self.menu=QMenu()
self.menu.addAction('編輯', self.Action1)
self.menu.addAction('連接', self.Action2)
self.menu.addAction('刪除',self..deleteLater)
self.button.setMenu(self.menu)
self.button.show()

看起來你是把上面這些code加到你的View？你這樣2個btn不就要加2次？
你對物件導向的掌握還不夠，我不覺得你這樣學QT能學的成...
PyQT我也才剛學而已...

from PyQt5 import QtGui, QtCore
from PyQt5.QtWidgets import *
from PyQt5.QtCore import Qt, QMimeData
from PyQt5.QtGui import QDrag


class Window(QWidget):
    def __init__(self):
        QWidget.__init__(self)
        self.view = View(self)
        self.button = QPushButton('Clear View', self)
        self.button.clicked.connect(self.handleClearView)
        layout = QVBoxLayout(self)
        layout.addWidget(self.view)
        layout.addWidget(self.button)

    def handleClearView(self):
        self.view.scene().clear()


class DragButton(QPushButton):
    def __init__(self, title, parent=None):
        super().__init__(title, parent)
        self.setContextMenuPolicy(Qt.CustomContextMenu)
        self.customContextMenuRequested.connect(self.showMenu)
    
    def showMenu(self):
        menu=QMenu()
        menu.addAction('連接', self.connectLine)
        menu.addAction('刪除', self.deleteLine)
        menu.exec_(self.cursor().pos())

    def connectLine(self):
        view = self.parent()
        view.createLineItem()

    def deleteLine(self):
        view = self.parent()
        view.clearScene()
        
    def mouseMoveEvent(self, e):
        if e.buttons() != Qt.LeftButton:
            return

        mimeData = QMimeData()
        drag = QDrag(self)
        drag.setMimeData(mimeData)
        drag.setHotSpot(e.pos() - self.rect().topLeft())
        dropAction = drag.exec_(Qt.MoveAction)


class View(QGraphicsView):
    def __init__(self, parent):
        QGraphicsView.__init__(self, parent)
        self.setScene(QGraphicsScene(self))
        self.setAcceptDrops(True)
        self.setSceneRect(QtCore.QRectF(self.viewport().rect()))
        self.btn1=DragButton('Test1', self)
        self.btn2=DragButton('Test2', self)
        self.line = None

    def _createLineF(self):
        start = QtCore.QPointF(self.mapToScene(self.btn1.pos()))
        end = QtCore.QPointF(self.mapToScene(self.btn2.pos()))
        return QtCore.QLineF(start, end)

    def createLineItem(self):
        self.line = QGraphicsLineItem(self._createLineF())
        self.scene().addItem(self.line)

    def clearScene(self):
        self.scene().clear()
        self.line = None

    def dragEnterEvent(self, e):
        e.accept()

    def dragMoveEvent(self, e):
        e.accept()

    def dropEvent(self, e):
        btn = e.source()
        position = e.pos()
        btn.move(position)
        if self.line:
            self.line.setLine(self._createLineF())
        e.setDropAction(Qt.MoveAction)
        e.accept()


if __name__ == '__main__':

    import sys
    app = QApplication(sys.argv)
    window = Window()
    window.resize(640, 480)
    window.show()
    sys.exit(app.exec_())