在 canvas python 上移動 object

Question

我想讓一個小方塊每 3 秒向左移動 10 個像素，我的代碼如下。 我不確定為什么它只移動一次。 一些幫助將不勝感激！

import tkinter as tk
import time
 
root = tk.Tk()
 
WIDTH = HEIGHT = 400
 
x1 = y1 = WIDTH / 2
 
canvas = tk.Canvas(root, width=WIDTH, height=HEIGHT)
canvas.pack()
 
c1 = canvas.create_rectangle(x1, y1, x1 + 10, y1 + 10)
c2 = canvas.create_rectangle(x1, y1, x1 + 10, y1 + 10)
 
 
def draw_rect():
    global c2
    canvas.delete(c2)
    c2 = canvas.create_rectangle(x1, y1, x1 + 10, y1 + 10, fill="green")
 
 
def del_rect():
    canvas.delete(c1)
    #canvas.create_rectangle(x1, y1, x1 + 10, y1 + 10, fill="white", opacity=0.5)

while 1:
    root.update()
    time.sleep(3)
    del_rect()
    x1 -= 10    
    draw_rect()
    root.mainloop()

Answer 1

mainloop()運行循環，直到你關閉 window - 所以它阻塞所有循環並且它只執行一次並且它只移動一次矩形。 在您的版本中，您應該刪除mainloop()並且它不會阻止它 - 因為您在循環中使用update()所以它會正確運行。

但你可以用不同的方式做到這一點。

您可以使用root.after(3000, draw_rect) ) 在 3 秒后執行draw_rect() 。 並且draw_rect()應該再次運行root.after(3000, draw_rect)以在另外 3 秒后再次運行它 - 這樣它將循環並且不會被mainloop()阻塞（ mainloop()將每 3 秒運行一次draw_rect() )

Canvas有 function move(object, dx, dy)所以你不必刪除矩形並再次創建它。

我使用300ms來更快地運行它。

import tkinter as tk

# --- constants --- (PEP8: UPPER_CASE_NAMES)

WIDTH = 400
HEIGHT = 400

# --- functions ---

def move_rect():
    canvas.move(c1, -10, 0)  # move left
    canvas.move(c2, 10, 0)   # move right
    
    # run again after 300ms
    root.after(300, move_rect)  # 300ms = 0.3s  # I use smaller value to make it faster

# --- main ---

x1 = y1 = WIDTH / 2
 
root = tk.Tk()

canvas = tk.Canvas(root, width=WIDTH, height=HEIGHT)
canvas.pack()
 
c1 = canvas.create_rectangle(x1, y1, x1 + 10, y1 + 10, fill="green")
c2 = canvas.create_rectangle(x1, y1, x1 + 10, y1 + 10, fill="red")

# run first time after 300ms
root.after(300, move_rect)  # 300ms = 0.3s  # I use smaller value to make it faster
 
root.mainloop()

---

PEP 8 -- Python 代碼的樣式指南

---

編輯：

當矩形靠近邊界時，使用變量speed1 ， speed2改變方向的版本。

import tkinter as tk

# --- constants --- (PEP8: UPPER_CASE_NAMES)

WIDTH = 400
HEIGHT = 400

# --- functions ---

def move_rect():
    global speed1
    global speed2
    
    #x1, y1, x2, y2 = canvas.coords(c1)
    pos = canvas.coords(c1)
    if speed1 < 0 :
        if pos[0] < 10:
            speed1 = -speed1
    else:
        if pos[2] > WIDTH-10:
            speed1 = -speed1
        
    #x1, y1, x2, y2 = canvas.coords(c2)
    pos = canvas.coords(c2)
    if speed2 < 0:
        if pos[0] < 10:
           speed2 = -speed2
    else:
        if pos[2] > WIDTH-10:
            speed2 = -speed2
        
    canvas.move(c1, speed1, 0)  # move left    
    canvas.move(c2, speed2, 0)  # move right
    
    # run again after 30ms
    root.after(30, move_rect)  # 30ms = 0.03s  - I uses smaller value to make it faster

# --- main ---

x1 = y1 = WIDTH / 2

speed1 = -10
speed2 = +10

root = tk.Tk()

canvas = tk.Canvas(root, width=WIDTH, height=HEIGHT)
canvas.pack()
 
print(dir(canvas)) 
c1 = canvas.create_rectangle(x1, y1, x1 + 10, y1 + 10, fill="green")
c2 = canvas.create_rectangle(x1, y1, x1 + 10, y1 + 10, fill="red")

# run first time after 300ms
root.after(300, move_rect)  # 300ms = 0.3s  - I uses smaller value to make it faster
 
root.mainloop()