问题
I use Python 3 and I'm quite new to programming. I have written a code that's supposed to show a window in which you can move around two planets and see the gravitational force between them. Everything works excepted the label that's supposed to display the force. After multiple attempts and searches, I just can't find out how to update it every time a planet is being moved.
I guess my problem should be in the last line with :
lbl = Label(wind, bg = 'white', text = gravitation(oval1, oval2)).pack(padx=5, pady=5)
I've tried to use a StringVar and a textvariable parameter but I didn't really get the concepts of it.
Here is my code. I guess the answer is easy but I'm quite unexperienced.
from tkinter import *
import math
x, y = 135, 135
gravitation = 0
def gravitation (obj1,obj2):
a, b, c, d = can.coords (obj1)
e, f, g, h = can.coords (obj2)
dist = math.sqrt ((((a+c)/2)-((e+g)/2))**2+(((b+d)/2)-((f+h)/2))**2)
grav = 6.67384/dist
return grav
def move (ov, lr, tb): # function to move the ball
coo = can.coords(ov)
coo[0] = coo[0] + lr
coo[1] = coo[1] + tb
coo[2] = coo[0]+30
coo[3] = coo[1]+30
can.coords(ov, *coo)
def moveLeft ():
move(oval1, -10, 0)
def moveRight ():
move(oval1, 10, 0)
def moveTop ():
move(oval1, 0, -10)
def moveBottom ():
move(oval1, 0, 10)
def moveLeft2 ():
move(oval2, -10, 0)
def moveRight2 ():
move(oval2, 10, 0)
def moveTop2 ():
move(oval2, 0, -10)
def moveBottom2 ():
move(oval2, 0, 10)
##########MAIN############
wind = Tk() # Window and canvas
wind.title ("Move Da Ball")
can = Canvas (wind, width = 300, height = 300, bg = "light blue")
can.pack (side = LEFT,padx = 5, pady = 5)
Button(wind, text = 'Quit', command=wind.destroy).pack(padx = 5, pady = 5)
oval1 = can.create_oval(x,y,x+30,y+30,width=2,fill='orange') #Planet 1 moving etc
Button(wind, text = 'Left', command=moveLeft).pack(padx = 5, pady = 5)
Button(wind, text = 'Right', command=moveRight).pack(padx = 5, pady = 5)
Button(wind, text = 'Top', command=moveTop).pack(padx = 5, pady = 5)
Button(wind, text = 'Bottom', command=moveBottom).pack(padx = 5, pady = 5)
oval2 = can.create_oval(x+50,y+50,x+80,y+80,width=2,fill='orange') #Planet 2 moving etc
Button(wind, text = 'Left', command=moveLeft2).pack(padx = 5, pady = 5)
Button(wind, text = 'Right', command=moveRight2).pack(padx = 5, pady = 5)
Button(wind, text = 'Top', command=moveTop2).pack(padx = 5, pady = 5)
Button(wind, text = 'Bottom', command=moveBottom2).pack(padx = 5, pady = 5)
lbl = Label(wind, bg = 'white', text = gravitation(oval1, oval2)).pack(padx=5, pady=5)
wind.mainloop()
回答1:
Ok, there is a few things that need to be done. First, make your label like this:
lbl = Label(wind, bg = 'white', text = gravitation(oval1, oval2))
lbl.pack(padx=5, pady=5)
# Put this on its own line so that there are no errors since 'lbl' isn't defined yet
gravitation(oval1, oval2)
This will make lbl refer to the label like it should, not pack, which returns None.
Second, you will need to put this:
gravitation(oval1, oval2)
at the end of your move function so that, each time a movement in any direction takes place, it will update the label.
Third, instead of returning grav in gravitation, put this at the end:
lbl["text"] = grav
Now, each time gravitation is called, the label will be updated.
All in all, this should do what you want:
from tkinter import *
import math
x, y = 135, 135
def gravitation (obj1,obj2):
a, b, c, d = can.coords (obj1)
e, f, g, h = can.coords (obj2)
dist = math.sqrt ((((a+c)/2)-((e+g)/2))**2+(((b+d)/2)-((f+h)/2))**2)
grav = 6.67384/dist
##################
lbl["text"] = grav
##################
def move (ov, lr, tb):
coo = can.coords(ov)
coo[0] = coo[0] + lr
coo[1] = coo[1] + tb
coo[2] = coo[0]+30
coo[3] = coo[1]+30
can.coords(ov, *coo)
########################
gravitation(oval1, oval2)
########################
def moveLeft ():
move(oval1, -10, 0)
def moveRight ():
move(oval1, 10, 0)
def moveTop ():
move(oval1, 0, -10)
def moveBottom ():
move(oval1, 0, 10)
def moveLeft2 ():
move(oval2, -10, 0)
def moveRight2 ():
move(oval2, 10, 0)
def moveTop2 ():
move(oval2, 0, -10)
def moveBottom2 ():
move(oval2, 0, 10)
wind = Tk()
wind.title ("Move Da Ball")
can = Canvas (wind, width = 300, height = 300, bg = "light blue")
can.pack (side = LEFT,padx = 5, pady = 5)
Button(wind, text = 'Quit', command=wind.destroy).pack(padx = 5, pady = 5)
oval1 = can.create_oval(x,y,x+30,y+30,width=2,fill='orange') #Planet 1 moving etc
Button(wind, text = 'Left', command=moveLeft).pack(padx = 5, pady = 5)
Button(wind, text = 'Right', command=moveRight).pack(padx = 5, pady = 5)
Button(wind, text = 'Top', command=moveTop).pack(padx = 5, pady = 5)
Button(wind, text = 'Bottom', command=moveBottom).pack(padx = 5, pady = 5)
oval2 = can.create_oval(x+50,y+50,x+80,y+80,width=2,fill='orange') #Planet 2 moving etc
Button(wind, text = 'Left', command=moveLeft2).pack(padx = 5, pady = 5)
Button(wind, text = 'Right', command=moveRight2).pack(padx = 5, pady = 5)
Button(wind, text = 'Top', command=moveTop2).pack(padx = 5, pady = 5)
Button(wind, text = 'Bottom', command=moveBottom2).pack(padx = 5, pady = 5)
###############################
lbl = Label(wind, bg = 'white')
lbl.pack(padx=5, pady=5)
gravitation(oval1, oval2)
##############################
wind.mainloop()
I put comment boxes around everything I changed. Also, I removed gravitation = 0 at the start since defining the gravitation function will overwrite this. Hope this helps!
来源：https://stackoverflow.com/questions/18576978/update-tkinter-label