Tkinter create_oval 方法不改变颜色

Question

我使用了按钮，因此当单击它们时，它们会更改椭圆的颜色以明显绘制。 问题是无论我如何更改颜色变量，它总是会创建一个白色椭圆形。 有什么帮助吗？

代码：

from tkinter import *

master = Tk()
master.title('Painting in Python')

canvas_width = 600
canvas_height = 450
color='white'
bg ='black'

def REDPEN():
    color='red'
    print(color)
def BLUEPEN():
    color='blue'
    print(color)
def GREENPEN():
    color='green'
    print(color)

def paint(event):
    x1,y1=(event.x-1),(event.y-1)
    x2,y2=(event.x+1),(event.y+1)
    c.create_oval(x1,y1,x2,y2,fill=color,outline=color,width=0)

RedButton = Button(master, text = "RED", command =REDPEN)
BlueButton = Button(master, text = "BLUE", command =BLUEPEN)
GreenButton = Button(master, text = "GREEN", command =GREENPEN)

RedButton.pack()
BlueButton.pack()
GreenButton.pack()


c=Canvas(master,width=canvas_width,height=canvas_height,bg=bg)

c.pack(expand=YES,fill=BOTH)
c.bind('<B1-Motion>',paint)

message=Label(master,text='Press and Drag to draw')
message.pack(side=BOTTOM)
master.mainloop()

Answer 1

当您在函数中更改颜色变量的值时，主颜色变量中没有反映相同的值，这就是您的问题的原因，因为您从未告诉 python function 内部和 ZC1C4252678E68385D1AAB5相同，因此 python 认为两者是不同的，一个是本地的，另一个是全局的。

一个简单的解决方法是向 python 声明，当您使用全局关键字 python 在其他函数中使用全局颜色变量时，您指的是全局颜色变量，这解决了您的问题 - ：

from tkinter import *

master = Tk()
master.title('Painting in Python')

canvas_width = 600
canvas_height = 450
color='white'
bg ='black'

def REDPEN():
    global color
    color='red'
    print(color)
def BLUEPEN():
    global color
    color='blue'
    print(color)
def GREENPEN():
    global color
    color='green'
    print(color)

def paint(event):
    global color
    x1,y1=(event.x-1),(event.y-1)
    x2,y2=(event.x+1),(event.y+1)
    c.create_oval(x1,y1,x2,y2,fill=color,outline=color,width=0)

RedButton = Button(master, text = "RED", command =REDPEN)
BlueButton = Button(master, text = "BLUE", command =BLUEPEN)
GreenButton = Button(master, text = "GREEN", command =GREENPEN)

RedButton.pack()
BlueButton.pack()
GreenButton.pack()


c=Canvas(master,width=canvas_width,height=canvas_height,bg=bg)

c.pack(expand=YES,fill=BOTH)
c.bind('<B1-Motion>',paint)

message=Label(master,text='Press and Drag to draw')
message.pack(side=BOTTOM)
master.mainloop()