Python Tkinter how to hide a widget without removing it - python

I know similar things have been asked a lot, but I've tried to figure this out for two hours now and I'm not getting anywhere. I want to have a button in a Tkinter window that is only visible on mouseover. So far I failed at making the button invisible in the first place (I'm familiar with events and stuff, that's not what this question is about) pack_forget() won't work, because I want the widget to stay in place. I'd like some way to do it like I indicated in the code below:
import tkinter as tki
class MyApp(object):
def __init__(self, root_win):
self.root_win = root_win
self.create_widgets()
def create_widgets(self):
self.frame1 = tki.Frame(self.root_win)
self.frame1.pack()
self.btn1 = tki.Button(self.frame1, text='I\'m a button')
self.btn1.pack()
self.btn1.visible=False #This doesnt't work
def main():
root_win = tki.Tk()
my_app = MyApp(root_win)
root_win.mainloop()
if __name__ == '__main__':
main()
Is there any way to set the visibility of widgets directly? If not, what other options are there?

Use grid as geometry manager and use:
self.btn1.grid_remove()
which will remember its place.

You can try using event to call function.
If "Enter" occurs for button then call a function that calls pack()
and if "Leave" occurs for button then call a function that calls pack_forget().
Check this link for event description:List of All Tkinter Events
If you wish your button to stay at a defined place then you can use place(x,y) instead of pack()

Related

How to sound a bell when the user clicks outside a modal window?

The situation is simple. I have a main window with a Help - About menu.
When this menu item is clicked, a modal window is opened (let's say it's an About-window).
With self.grab_set() I disabled the main-window (although the modal window does flicker when you click the main title bar).
So far, so good.
Here is the question: I really like to sound a bell when the user clicks outside the modal window on the main window.
This is what I could find about grab_set(), really not that much:
[effbot] ...a method called grab_set, which makes sure that no mouse or keyboard
events are sent to the wrong window.
[effbot] Routes all events for this application to this widget.
[kite.com] A grab directs all events to this and descendant widgets in the application.
[google books] grab_set() ensures that all of the application's events are sent to w until a corresponding call is made to grab_release ([Me:] or till the window is destroyed?)
I'm not quite sure how to understand this: does it mean you can handle an event on the main window within the modal window (like sounding my bell)?
So I tried things like:
self.bind('<Button-1>', self.bell) Exception in Tkinter callback: _tkinter.TclError: bad window path name
parent.bind('<Button-1>', self.bell) Nothing happens
So, how to sound a bell like when clicked outside the modal window on the main window, like in so many other applications?
Derived questions:
Is it still possible to cature events from the main window after using
grab_set for the modal window?
Is there a way to prevent the flickering?
I really like to understand this mysterious grab_set() method.
Stripped code:
import tkinter as tk
class About(tk.Toplevel):
def __init__(self, parent):
tk.Toplevel.__init__(self, parent)
self.geometry('200x150')
#--- OK button
btn_ok = tk.Button(self, text='OK', command=self.destroy) # destroy with OK
btn_ok.pack(side=tk.TOP)
btn_ok.focus() # destroy with spacebar
#--- Make window modal
self.grab_set()
# self.wait_window() # is this necessary in this case?
# self.bind('<Button-1>', self.bell) ??? The question
class MenuBar(tk.Menu):
def __init__(self, parent):
tk.Menu.__init__(self)
helpmenu = tk.Menu(self, tearoff=0)
helpmenu.add_command(label='About', command=lambda: About(parent))
self.add_cascade(label='Help', menu=helpmenu)
class MainApp():
def __init__(self, parent):
parent.configure(background='#000000')
parent.geometry('800x600')
menubar = MenuBar(parent)
parent.configure(menu=menubar)
if __name__ == '__main__':
root = tk.Tk()
MainApp(root)
root.mainloop()
When you set a grab, all button clicks will go to the window with the grab. You capture them the way you capture any other event. In the case of a button click you do that by binding a function to <1>.
It's important to know that a binding on a root window or a Toplevel window will apply to all widgets in that window. For example, binding to self in your code will fire even when you click on the "Ok" button. Therefore, the callback should probably only do work when the widget associated with the event is the same as the toplevel.
Example:
class About(tk.Toplevel):
def __init__(self, parent):
...
self.bind("<1>", self.capture_click)
...
def capture_click(self, event):
if event.widget == self:
<your logic here>
In the case of wanting to know if the user clicked outside the window, you can use the coordinates of the event object to compare against the window to see if the click is inside or outside.
def on_click(self, event):
if event.widget == self:
if (event.x < 0 or event.x > self.winfo_width() or
event.y < 0 or event.y > self.winfo_height()):
self.bell()
I found a second solution. Though my question was explicitly about using grab_set(), this method does the same for me: making the window as modal as possible and sound a bell.
Instead of using self.grab(), you can also disable the parent window:
parent.attributes('-disabled', True)
Of course it needs to be enabled again when the OK button is clicked (and when the windows is closed with the [X] close control. However, my original About-window has no window decoration). The command for the OK-button becomes:
btn_ok = tk.Button(self, text='OK', command=lambda: self.closeme(parent))
...which calls the closeme function:
def closeme(self, parent):
parent.attributes('-disabled', False)
self.destroy()
The bell sounds automatically when clicking a disabled window.
Method 1: Keeps you in full control of the main window but does not 'freeze' the main window: you can still move it around.
Method 2: Completely freezes the main window, but if it happens to be (partially) covered by another window (not of this application), then you can only bring back to top using Alt+Tab (windows).
I'm sure I will use both techniques in the future depending on my needs.

