使用QGraphicsScene中的selectionChanged信号addRect围绕选定的项目

Question

我想绘制在场景中选择的项目（通过RubberBandDrag或Ctrl +点击每个项目）周围的矩形。

为了做到这一点，我子类QGraphicsScene并重新实现了selectionChanged方法添加所选区域周围QGraphicsRectItem，但由于某些原因，当选择场景中所未选定项目不会被调用此方法。我确定这些项目实际上是可选择的。

这里是我想要做的一个小例子：

from PyQt4.QtGui import * 
from PyQt4.QtCore import * 
import sys 

class DiagramScene(QGraphicsScene): 

    def __init__(self, parent=None): 
     super().__init__(parent) 

     self.selRect = None 

    def selectionChanged(self): 
     area = self.selectionArea().boundingRect() 
     pen = QPen() 
     pen.setColor(Qt.black) 
     pen.setStyle(Qt.DashLine) 

     self.selRect = self.addRect(area, pen) 


if __name__ == "__main__": 

    app = QApplication(sys.argv) 

    view = QGraphicsView() 
    view.setDragMode(QGraphicsView.RubberBandDrag) 

    scene = DiagramScene() 

    scene.setSceneRect(0, 0, 500, 500) 

    rect1 = scene.addRect(20, 20, 100, 50) 
    rect2 = scene.addRect(80, 80, 100, 50) 
    rect3 = scene.addRect(140, 140, 100, 50) 

    rect1.setFlag(QGraphicsItem.ItemIsSelectable, True) 
    rect2.setFlag(QGraphicsItem.ItemIsSelectable, True) 
    rect3.setFlag(QGraphicsItem.ItemIsSelectable, True) 

    view.setScene(scene) 
    view.show() 

    sys.exit(app.exec_()) 

Answer 1

selectionChanged是一个信号，不是说你必须实现的方法。你需要做的是将此信号连接到插槽，并在插槽中实现，所以无论何时发出信号，代码都会执行：

from PyQt4.QtGui import * 
from PyQt4.QtCore import * 
import sys 

class DiagramScene(QGraphicsScene): 

    def __init__(self, parent=None): 
     super().__init__(parent) 
     self.selRect = None 
     self.selectionChanged.connect(self.onSelectionChanged) 

    @pyqtSlot() 
    def onSelectionChanged(self): 
     area = self.selectionArea().boundingRect() 
     pen = QPen() 
     pen.setColor(Qt.black) 
     pen.setStyle(Qt.DashLine) 
     self.selRect = self.addRect(area, pen) 


if __name__ == "__main__": 

    app = QApplication(sys.argv) 

    view = QGraphicsView() 
    view.setDragMode(QGraphicsView.RubberBandDrag) 

    scene = DiagramScene() 

    scene.setSceneRect(0, 0, 500, 500) 

    rect1 = scene.addRect(20, 20, 100, 50) 
    rect2 = scene.addRect(80, 80, 100, 50) 
    rect3 = scene.addRect(140, 140, 100, 50) 

    rect1.setFlag(QGraphicsItem.ItemIsSelectable, True) 
    rect2.setFlag(QGraphicsItem.ItemIsSelectable, True) 
    rect3.setFlag(QGraphicsItem.ItemIsSelectable, True) 

    view.setScene(scene) 
    view.show() 

    sys.exit(app.exec_())