如何在 Python 中使用按钮在画布上移动项目？

Question

我正在尝试修改此处发布的示例脚本：

board-drawing code to move an oval

原始脚本允许您在画布上单击和拖动对象。我对其进行了更改，以便按钮可以移动第一个对象，但出现按钮错误： TypeError: button_move() 正好需要 2 个参数（1 个给定） 我不明白第二个参数应该是什么。

这是修改后的脚本：

import Tkinter as tk

class Example(tk.Frame):
    '''Illustrate how to drag items on a Tkinter canvas'''

    def __init__(self, parent):
        tk.Frame.__init__(self, parent)

        # create a canvas
        self.canvas = tk.Canvas(width=400, height=400)
        self.canvas.pack(fill="both", expand=True)

        # this data is used to keep track of an 
        # item being dragged
        self._drag_data = {"x": 0, "y": 0, "item": None}

        # create a couple of movable objects
        self._create_token((100, 100), "white")
        self._create_token((200, 100), "black")

        # add bindings for clicking, dragging and releasing over
        # any object with the "token" tag
        self.canvas.tag_bind("token", "<ButtonPress-1>", self.on_token_press)
        self.canvas.tag_bind("token", "<ButtonRelease-1>", self.on_token_release)
        self.canvas.tag_bind("token", "<B1-Motion>", self.on_token_motion)
#-----------------------------------------------------------------------------
        self.canvas.button2 = tk.Button(self.canvas, text="Button Test",
                                 command=self.button_move)
        self.canvas.button2.config(bg="cyan",fg="black")
        self.canvas.button2.pack(side='top')

        self.canvas.tag_bind("button2", "<ButtonPress-1>", self.button_move)
#-----------------------------------------------------------------------------
    def _create_token(self, coord, color):
        '''Create a token at the given coordinate in the given color'''
        (x,y) = coord
        self.canvas.create_oval(x-25, y-25, x+25, y+25, 
                                outline=color, fill=color, tags="token")

    def on_token_press(self, event):
        '''Begining drag of an object'''
        # record the item and its location
        self._drag_data["item"] = self.canvas.find_closest(event.x, event.y)[0]
        self._drag_data["x"] = event.x
        self._drag_data["y"] = event.y

    def on_token_release(self, event):
        '''End drag of an object'''
        # reset the drag information
        self._drag_data["item"] = None
        self._drag_data["x"] = 0
        self._drag_data["y"] = 0

    def on_token_motion(self, event):
        '''Handle dragging of an object'''
        # compute how much the mouse has moved
        delta_x = event.x - self._drag_data["x"]
        delta_y = event.y - self._drag_data["y"]
        # move the object the appropriate amount
        self.canvas.move(self._drag_data["item"], delta_x, delta_y)
        # record the new position
        self._drag_data["x"] = event.x
        self._drag_data["y"] = event.y
#-----------------------------------------------------------------------------
    def button_move(self, event):
        '''Handle dragging of an object'''
        # set movement amount
        delta_x = 15
        delta_y = 15
        # move the object the appropriate amount
        #self.canvas.move(self._drag_data["item"], delta_x, delta_y)
        self.canvas.move(self._drag_data[1], delta_x, delta_y)
        # record the new position
        self._drag_data["x"] = event.x
        self._drag_data["y"] = event.y
#-----------------------------------------------------------------------------
if __name__ == "__main__":
    root = tk.Tk()
    Example(root).pack(fill="both", expand=True)
    root.mainloop()

Answer 1

command= 在没有 event 的情况下执行函数，但您分配的函数需要 event - command=self.button_move -> def button_move(self, event)

但bind 与event 执行相同的功能，因此您需要此功能与event。

解决方法：使用默认值，即None

def button_move(self, event=None):

但是如果你用command=执行什么，你不能在这个函数中使用event.x，event.y

Answer 2

这是使用 furas 建议的更新代码：

import Tkinter as tk

class Example(tk.Frame):
    '''Illustrate how to drag items on a Tkinter canvas'''

    def __init__(self, parent):
        tk.Frame.__init__(self, parent)

        # create a canvas
        self.canvas = tk.Canvas(width=400, height=400)
        self.canvas.pack(fill="both", expand=True)

        # this data is used to keep track of an 
        # item being dragged
        self._drag_data = {"x": 0, "y": 0, "item": None}

        # create a couple of movable objects
        self._create_token((100, 100), "white")
        self._create_token((200, 100), "black")

        # add bindings for clicking, dragging and releasing over
        # any object with the "token" tag
        self.canvas.tag_bind("token", "<ButtonPress-1>", self.on_token_press)
        self.canvas.tag_bind("token", "<ButtonRelease-1>", self.on_token_release)
        self.canvas.tag_bind("token", "<B1-Motion>", self.on_token_motion)
#-----------------------------------------------------------------------------
        self.canvas.button2 = tk.Button(self.canvas, text="Button Test",
                                 command=self.button_move)
        self.canvas.button2.config(bg="cyan",fg="black")
        self.canvas.button2.pack(side='top')

        self.canvas.tag_bind("button2", "<ButtonPress-1>", self.button_move)
#-----------------------------------------------------------------------------
    def _create_token(self, coord, color):
        '''Create a token at the given coordinate in the given color'''
        (x,y) = coord
        self.canvas.create_oval(x-25, y-25, x+25, y+25, 
                                outline=color, fill=color, tags="token")

