使用QGraphicsScene中的selectionChanged信號addRect圍繞選定的項目

Question

我想繪製在場景中選擇的項目（通過RubberBandDrag或Ctrl +點擊每個項目）周圍的矩形。

爲了做到這一點，我子類QGraphicsScene並重新實現了selectionChanged方法添加所選區域周圍QGraphicsRectItem，但由於某些原因，當選擇場景中所未選定項目不會被調用此方法。我確定這些項目實際上是可選擇的。

這裏是我想要做的一個小例子：

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是一個信號，不是說你必須實現的方法。你需要做的是將此信號連接到插槽，並在插槽中實現，所以無論何時發出信號，代碼都會執行：

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_())