qt鼠标事件总结（坐标，跟踪，点击判断）

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
class MouseEvent : public QMainWindow
{ Q_OBJECT
public:MouseEvent();
~MouseEvent();
private:
QLabel *labelStatus;
QLabel *labelMousePos;
protected :
void mouseMoveEvent ( QMouseEvent * e );
void mousePressEvent ( QMouseEvent * e );
void mouseReleaseEvent ( QMouseEvent * e );
void mouseDoubleClickEvent( QMouseEvent * e );
};

#endif

//main.cpp

#include

#include "mouseevent.h"
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
MouseEvent w;w.show();
return app.exec();
}

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