    def on_token_press(self, event):
        '''Begining drag of an object'''
        # record the item and its location
        self._drag_data["item"] = self.canvas.find_closest(event.x, event.y)[0]
        self._drag_data["x"] = event.x
        self._drag_data["y"] = event.y

    def on_token_release(self, event):
        '''End drag of an object'''
        # reset the drag information
        self._drag_data["item"] = None
        self._drag_data["x"] = 0
        self._drag_data["y"] = 0

    def on_token_motion(self, event):
        '''Handle dragging of an object'''
        # compute how much the mouse has moved
        delta_x = event.x - self._drag_data["x"]
        delta_y = event.y - self._drag_data["y"]
        # move the object the appropriate amount
        self.canvas.move(self._drag_data["item"], delta_x, delta_y)
        # record the new position
        self._drag_data["x"] = event.x
        self._drag_data["y"] = event.y
#-----------------------------------------------------------------------------
    def button_move(self, event=None):
        '''Handle dragging of an object'''
        # set movement amount
        delta_x = 15
        delta_y = 15
        # move the object the appropriate amount
        #self.canvas.move(self._drag_data["item"], delta_x, delta_y)
        #self.canvas.move(self._drag_data[1], delta_x, delta_y)
        self.canvas.move(1, delta_x, delta_y) # moves item 1, when cursor is over token
        # record the new position
        #self._drag_data["x"] = event.x
        #self._drag_data["y"] = event.y
#-----------------------------------------------------------------------------
if __name__ == "__main__":
    root = tk.Tk()
    Example(root).pack(fill="both", expand=True)
    root.mainloop()

Answer 3

当你将一个回调如button_move()配置为按钮的command时，它被调用时唯一给它的参数是self，就像你这样调用它：

self.button_move()

但是因为 button_move() 还需要一个 event 参数，所以您会收到以下错误：

TypeError: button_move() takes exactly 2 arguments (1 given).

因此从button_move() 定义中删除event 参数将是第一步。

另外，由于event 不在button_move() 范围内，您应该删除这两行：

self._drag_data["x"] = event.x
self._drag_data["y"] = event.y

最后，您需要从要移动的画布对象中获取 id，以便 self.canvas.move() 行工作。我建议您删除该行

self._drag_data["item"] = None

来自on_token_release()，因此最后点击的画布对象的id保存在self._drag_data["item"]中。那么你需要做的就是在尝试调用canvas.move()之前检查self._drag_data["item"]是否不是None。

应用所有这些更改会产生以下代码：

import Tkinter as tk

class Example(tk.Frame):
    '''Illustrate how to drag items on a Tkinter canvas'''

    def __init__(self, parent):
        tk.Frame.__init__(self, parent)

        # create a canvas
        self.canvas = tk.Canvas(width=400, height=400)
        self.canvas.pack(fill="both", expand=True)

        # this data is used to keep track of an
        # item being dragged
        self._drag_data = {"x": 0, "y": 0, "item": None}

        # create a couple of movable objects
        self._create_token((100, 100), "white")
        self._create_token((200, 100), "black")

        # add bindings for clicking, dragging and releasing over
        # any object with the "token" tag
        self.canvas.tag_bind("token", "<ButtonPress-1>", self.on_token_press)
        self.canvas.tag_bind("token", "<ButtonRelease-1>", self.on_token_release)
        self.canvas.tag_bind("token", "<B1-Motion>", self.on_token_motion)

        self.canvas.button2 = tk.Button(self.canvas, text="Button Test",
                                 command=self.button_move)
        self.canvas.button2.config(bg="cyan",fg="black")
        self.canvas.button2.pack(side='top')

        self.canvas.tag_bind("button2", "<ButtonPress-1>", self.button_move)

    def _create_token(self, coord, color):
        '''Create a token at the given coordinate in the given color'''
        (x,y) = coord
        self.canvas.create_oval(x-25, y-25, x+25, y+25,
                                outline=color, fill=color, tags="token")

    def on_token_press(self, event):
        '''Begining drag of an object'''
        # record the item and its location
        self._drag_data["item"] = self.canvas.find_closest(event.x, event.y)[0]
        self._drag_data["x"] = event.x
        self._drag_data["y"] = event.y

    def on_token_release(self, event):
        '''End drag of an object'''
        # reset the drag information
        self._drag_data["x"] = 0
        self._drag_data["y"] = 0

    def on_token_motion(self, event):
        '''Handle dragging of an object'''
        # compute how much the mouse has moved
        delta_x = event.x - self._drag_data["x"]
        delta_y = event.y - self._drag_data["y"]
        # move the object the appropriate amount
        self.canvas.move(self._drag_data["item"], delta_x, delta_y)
        # record the new position
        self._drag_data["x"] = event.x
        self._drag_data["y"] = event.y

    def button_move(self):
        if not self._drag_data["item"]:
            return

        '''Handle dragging of an object'''
        # set movement amount
        delta_x = 15
        delta_y = 15
        # move the object the appropriate amount
        #self.canvas.move(self._drag_data["item"], delta_x, delta_y)
        self.canvas.move(self._drag_data["item"], delta_x, delta_y)

if __name__ == "__main__":
    root = tk.Tk()
    Example(root).pack(fill="both", expand=True)
    root.mainloop()