Delete all from TkInter Canvas and put new items while in mainloop

The goal is to achieve different "screens" in TkInter and change between them. The easiest to imagine this is to think of a mobile app, where one clicks on the icon, for example "Add new", and new screen opens. The application has total 7 screens and it should be able to change screens according to user actions.
Setup is on Raspberry Pi with LCD+touchscreen attached. I am using tkinter in Python3. Canvas is used to show elements on the screen.
Since I am coming from embedded hardware world and have very little experience in Python, and generally high-level languages, I approached this with switch-case logic. In Python this is if-elif-elif...
I have tried various things:
Making global canvas object. Having a variable programState which determines which screen is currently shown. This obviously didn't work because it would just run once and get stuck at the mainloop below.
from tkinter import *
import time
root = Tk()
programState = 0
canvas = Canvas(width=320, height=480, bg='black')
canvas.pack(expand=YES, fill=BOTH)
if(programState == 0):
backgroundImage = PhotoImage(file="image.gif")
canvas.create_image(0,0, image=backgroundImage, anchor=NW);
time.sleep(2)
canvas.delete(ALL) #delete all objects from canvas
programState = 1
elif(programState == 1):
....
....
....
root.mainloop()
Using root.after function but this failed and wouldn't show anything on the screen, it would only create canvas. I probably didn't use it at the right place.
Trying making another thread for changing screens, just to test threading option. It gets stuck at first image and never moves to second one.
from tkinter import *
from threading import Thread
from time import sleep
def threadFun():
while True:
backgroundImage = PhotoImage(file="image1.gif")
backgroundImage2 = PhotoImage(file="image2.gif")
canvas.create_image(0,0,image=backgroundImage, anchor=NW)
sleep(2)
canvas.delete(ALL)
canvas.create_image(0,0,image=backgroundImage2, anchor=NW)
root = Tk()
canvas = Canvas(width=320, height=480, bg='black')
canvas.pack(expand=YES, fill=BOTH)
# daemon=True kills the thread when you close the GUI, otherwise it would continue to run and raise an error.
Thread(target=threadFun, daemon=True).start()
root.mainloop()
I expect this app could change screens using a special thread which would call a function which redraws elements on the canvas, but this has been failing so far. As much as I understand now, threads might be the best option. They are closest to my way of thinking with infinite loop (while True) and closest to my logic.
What are options here? How deleting whole screen and redrawing it (what I call making a new "screen") can be achieved?
Tkinter, like most GUI toolkits, is event driven. You simply need to create a function that deletes the old screen and creates the new, and then does this in response to an event (button click, timer, whatever).
Using your first canvas example
In your first example you want to automatically switch pages after two seconds. That can be done by using after to schedule a function to run after the timeout. Then it's just a matter of moving your redraw logic into a function.
For example:
def set_programState(new_state):
global programState
programState = new_state
refresh()
def refresh():
canvas.delete("all")
if(programState == 0):
backgroundImage = PhotoImage(file="image.gif")
canvas.create_image(0,0, image=backgroundImage, anchor=NW);
canvas.after(2000, set_programState, 1)
elif(programState == 1):
...
Using python objects
Arguably a better solution is to make each page be a class based off of a widget. Doing so makes it easy to add or remove everything at once by adding or removing that one widget (because destroying a widget also destroys all of its children)
Then it's just a matter of deleting the old object and instantiating the new. You can create a mapping of state number to class name if you like the state-driven concept, and use that mapping to determine which class to instantiate.
For example:
class ThisPage(tk.Frame):
def __init__(self):
<code to create everything for this page>
class ThatPage(tk.Frame):
def __init__(self):
<code to create everything for this page>
page_map = {0: ThisPage, 1: ThatPage}
current_page = None
...
def refresh():
global current_page
if current_page:
current_page.destroy()
new_page_class = page_map[programstate]
current_page = new_page_class()
current_page.pack(fill="both", expand=True)
The above code is somewhat ham-fisted, but hopefully it illustrates the basic technique.
Just like with the first example, you can call update() from any sort of event: a button click, a timer, or any other sort of event supported by tkinter. For example, to bind the escape key to always take you to the initial state you could do something like this:
def reset_state(event):
global programState
programState = 0
refresh()
root.bind("<Escape>", reset_state)

