。
图11.5 添加后的项目目录树
（C）、鼠标右击资源文件，选择“add Prefix...”菜单项，在弹出的“Add Prefix”对话框的“Prefix:”
栏中填写“/new/prifix1”,单击"oK"按钮，此时项目目录树右区资源文件下新增了一个“/new/prefix1”子目录项，单击该区下方“添加”按钮上的 "添加文件',按照如图11.6所示的步骤操作，在弹出的对话框中选项“image/image.png”文件，单击“提示”按钮，将该图片添加到项目中。
（4）drawPix()函数实现了在QPixmap对象上绘制图像，其具体代码如下：
void KeyEvent::drawPix()
{pix->fill(Qt::white);QPainter *painter = new QPainter;QPen pen(Qt::DotLine);for(int i=step; i<width;i=i+step)// 按照步进值的间隔绘制纵向的网格线{painter->begin(pix);painter->setPen(pen);painter->drawLine(QPoint(i,0),QPoint(i,height));painter->end();}for(int j=step; j<width;j=j+step) // 按照步进值的间隔绘制横向的网格线{painter->begin(pix);painter->setPen(pen);painter->drawLine(QPoint(0,j),QPoint(width,j));painter->end();}painter->begin(pix);painter->drawImage(QPoint(startX,startY),image);painter->end();
}
（5）keyPressEvent()函数处理键盘的按下事件，具体代码如下：
void KeyEvent::keyPressEvent(QKeyEvent *event)
{ // 按钮 ： CTRL + 方向键 的事件if(event->modifiers()==Qt::ControlModifier){if(event->key()==Qt::Key_Left){startX=(startX-1<0)?startX:startX-1;}if(event->key()==Qt::Key_Right){startX=(startX+1+image.width()>width)?startX:startX+1;}if(event->key()==Qt::Key_Up){startY=(startY-1<0)?startY:startY-1;}if(event->key()==Qt::Key_Down){startY=(startY+1+image.height()>height)?startY:startY+1;}}else{/* 首先调节图标左上顶点的位置至风格的顶点上*/startX= startX-startX%step;startY= startY-startY%step;if(event->key()==Qt::Key_Left){startX=(startX-step<0)?startX:startX-step;}if(event->key()==Qt::Key_Right){startX=(startX+step+image.width()>width)?startX:startX+step;}if(event->key()==Qt::Key_Up){startY=(startY-step<0)?startY:startY-step;}if(event->key()==Qt::Key_Down){startY=(startY+step+image.height()>height)?startY:startY+step;}if(event->key()==Qt::Key_Home){startX = 0;startY = 0;}if(event->key()==Qt::Key_End){startX= width-image.width();startY= height-image.height();}}drawPix();//根据调整后的图标位置重新在PIX中绘制图像update(); // 触发界面重画
}
（6）界面重绘函数paintEvent()，将pix绘制在界面上。其具体代码如下：
void KeyEvent::paintEvent(QPaintEvent *)
{QPainter painter;painter.begin(this);painter.drawPixmap(QPoint(0,0),*pix);painter.end();
}
（7）项目KEYEVENT.PRO 详细代码
QT += core guigreaterThan(QT_MAJOR_VERSION, 4): QT += widgetsCONFIG += c++11# The following define makes your compiler emit warnings if you use
# any Qt feature that has been marked deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS# You can also make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0SOURCES += \main.cpp \keyevent.cppHEADERS += \keyevent.hTRANSLATIONS += \KeyEvent_zh_CN.ts# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += targetRESOURCES += \keyevent.qrc
（8）运行结果如图11.2所示。