在鼠标单击之前激活的事件(Python，Tkinter)

Question

我正在研究一些代码来移动在画布上绘制的形状。总的来说，这是一个矢量绘图程序，所以我需要能够移动一个形状，然后移动另一个形状。

到目前为止，我有用于移动

一个形状的代码，但是当我随后尝试移动屏幕上的另一个形状时，该形状在我单击它之前跳跃。我认为正在发生的事情是，用于移动形状的代码无需单击即可激活，因此代码中的坐标没有被重置，导致形状跳跃（我希望我拥有的代码应该在单击时获得第二个形状的坐标）

我尝试在线查找它无需单击即可工作的任何原因，但没有找到任何东西。我还尝试取消绑定在放置第一个形状后移动形状的标签，以便在单击第二个形状之前不会绑定它们，但这似乎不起作用。

谁能解释一下这里发生了什么？

#code for a two shapes
circle = Main_Window.create_image(500,400, image = CircleIm, tags = "circle")
shape = circle
type1 = Move_Shape(shape)
Main_Window.tag_bind(circle, "<ButtonPress-3>", type1.moveShape(shape))
triangle= Main_Window.create_image(500,400, image = TriangleIm, tags = "triangle")
shape = triangle
type1 = Move_Shape(shape)
Main_Window.tag_bind(triangle, "<ButtonPress-3>", type1.moveShape(shape))

class Move_Shape:
    def __init__(self, shape):
        self.shape = shape
        return
def getShapeType(self, shape):
    global shapeType
    print(self.shape)
    shapeType = Main_Window.gettags(self.shape)  
    return shapeType
def moveShape(self, shape):
    #while left button is held down, we want it to move the tagged shape to     move to the position of the mouse
    global b1, currentX, currentY
    b1 = "down"
    newX, newY = None, None
    shapeType = self.getShapeType(shape)
    print(shapeType)
    Main_Window.addtag_withtag("move_shape", shapeType[0])
    #Bind move_shape to moving code
    print("new tags are", Main_Window.gettags(self.shape))
    Main_Window.tag_bind("move_shape","<Motion>", self.whileMoving)
    Main_Window.tag_bind("move_shape","<ButtonPress-3>", self.getCurrentCoords)
    Main_Window.tag_bind("move_shape", "<ButtonPress-1>", self.startMoving)
    Main_Window.tag_bind("move_shape", "<ButtonRelease-1>", self.stopMoving)
    root_window.mainloop() 
    return shape

def getCurrentCoords(self, event):
    global currentX, currentY
     #make sure the coordinates are obtained before user tries to move shape
    coords = Main_Window.coords(shapeType[0])
    currentX= coords[0]
    currentY = coords[1]
    return currentX, currentY
def startMoving(self,event):
    global b1
    b1 = "down"
    return
def stopMoving(self, event):
    global b1
    b1 = "up"
    newX = None     
    newY = None
    return b1, newX, newY
def whileMoving(self, event):
    global shapeType, b1, currentX, currentY
    if b1 == "down":
        newX = event.x
        newY = event.y
        if newX is not None  and newY is not None:
            x = newX - currentX
            y = newY - currentY
            Main_Window.move(shapeType[0],x,y)
            currentX = newX
            currentY = newY
            newX = event.x
            newY= event.y
        return

Answer 1

要将函数与参数绑定，请使用lambda关键字：

Main_Window.tag_bind(triangle, "<ButtonPress-3>", lambda shape: type1.moveShape(shape))  

如果你这样做Main_Window.tag_bind(triangle, "<ButtonPress-3>", type1.moveShape(shape))，Python 会在创建小部件之前调用回调函数，并将函数的返回值传递给 Tkinter。然后，Tkinter 尝试将返回值转换为字符串，并告诉 Tk 在激活按钮时调用具有该名称的函数。这可能不是您想要的。

对于像这样的简单情况，您可以使用 lambda 表达式作为 Tkinter 和回调函数之间的链接（我接受了 effbot.org 的解释）