17.QT-事件处理分析、事件过滤器、拖放事件

 void MainWindow::closeEvent(QCloseEvent *event)
{
     if (maybeSave())                        //如果还有需要保存的数据
    {
         writeSettings();
         event->accept();
    } 
     else                                    //取消关闭窗口
    {
         event->ignore();
    }
 }

void  accept ();    //接收者处理当前事件

void  ignore ();    //接收者忽略当前事件,忽略后,事件可能传递给父组件

bool isAccepted();  //判断当前事件是否被处理过 

#ifndef QMYLINEEDIT_H
#define QMYLINEEDIT_H

#include <QLineEdit>
#include <QtGui>

class QMyLineEdit : public QLineEdit
{
    Q_OBJECT

public:
    explicit QMyLineEdit(QWidget *parent = 0);

    void  keyReleaseEvent( QKeyEvent * event );
};

#endif // QMYLINEEDIT_H

#include "QMyLineEdit.h"

QMyLineEdit::QMyLineEdit(QWidget *parent) :
    QLineEdit(parent)
{

}

void  QMyLineEdit::keyReleaseEvent( QKeyEvent * event )
{
    qDebug()<<"QMyLineEdit::keyReleaseEvent";
    qDebug()<<"key value:"<< event->key();      
    event->ignore();                           //忽略当前事件
}

#ifndef QMYWIDGET_H
#define QMYWIDGET_H

#include "QMyLineEdit.h"
#include <QWidget>

class QMyWidget : public QWidget
{
    Q_OBJECT
    QMyLineEdit line;

public:
    explicit QMyWidget(QWidget *parent = 0);
    void   keyReleaseEvent( QKeyEvent * event );

};

#endif // QMYWIDGET_H

#include "QMyWidget.h"

QMyWidget::QMyWidget(QWidget *parent) :
    QWidget(parent),
    line(this)
{
}

void  QMyWidget::keyReleaseEvent( QKeyEvent * event )
{
    qDebug()<<"QMyWidget::keyReleaseEvent";
    qDebug()<<"key value:"<< event->key();

    QWidget::keyPressEvent(event);
}

int main(int argc, char *argv[])
{
        QApplication a(argc, argv);

        QMyWidget w;

        w.show();

        return a.exec();
}

bool QObject::eventFilter ( QObject * watched, QEvent * event );
       // watched:代表被监控的组件  event:代表要转发的事件
       //返回true,表示该事件也被过滤掉(处理),无需再转发了
       //返回false,则正常转发给watched

class MainWindow : public QMainWindow
 {
 public:
     MainWindow();

 protected:
     bool eventFilter(QObject *obj, QEvent *ev);

 private:
     QTextEdit *textEdit;
 };


 MainWindow::MainWindow()
 {
     textEdit = new QTextEdit;
     setCentralWidget(textEdit);
     textEdit->setAttribute(Qt::WA_InputMethodEnabled, false);     //禁止中文输入法
     textEdit->installEventFilter(this);
 }

 bool MainWindow::eventFilter(QObject *obj, QEvent *event)
 {
      if (obj == textEdit)
     {
         if (event->type() == QEvent::KeyPress)
         {
             QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
             qDebug() << "Ate key press" << keyEvent->key();
             switch(keyEvent->key())         //只接受0~9数字
             {
                case Qt::Key_0:
                case Qt::Key_1:
                case Qt::Key_2:
                case Qt::Key_3:
                case Qt::Key_4:
                case Qt::Key_5:
                case Qt::Key_6:
                case Qt::Key_7:
                case Qt::Key_8:
                case Qt::Key_9:
                    return false;
                default:
                    return true;
            }
         }
         else
         {
             return false;
         }
     }
     else
     {
       return QMainWindow::eventFilter(obj, event);
     }
 }

void  dragEnterEvent ( QDragEnterEvent * event );  //拖事件处理函数
void dropEvent ( QDropEvent * event ) ;           //放事件处理函数 

 class MainWindow : public QMainWindow
 {
private:
    QTextEdit *textEdit;
    void dragEnterEvent(QDragEnterEvent *event);
    void dropEvent(QDropEvent *event);

public:
    MainWindow();
 };

 MainWindow::MainWindow()
 {
     textEdit = new QTextEdit;
     setCentralWidget(textEdit);
     textEdit->setAttribute(Qt::WA_InputMethodEnabled, false) ;
     textEdit->installEventFilter(this);
     this->setAcceptDrops(true);
 }

void MainWindow::dragEnterEvent(QDragEnterEvent *event)
{
      if(event->mimeData()->hasUrls())      //判断拖的类型
      {
            event->acceptProposedAction();
      }
      else
      {
            event->ignore();
      }
}

void MainWindow::dropEvent(QDropEvent *event)
{
    if(event->mimeData()->hasUrls())        //判断放的类型
    {
        textEdit->clear();
        QList<QUrl> List = event->mimeData()->urls();

        for(int i=0;i<List.length();i++)
        {
            textEdit->insertPlainText(List[i].toLocalFile()+"\n");
        }
    }
    else
    {
          event->ignore();
    }
}