为什么我的Tkinter画布显示？

Question

I am trying to produce a star algorithm using Tkinter 2d graphical user interface. I have modified the following code having found it originally on here:

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()

But when I go to run it, nothing displays.

Answer 1

A lot of small and not-small misunderstandings are blocking the display of the star algorithm .

Problem 1 - incomplete calling main() function.

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

Just add the following code after the def main() function:

if __name__ == '__main__':
    main()

Problem 2 - typo and missing pack() to the main Canvas display.

Because the tk symbol is not defined, the main Canvas shall be declared as follow:

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

Instead of:

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

And after the magic missing call is pack() :

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

Problem 3 - missing call to the secondary Canvas display.

As for the main Canvas , it was missing the call of pack() , two possibilities could be used to display the secondary Canvas .

1. Add my_gui.pack() to fit the main Canvas to the size of the secondary Canvas ,
2. Or my preferred solution, add my_gui.place(relx=0.5, rely=0.5, anchor=CENTER) to center the secondary Canvas to the main Canvas .

To display the secondary Canvas :

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

Problem 4 - misunderstanding of dictionary use in the Cell::draw() function.

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

The value of the first cell self.grid[0][0].value = 2 and when drawing the cell, the following self.fill = self.green generates the error.

Three possibilities could be used to solve that error:

1. Replace the self.fill = self.<color> (7 cases) by self.fill = '<color>' ,
2. Use the declared dictionary colors and replace the 7 cases by a unique call.

The use of dictionary could be (sol 2):

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

Instead of the long 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