Qt鼠标事件总结

1、QMouseEvent中的坐标
QMouseEvent中保存了两个坐标，一个是全局坐标，当然另外一个是局部坐标。
全局坐标（globalPos（））即是桌面屏幕坐标(screen coordinates)，这个跟windows下的调用getCursorPos函数得到的结果一致。
局部坐标（pos（））即是相对当前active widget的坐标，左上角坐标为（0， 0）。

补充一个公式：
this->mapFromGlobal(this->cursor().pos()) = event.pos()

2、鼠标跟踪
在qt中，鼠标跟踪对应函数mouseMoveEvent。但是，默认情况下他并不能如期象你想象的那样响应鼠标的移动。此时，你只需在合适的位置调用一下函数setMouseTracking(true)即可。
If mouse tracking is switched off, mouse move events only occur if a mouse button is pressed while the mouse is being moved.
If mouse tracking is switched on, mouse move events occur even if no mouse button is pressed.
默认情况下，mouseMoveEvent响应你按下鼠标的某个键（拖动，但不局限于左键拖动）的鼠标移动。

3、鼠标左键拖动和左键点击的判断
鼠标左键点击很容易判断，一般就是在重写mousePressEvent函数，示例如下：
void XXXWidget::mousePressEvent(QMouseEvent *event)
{
if(event->button() == Qt::LeftButton)
{
       // todo ...
}
}
左键拖动的判断一般放在mouseMoveEvent函数中，但是你不能向上例一样来判断，因为该函数的event参数总是返回Qt::NoButton。你可以这样做：
void XXXWidget::mouseMoveEvent(QMouseEvent *event)
{
if(event->buttons() & Qt::LeftButton)
{
       // todo ...
}
}
参考教材实例，增加了注释和新功能，方便大家交流学习
// mouseevent.cpp
#include "mouseevent.h"
MouseEvent::MouseEvent( ):


QMainWindow()
{
    setWindowTitle(tr("Get Mouse Event"));
    setCursor(Qt::CrossCursor); //设置鼠标为十字星
    labelStatus = new QLabel();
    labelStatus->setMinimumSize(500,20);
    labelStatus->setFrameShape(QFrame::WinPanel);//设置标签形状
    labelStatus->setFrameShadow(QFrame::Sunken); //设置标签阴影;
    labelStatus->setText(tr("Mouse Position:"));
    labelStatus -> setFixedWidth (100);
    labelMousePos = new QLabel();
    labelMousePos->setText(tr(""));
    labelMousePos -> setFixedWidth (100);
    statusBar()->addPermanentWidget(labelStatus);//给状态栏添加永久的部件
    statusBar()->addPermanentWidget(labelMousePos);
    this->setMouseTracking ( true);//自动跟踪鼠标（默认情况下，mouseMoveEvent响应你按下鼠标的某个键的鼠标移动。）
  }
  
MouseEvent::~MouseEvent(){


}


void MouseEvent::mouseMoveEvent ( QMouseEvent * e )//鼠标移动事件响应
{    
    //1.获取局部鼠标位置
     labelMousePos ->setText("("+QString::number(e->x())+","+QString::number(e->y())+")");
    //2.获取全局鼠标位置
    QPoint coursePoint;
    coursePoint = QCursor::pos();//获取当前光标的位置
    labelMousePos ->setText("("+QString::number(coursePoint.x())+","+QString::number(coursePoint.y())+")");
}


void MouseEvent::mousePressEvent ( QMouseEvent * e )//鼠标单击事件响应
{
   QString str="("+QString::number(e->x())+","+QString::number(e->y())+")";
   if(e->button()==Qt::LeftButton){
      statusBar()->showMessage (tr("Mouse Left Button Pressed:")+str);//显示临时信息
   }
   else if(e->button()==Qt::RightButton){
                statusBar()->showMessage (tr("Mouse Right Button Pressed:")+str);
           }
          else if(e->button()==Qt::MidButton){
                       statusBar()->showMessage (tr("Mouse Middle Button Pressed:")+str);
         }
   }


void MouseEvent::mouseDoubleClickEvent( QMouseEvent * e )//鼠标双击事件响应
{       QString str="("+QString::number(e->x())+","+QString::number(e->y())+")";
         if(e->button()==Qt::LeftButton){
               statusBar()->showMessage (tr("Mouse Left Button Double Clicked:")+str);
          }
         else if(e->button()==Qt::RightButton){
                       statusBar()->showMessage (tr("Mouse Right Button Double Clicked:")+str);
                }
               else if(e->button()==Qt::MidButton){
                             statusBar()->showMessage (tr("Mouse Middle Button Double Clicked:")+str);
                      }
}


void MouseEvent::mouseReleaseEvent ( QMouseEvent * e )//鼠标松开事件响应
{
        QString str="("+QString::number(e->x())+","+QString::number(e->y())+")";
         statusBar()->showMessage (tr("Mouser Released:")+str,3000);
}


-------------//  mouseevent.h
#ifndef MOUSEEVENT_H
#define MOUSEEVENT_H


#include