为什么我的Tkinter画布显示？

Question

我试图产生一个星算法使用Tkinter二维图形用户界面。我修改了以下代码，原来是在这里找到的：

from tkinter import *

class CellGrid(Canvas):
    def __init__(self,master, rowNumber, columnNumber, cellSize, theMap):
        Canvas.__init__(self, master, width = cellSize * columnNumber , height = cellSize * rowNumber)

        self.cellSize = cellSize

        self.grid = []
        for row in range(rowNumber):
            line = []
            for column in range(columnNumber):
                line.append(Cell(self, column, row, cellSize, theMap[row][column]))
            self.grid.append(line)

        print (self.grid[0][0].value)
        self.draw()

    def draw(self):
        for row in self.grid:
            for cell in row:
                cell.draw()

class Cell():
    colors = {
            0: 'white',    # untried
            1: 'black',    # obstacle
            2: 'green',    # start
            3: 'red',      # finish
            4: 'blue',     # open
            5: 'gray',     # closed
            6: 'orange',   # path
         }

    def __init__(self, master, x, y, size, value):
        self.master = master
        self.abs = x
        self.ord = y
        self.size= size
        self.fill = "white"
        self.value = value


    def setValue(self, value):
        self.value = value

    def draw(self):
         if self.master != None :
            if self.value == 0:
                self.fill = self.white
            elif self.value == 1:
                self.fill = self.black
            elif self.value == 2:
                self.fill = self.green
            elif self.value == 3:
                self.fill = self.red
            elif self.value == 4:
                self.fill = self.blue
            elif self.value == 5:
                self.fill = self.gray
            elif self.value == 6:
                self.fill = self.orange

            xmin = self.abs * self.size
            xmax = xmin + self.size
            ymin = self.ord * self.size
            ymax = ymin + self.size

            self.master.create_rectangle(xmin, ymin, xmax, ymax, fill = self.fill, outline = "black")

def main():
    Map = [
            [2, 0, 0, 0, 0],
            [0, 1, 1, 1, 1],
            [0, 1, 3, 0, 0],
            [0, 1, 1, 1, 0],
            [0, 0, 0, 0, 0],
          ]
    root = Tk()
    c = tk.Canvas(root, height=1000, width=1000, bg='white')
    my_gui = CellGrid(root, len(Map), len(Map[0]), 40, Map)


    root.mainloop()

但当我去运行它时，什么都没有显示。你知道吗

Answer 1

许多小的和不小的误解阻碍了星型算法的显示。你知道吗

问题1-调用main()函数不完整。你知道吗

As @avysk suggests as comment, the first blocking point is due to the missing of main() preamble in Python.

只需在def main()函数后添加以下代码：

if __name__ == '__main__':
    main()

问题2-主Canvas显示器输入错误和pack()丢失。你知道吗

因为tk符号没有定义，所以主画布声明如下：

c = Canvas(root, height=1000, width=1000, bg='white')

而不是：

c = tk.Canvas(root, height=1000, width=1000, bg='white')

在神奇的缺失调用之后是pack()：

c.pack() # magic call to display the (1000 x 1000) white canvas

问题3-缺少对辅助Canvas显示的调用。你知道吗

至于主Canvas，它缺少pack()的调用，可以使用两种可能性来显示次Canvas。你知道吗

1. 添加my_gui.pack()使主Canvas与次Canvas的大小相匹配
2. 或者我的首选解决方案，添加my_gui.place(relx=0.5, rely=0.5, anchor=CENTER)使次要的Canvas居中于主要的Canvas。你知道吗

要显示辅助Canvas，请执行以下操作：

my_gui = CellGrid(c, len(Map), len(Map[0]), 40, Map)
my_gui.place(relx=0.5, rely=0.5, anchor=CENTER)

问题4-在Cell::draw()函数中对词典使用的误解。你知道吗

The displayed error is "AttributeError: 'Cell' object has no attribute 'green'".

第一个单元格的值self.grid[0][0].value = 2，绘制单元格时，下面的self.fill = self.green生成错误。你知道吗

有三种可能性可以用来解决这个错误：

1. 用self.fill = '<color>'替换self.fill = self.<color>（7例）
2. 使用声明的dictionary colors，并用唯一的调用替换这7个case。你知道吗

字典的用法可以是（sol 2）：

if 0 <= self.value <= 6: # check if value in range of colors
    self.fill = Cell.colors[self.value]

而不是长if elif（sol 1）：

    if self.value == 0:
        self.fill = 'white' # Error: self.white
    elif self.value == 1:
        self.fill = 'black' # Error: self.black
    elif self.value == 2:
        self.fill = 'green' # Error: self.green
    elif self.value == 3:
        self.fill = 'red' # Error: self.red
    elif self.value == 4:
        self.fill = 'blue' # Error: self.blue
    elif self.value == 5:
        self.fill = 'gray' # Error: self.gray
    elif self.value == 6:
        self.fill = 'orange' # Error: self.orange