QT與不少GUI庫不一樣(如MFC),它不能隨時隨地地在界面上畫圖,只能在界面類的painterEvent中畫圖,如此一來,想在繪製QT界面時使用狀態模式(GOF的23種設計模式之一)就有點困難了,做爲解決方案,我先把要界面上的圖片繪製在一張圖片上(QPixmap),而後再在painterEvent中將Pixmap「畫」到界面上。如下是這種方法的一個小例子。設計模式
#include <QtGui> //狀態類的基類,定義了各個公用接口, //其中,SetPixmap是一個純虛接口 class BasePen { protected: //這三個類成員理應是BasePen的私有成員,而後經過接口訪問 //我這裏爲了方便,直接把它們設爲保護成員了 QPixmap m_Pixmap; QPoint m_StartPoint; QPoint m_EndPoint; virtual void SetPixmap() = 0; public: BasePen() { m_StartPoint = m_EndPoint = QPoint(0, 0); m_Pixmap = QPixmap(500, 500); } void SetStartPoint(QPoint point) { m_StartPoint = point; } void SetEndPoint(QPoint point) { m_EndPoint = point; SetPixmap(); } QPixmap GetPixmap() { return m_Pixmap; } }; //矩形類,在界面上畫一個紅色的矩形 class RectPen : public BasePen { protected: void SetPixmap() { m_Pixmap.fill(Qt::white); QPainter painter(&m_Pixmap); QRect rect(m_StartPoint, m_EndPoint); painter.setPen(Qt::red); painter.drawRect(rect); } }; //直線類,在界面上畫一條藍色的直線 class LinePen : public BasePen { protected: void SetPixmap() { m_Pixmap.fill(Qt::white); QPainter painter(&m_Pixmap); painter.setPen(Qt::blue); painter.drawLine(m_StartPoint, m_EndPoint); } }; //圓形類,在界面上畫一個綠色的橢圓 class CirclePen : public BasePen { protected: void SetPixmap() { m_Pixmap.fill(Qt::white); QPainter painter(&m_Pixmap); QRect rect(m_StartPoint, m_EndPoint); painter.setPen(Qt::green); painter.drawEllipse(rect); } }; class Widget : public QWidget { Q_OBJECT private: bool m_MouseDown; BasePen *m_BasePen; RectPen *m_RectPen; LinePen *m_LinePen; CirclePen *m_CirclePen; //在界面上放三個按鈕,用來控制畫圖狀態 QRadioButton *m_LineButton; QRadioButton *m_RectButton; QRadioButton *m_CircleButton; protected: void mousePressEvent(QMouseEvent *event); void mouseMoveEvent(QMouseEvent *event); void mouseReleaseEvent(QMouseEvent *event); void paintEvent(QPaintEvent *event); public: Widget(QWidget *parent = 0); ~Widget(); private slots: void ClickedLineButton() { m_BasePen = m_LinePen; } void ClickedRectButton() { m_BasePen = m_RectPen; } void ClickedCircleButton() { m_BasePen = m_CirclePen; } }; Widget::Widget(QWidget *parent /* = 0 */) : QWidget(parent) { m_MouseDown = false; m_RectPen = new RectPen; m_LinePen = new LinePen; m_CirclePen = new CirclePen; m_LineButton = new QRadioButton("Line", this); m_RectButton = new QRadioButton("Rect", this); m_CircleButton = new QRadioButton("Circle", this); m_LineButton->move(10, 10); m_RectButton->move(100, 10); m_CircleButton->move(200, 10); connect(m_LineButton, SIGNAL(clicked()), this, SLOT(ClickedLineButton())); connect(m_RectButton, SIGNAL(clicked()), this, SLOT(ClickedRectButton())); connect(m_CircleButton, SIGNAL(clicked()), this, SLOT(ClickedCircleButton())); m_BasePen = m_LinePen; m_LineButton->setChecked(true); setFixedSize(500, 500); } Widget::~Widget() { delete m_LinePen; delete m_RectPen; delete m_CirclePen; } void Widget::mousePressEvent(QMouseEvent *event) { if( event->button() == Qt::LeftButton ) { m_MouseDown = true; m_BasePen->SetStartPoint(event->pos()); } } void Widget::mouseMoveEvent(QMouseEvent *event) { if( m_MouseDown ) { m_BasePen->SetEndPoint(event->pos()); update(); } } void Widget::mouseReleaseEvent(QMouseEvent *event) { if( event->button() == Qt::LeftButton ) { m_MouseDown = false; } } void Widget::paintEvent(QPaintEvent *event) { QPixmap temp = m_BasePen->GetPixmap(); QPainter painter(this); painter.drawPixmap(0, 0, temp); } #include "main.moc" int main(int argc, char **argv) { QApplication app(argc, argv); Widget *ww = new Widget; ww->show(); return app.exec(); }