Tkinter在按下按钮时不会改变图像

Question

I have loaded an image to tkinter label and that image is diplayed in that label.When i press the button i need to change that image.When the button is pressed older image is gone but the new image is not displayed My code is

import Tkinter as tk
from PIL import Image, ImageTk
root = tk.Tk()

def change_pic(labelname):
 photo1 = ImageTk.PhotoImage(Image.open("demo.jpg"))
 labelname.configure(image=photo1)
 print "updated"

vlabel=tk.Label(root)
photo = ImageTk.PhotoImage(Image.open('cardframe.jpg'))
vlabel.configure(image=photo)
vlabel.pack()
b2=tk.Button(root,text="Capture",command=lambda:change_pic(vlabel))
b2.pack()
root.mainloop()

Answer 1

In def change_pic(labelname) , you need to add labelname.photo = photo1 to make sure photo1 not being garbage collected.

def change_pic(labelname):
    photo1 = ImageTk.PhotoImage(Image.open("demo.jpg"))
    labelname.configure(image=photo1)
    labelname.photo = photo1
    print "updated"

PS Looks like both labelname.photo = photo1 and labelname.image = photo1 work.

Check this out for more details: http://effbot.org/tkinterbook/label.htm

You can use the label to display PhotoImage and BitmapImage objects. When doing this, make sure you keep a reference to the image object, to prevent it from being garbage collected by Python's memory allocator. You can use a global variable or an instance attribute, or easier, just add an attribute to the widget instance.

Answer 2

The following edits were made:

1. I have organised your code layout and simplified its syntax where possible. These are to make your code easier to read.
2. Commonly we make the PIL objects a subset/children of tk. So long it is a part of root (ie it is a child of the root or any of its child widgets), your PIL objects will work.

Your working code is shown below:

import Tkinter as tk
from PIL import Image, ImageTk

def change_pic():
    vlabel.configure(image=root.photo1)
    print "updated"

root = tk.Tk()

photo = 'cardframe.jpg'
photo1 = "demo.jpg"
root.photo = ImageTk.PhotoImage(Image.open(photo))
root.photo1 = ImageTk.PhotoImage(Image.open(photo1))

vlabel=tk.Label(root,image=root.photo)
vlabel.pack()

b2=tk.Button(root,text="Capture",command=change_pic)
b2.pack()

root.mainloop()

Answer 3

I got it working with one more line of code:

import tkinter as tk                        # I am using python 3 on windows so the tkinter is lowercased
from PIL import Image, ImageTk
root = tk.Tk()

def change_pic(labelname):
    global photo1                           # This is the only new line you need, I believe
    photo1 = ImageTk.PhotoImage(Image.open("demo.jpg"))
    labelname.configure(image=photo1)
    print("updated")                        # Again I'm using python 3 on windows so syntax may differ.
    root.update()                           # You don't need this statement in this case, but it never hurts

vlabel=tk.Label(root)
photo = ImageTk.PhotoImage(Image.open('cardframe.jpg'))
vlabel.configure(image=photo)
vlabel.pack()
b2=tk.Button(root,text="Capture",command=lambda:change_pic(vlabel))
b2.pack()
root.mainloop()

I believe that the code changes the image locally, so the global statement will change it on the project scope.