覆盖鼠标事件后自定义 QGraphicsItem 不需要的行为

Question

我正在尝试为棋盘建模，我希望将棋子 GraphicsItem 对象放置在案例 GraphicsItem 对象的中心。

我只为 pawn 对象实现了一个 mouseRelease 事件，它检查该位置的项目列表，如果存在案例，我将 pawn 放在案例位置。

现在在窗口中尝试第一次移动时它可以正常工作，但之后当我尝试移动棋子时它会回到原来的位置我仍然可以移动它但它不在鼠标光标下

代码如下：

import sys
from PyQt5.QtWidgets import (QApplication, QWidget, QGridLayout,
                             QGraphicsView, QGraphicsScene, QGraphicsItem)
from PyQt5.QtGui import QPen, QBrush, QTransform
from PyQt5.QtCore import Qt, QRectF, QPointF

class Pawn(QGraphicsItem):
    def __init__(self, parent = None):
        super().__init__(parent)
        self.setFlag(QGraphicsItem.ItemIsMovable)
        self.setPos(0, 0)
        self.setZValue(1)

        self.originalPos = self.scenePos()

    def paint(self, painter, options, widget):
        painter.setBrush(Qt.white)
        painter.drawEllipse(0, 0, 30, 30)

    def boundingRect(self):
        return QRectF(0, 0, 30, 30)

    def mouseReleaseEvent(self, event):
        dropPos = self.mapToScene(event.pos())
        dropCase = None
        for item in self.scene().items(dropPos.x(), dropPos.y(), 0.0001, 0.0001,
                                       Qt.IntersectsItemShape, 
                                       Qt.AscendingOrder):
            if isinstance(item, Case):
                dropCase = item

        if dropCase:
            newP = dropCase.scenePos()
            self.setPos(newP)
            self.originalPos = newP

        else:
            self.setPos(self.originalPos)


class Case(QGraphicsItem):
    def __init__(self, parent = None):
        super().__init__(parent)
        self.setPos(100, 0)
        self.setZValue(0)

    def paint(self, painter, options, widget):
        painter.setPen(Qt.black)
        painter.setBrush(Qt.black)
        painter.drawRect(0, 0, 40, 40)

    def boundingRect(self):
        return QRectF(0, 0, 40, 40)

    def getCenter(self):
        x, y = self.scenePos().x() + 10, self.scenePos().y() + 10
        return QPointF(x, y)

class MainWin(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        scene = QGraphicsScene()
        view = QGraphicsView(scene, self)
        view.setGeometry(0, 0, 290, 290)

        case = Case()
        pawn = Pawn()
        scene.addItem(case)
        scene.addItem(pawn)

        self.setWindowTitle('doodling')
        self.setGeometry(200, 200, 300, 300)
        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWin()
    sys.exit(app.exec_())

Answer 1

我没有实现 mouseMoveEvent，因为我将它与悬停行为混淆了。

此代码按预期工作

from PyQt5.QtWidgets import (QApplication, QWidget, QGridLayout,
                             QGraphicsView, QGraphicsScene, QGraphicsItem)
from PyQt5.QtGui import QPen, QBrush, QTransform
from PyQt5.QtCore import Qt, QRectF, QPointF

class Pawn(QGraphicsItem):
    def __init__(self, parent = None):
        super().__init__(parent)
        self.setFlag(QGraphicsItem.ItemIsMovable)
        self.setPos(0, 0)
        self.setZValue(1)

        self.originalPos = self.scenePos()

    def paint(self, painter, options, widget):
        painter.setBrush(Qt.white)
        painter.drawEllipse(0, 0, 30, 30)

    def boundingRect(self):
        return QRectF(0, 0, 30, 30)

    def mouseMoveEvent(self, event):
        movePos = self.mapToScene(event.pos())
        self.setPos(movePos.x(), movePos.y())

    def mouseReleaseEvent(self, event):
        dropPos = self.mapToScene(event.pos())
        dropCase = None
        for item in self.scene().items(dropPos.x(), dropPos.y(), 0.0001, 0.0001,
                                       Qt.IntersectsItemShape, 
                                       Qt.AscendingOrder):
            if isinstance(item, Case):
                dropCase = item

        if dropCase:
            newP = dropCase.scenePos()
            self.setPos(newP)
            self.originalPos = newP
        else:
            self.setPos(self.originalPos)


class Case(QGraphicsItem):
    def __init__(self, x_coord, y_coord, parent = None):
        super().__init__(parent)
        self.setPos(x_coord, y_coord)
        self.setZValue(0)

    def paint(self, painter, options, widget):
        painter.setPen(Qt.black)
        painter.setBrush(Qt.black)
        painter.drawRect(0, 0, 40, 40)

    def boundingRect(self):
        return QRectF(0, 0, 40, 40)

    def getCenter(self):
        x, y = self.scenePos().x() + 10, self.scenePos().y() + 10
        return QPointF(x, y)

class MainWin(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        scene = QGraphicsScene()
        view = QGraphicsView(scene, self)
        view.setGeometry(0, 0, 290, 290)

        case1 = Case(-100, 0)
        case2 = Case(100, 0)
        pawn = Pawn()
        scene.addItem(case1)
        scene.addItem(case2)
        scene.addItem(pawn)

        self.setWindowTitle('doodling')
        self.setGeometry(200, 200, 300, 300)
        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWin()
    sys.exit(app.exec_())