Question

我正在玩Qt教程中的一些代码并且因为我的一个QWidget继承类调用update（QRegion＆amp;）但它没有触发对paintEvent（..）的调用而被卡住了 - 基本上我试图在Qt教程的第12章中使用CannonShot类添加教程源代码的简单重构（参见链接：http://doc.trolltech.com/4.3/tutorial-t12.html）

CannonField update（）仍然可以正常工作并导致其paintEvent重新实现被调用。它唯一没有调用自己的paintEvent的CannonShot的update（）。（我已经确认它确实在更新调用之前和之后获得）。以下是一些片段：

class CannonShot : public QWidget
{
   Q_OBJECT
public:
   CannonShot(QWidget *parent = 0);
   int angle() const { return shotAngle; }
   int force() const { return shotForce; }
   void shoot();
private slots:
   void moveShot();
   void plotShot();

signals:
   void hit();
   void missed();
   void angleChanged(int);
   void forceChanged(int);
...
...
protected:
   paintEvent(QPaintEvent*);

private:
   int shotTimerCount;
   QTimer* autoShotTimer;
   float shotAngle;
   float shotForce;
};

这是CannonShot的构造函数的片段，并且调用了update（）：

CannonShot::CannonShot(QWidget *parent): QWidget(parent)
{
   shotTimerCount = 0;
   autoShotTimer = new QTimer(this);
   connect(autoShotTimer, SIGNAL(timeout()), this, SLOT(moveShot()));
}

void CannonShot::shoot()
{
   if (autoShotTimer->isActive())
   return;
   shotTimerCount = 0;
   shotAngle = CannonField::angle();
   shotForce = CannonField::force();
   autoShotTimer->start(5);
}

void CannonShot::moveShot()
{
   QRegion region = shotRect();
   ++shotTimerCount;

   QRect shotR = shotRect();
   if (shotR.x() > width() || shotR.y() > height()) {
      autoShotTimer->stop();
      emit missed();
   }
   else {
      region = region.unite(shotR);
   }
   update(region); //-Checked that code reaches before and after this call!
}

void CannonShot::paintEvent(QPaintEvent*)
{
   //-Never gets here!!
   QPainter painter(this);
   QColor color;
   //-Do whatever
}

这里还有一个简短的CannonField片段，其中包含镜头并调用shoot（）来解雇它们。

class CannonField : public QWidget
{
   Q_OBJECT

public:
   CannonField(QWidget *parent = 0);
   ~CannonField();
   static int angle() { return currentAngle; }
   static int force() { return currentForce; }

public slots:
   void setAngle(int angle);
   void setForce(int force);
   void shoot();

signals:
   void hit();
   void missed();
...
...

protected:
   void paintEvent(QPaintEvent *event);

public:
   static int currentAngle;
   static int currentForce;

private:
   QVector<CannonShot*> shots;
};

这是一个CannonField的源代码片段，用于射击。

void CannonField::shoot()
{
   //-Added this argument since I though after searching that CannonShot 
   // needs to have a QWidget with some dimensions..
   shots.push_back(new CannonShot(this));
   (shots.back())->shoot();
}

最后，驱动程序看起来像：

class MyWidget : public QWidget {
public:
   MyWidget(QWidget *parent = 0);
};

MyWidget::MyWidget(QWidget *parent): QWidget(parent)
{
   QPushButton *quit = new QPushButton(tr("&Quit"));
   quit->setFont(QFont("Times", 18, QFont::Bold));
   connect(quit, SIGNAL(clicked()), qApp, SLOT(quit()));
   LCDRange *angle = new LCDRange(tr("&ANGLE"));
   angle->setRange(0, 90);
   LCDRange *force = new LCDRange(tr("&FORCE"));
   force->setRange(10, 50);
   CannonField *cannonField = new CannonField(this);
   connect(angle, SIGNAL(valueChanged(int)),
          cannonField, SLOT(setAngle(int)));
   connect(cannonField, SIGNAL(angleChanged(int)),
          angle, SLOT(setValue(int)));
   connect(force, SIGNAL(valueChanged(int)),
          cannonField, SLOT(setForce(int)));
   connect(cannonField, SIGNAL(forceChanged(int)),
          force, SLOT(setValue(int)));
   QPushButton *shoot = new QPushButton(tr("&Shoot"));
   shoot->setFont(QFont("Times", 18, QFont::Bold));
   connect(shoot, SIGNAL(clicked()), cannonField, SLOT(shoot()));      
   ...
   ...
   //-Other layout stuff
}

int main(int argc, char *argv[])
{
   QApplication app(argc, argv);
   MyWidget widget;
   widget.setMinimumSize(300, 300);
   widget.setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
   widget.setGeometry(100, 100, 500, 355);
   widget.show();
   return app.exec();
}

Answer 1

如果QRegion :: isEmpty（）为true，则不会调用QWidget :: paintEvent（）。我怀疑你的情况可能会发生。

Answer 2

paintEvent(QPaintEvent*)函数应位于protected部分，函数签名为：

void QWidget::paintEvent ( QPaintEvent * event )   [virtual protected]

目前你有：

private:
paintEvent(QPaintEvent*);

应该是：

protected:
virtual void paintEvent(QPaintEvent*);

代替。

Answer 3

如果更新区域未与帧区域相交，则可能发生：

QRect frameRect = this->rect();

if( frameRect.intersected(updateRec).isEmpty())
{

}

Qt调用更新（QRegion＆amp;）不触发对paintEvent（..）的调用

3 个答案: