单击鼠标前激活事件（Python，Tkinter）

Question

我正在编写一些代码来移动 canvas 上绘制的形状。它总体上是一个矢量绘图程序，所以我需要能够移动一个形状，然后再移动另一个。

到目前为止，我已经有了可以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就跳了起来。我认为正在发生的事情是移动形状的代码在没有点击的情况下被激活，所以代码中的坐标没有被重置，导致形状跳跃（我的代码应该得到第二个的坐标我希望点击它时的形状）

出于任何原因，我尝试在线查找它无需点击即可运行的原因，但没有找到任何内容。我还尝试取消绑定在放置第一个形状后移动形状的标签，这样它们在单击第二个形状之前不会被绑定，但这似乎没有用。

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

要使用参数绑定函数，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 将在创建小部件之前调用回调函数，并将函数的 return 值传递给 Tkinter。 Tkinter 然后尝试将 return 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。这可能不是你想要的。

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

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