本文通過Python3+PyQt5實現自定義部件–Counters自定 窗口部件。這個窗口是3*3的網格。本文有兩個例子如下：

/home/yrd/eric_workspace/chap11/counters.py。
/home/yrd/eric_workspace/chap11/counters_dnd.py

第二個例子在第一個例子的基礎上實現能通過鼠標拖拽球到不同的網格中。

/home/yrd/eric_workspace/chap11/counters.py

#!/usr/bin/env python3from PyQt5.QtCore import (QRectF, QSize, Qt)from PyQt5.QtWidgets import (QApplication, QSizePolicy,QWidget)from PyQt5.QtGui import QPainter,QPenBLANK, RED, YELLOW = range(3)class CountersWidget(QWidget):  def __init__(self, parent=None):    super(CountersWidget, self).__init__(parent)    self.setSizePolicy(QSizePolicy(QSizePolicy.Expanding,                    QSizePolicy.Expanding))    self.grid = [[BLANK] * 3 for i in range(3)]    self.selected = [0, 0]    self.setMinimumSize(self.minimumSizeHint())  def sizeHint(self):    return QSize(200, 200)  def minimumSizeHint(self):    return QSize(100, 100)  def mousePressEvent(self, event):    xOffset = self.width() / 3    yOffset = self.height() / 3    if event.x() < xOffset:      x = 0    elif event.x() < 2 * xOffset:      x = 1    else:      x = 2    if event.y() < yOffset:      y = 0    elif event.y() < 2 * yOffset:      y = 1    else:      y = 2    cell = self.grid[x][y]    if cell == BLANK:      cell = RED    elif cell == RED:      cell = YELLOW    else:      cell = BLANK    self.grid[x][y] = cell    self.selected = [x, y]    self.update()  def keyPressEvent(self, event):    if event.key() == Qt.Key_Left:      self.selected[0] = (2 if self.selected[0] == 0                else self.selected[0] - 1)    elif event.key() == Qt.Key_Right:      self.selected[0] = (0 if self.selected[0] == 2                else self.selected[0] + 1)    elif event.key() == Qt.Key_Up:      self.selected[1] = (2 if self.selected[1] == 0                else self.selected[1] - 1)    elif event.key() == Qt.Key_Down:      self.selected[1] = (0 if self.selected[1] == 2                else self.selected[1] + 1)    elif event.key() == Qt.Key_Space:      x, y = self.selected      cell = self.grid[x][y]      if cell == BLANK:        cell = RED      elif cell == RED:        cell = YELLOW      else:        cell = BLANK      self.grid[x][y] = cell    self.update()  def paintEvent(self, event=None):    painter = QPainter(self)    painter.setRenderHint(QPainter.Antialiasing, True)    xOffset = self.width() / 3    yOffset = self.height() / 3    for x in range(3):      for y in range(3):        cell = self.grid[x][y]        rect = (QRectF(x * xOffset, y * yOffset,            xOffset, yOffset).adjusted(0.5, 0.5, -0.5, -0.5))        color = None        if cell == RED:          color = Qt.red        elif cell == YELLOW:          color = Qt.yellow        if color is not None:          painter.save()          painter.setPen(Qt.black)          painter.setBrush(color)          painter.drawEllipse(rect.adjusted(2, 2, -2, -2))          painter.restore()        if [x, y] == self.selected:          painter.setPen(QPen(Qt.blue, 3))        else:          painter.setPen(Qt.black)        painter.drawRect(rect)if __name__ == "__main__":  import sys  app = QApplication(sys.argv)  form = CountersWidget()  form.setWindowTitle("Counters")  form.show()  app.exec_()