我正在嘗試編寫一個程序，該程序在按下箭頭鍵時顯示和循環(huán)顯示不同文件格式的圖像。我發(fā)現(xiàn)設置我的 reader->mapper->actor 管道然后啟動我的 RenderWindowInteractor 允許渲染 actor，但是將此代碼移動到 RenderWindowInteractor 的 KeyPressEvent 的回調(diào)不允許渲染 actor。一旦事件循環(huán)開始，是否需要額外的步驟來設置新的actor，或者我犯了其他錯誤？import vtk#Create the renderer that will display our actorsren = vtk.vtkRenderer()actor = None#Maps the data from the Nifti file 'filename' onto a vtkImageSlice actordef LoadNifti():    # load head MRI in NIFTI format    reader = vtk.vtkNIFTIImageReader()    reader.SetFileName("head.nii")    reader.Update()    # Add an ImageSliceMapper, which maps data to an ImageSlice Actor    mapper = vtk.vtkImageSliceMapper()    #Set the slice position to the camera focal point    mapper.SliceAtFocalPointOn()    mapper.SetInputConnection(reader.GetOutputPort())    # Add an ImageSlice actor, which represents a slice as an image    global actor    actor = vtk.vtkImageSlice()    actor.SetMapper(mapper)#Placeholder for when I have DICOM workingdef ShowDICOM(filename):    pass#Create a RenderWindow to display images from the RendererrenWin = vtk.vtkRenderWindow()renWin.AddRenderer(ren)#Wrap the RenderWindow in a RenderWindowInteractor to catch key and mouse eventsiren = vtk.vtkRenderWindowInteractor()iren.SetRenderWindow(renWin)def foo():    LoadNifti()    ren.AddActor(actor)##Extend the default functionality of the interactor and its style with custom listenersdef KeyPressEvent(obj, ev):    foo()    print("This verifies that the callback is triggered")iren.AddObserver("KeyPressEvent", KeyPressEvent)        #Start the program############################################################################ WHEN foo() IS PRESENT BELOW, THE ACTOR WILL RENDER IMMEDIATELY.# WHEN foo() IS ABSENT BELOW, CALLING foo() BY TRIGGERING THE KeyPressEvent# IS NOT SUFFICIENT TO HAVE THE ACTOR RENDER.###########################################################################foo()#According to the docs, the Start method will initialize iren and render renWin automaticallyiren.Start()