Multiple tkinter windows look different when closing and reopening window

I got the following code from a tutorial. I then modified main() so that two windows are created as seperate threads. When I run it, only one window is created. Then when I press the Quit button in that window, a second window appears. In this new window the button has a different look than the first one (a look which I like better) and then if I press either of the two Quit buttons, both windows close and the program exits.
Why does the second window not appear until the first Quit button is pressed, and why does it look different when it does appear?
EDIT: This happens when no threads are used as well, where only one window is created at a time.
EDIT: This is a screenshot of the two windows that are created. The one on the left is created with the program is run, the one on the right is created after clicking the "Quit" button on the first.
from Tkinter import Tk, BOTH
from ttk import Frame, Button, Style
class Example(Frame):
def __init__(self, parent):
Frame.__init__(self, parent)
self.parent = parent
self.initUI()
def initUI(self):
self.parent.title("Quit button")
self.style = Style()
self.style.theme_use("default")
self.pack(fill=BOTH, expand=1)
quitButton = Button(self, text="Quit",
command=self.quit)
quitButton.place(x=50, y=50)
from threading import Thread
def main():
for i in range(2):
root = Tk()
root.geometry("250x150+300+300")
app = Example(root)
Thread(target=root.mainloop()).start()
if __name__ == '__main__':
main()
You cannot use tkinter this way. Tkinter isn't thread safe, you can only ever access tk widgets and commands except from the thread that created the root window.
As for one window only showing after the other is destroyed even without threading, it's hard to say since you don't show the code. If you're creating more than one instance of Tk, and calling mainloop more than once, that's the problem. Tkinter is designed to work when you create precisely one instance of Tk, and call mainloop precisely once.
If you want more than one window, create a single instance of Tk for the first window, and instances of Toplevel for additional windows.

How to test to see if a top-level window is open?

I'm feeling somewhat like Python programming may not be my thing....
I have created a tkinter GUI that uses a button callback to open another window (other searches say this window should be a top-level window) and it works pretty good, how-ever each time the button is pressed it opens another identical (as far as I can tell) window.
Question: how can I test to see if a window (opened with the button) already exists and thus prevent duplicates from being generated???
NOTE: I am not (yet) a OOP programmer so please avoid that paradigm if possible...
regards,
Bill W.
I am not (yet) a OOP programmer so please avoid that paradigm if possible...
Sooner or later, you'll have to understand object-oriented programming if you want to program in Python successfully. The alternative (global variables and functions everywhere) is not definitely a good approach. Even Tkinter has lots of classes with its respective methods, so it looks like it is necessary for your purpose.
Back to your question, a solution could be setting the Toplevel window as an attribute of a class where you wrap all your application, and only open a new window if this attribute is None. To set this attribute to None when you close the window, you can use the protocol method to set a callback.
This is a small working example where you can see how it would work:
import Tkinter as tk
class App(tk.Tk):
def __init__(self):
tk.Tk.__init__(self)
self.button = tk.Button(self, text="Open a new window", command=self.openwindow)
self.button.pack()
self.toplevel = None
def openwindow(self):
if self.toplevel is None:
self.toplevel = tk.Toplevel(self)
self.toplevel.protocol('WM_DELETE_WINDOW', self.removewindow)
def removewindow(self):
self.toplevel.destroy()
self.toplevel = None
app = App()
app.mainloop()
You can use this method winfo_exists() to check if the window exists.
if the return value is 0, it means the window doesn't exist.
if the return value is 1, it means the window exists.
Sample Code...
from tkinter import *
mainWindow = Tk()
mainWindow.title("This is main Window")
# create a top-level window
newWindow = Toplevel(mainWindow)
newWindow.title("This is Toplevel window")
print("Before destroying window = " + str(newWindow.winfo_exists()))
newWindow.destroy()
print("After destroying window = " + str(newWindow.winfo_exists()))
mainloop()
Output is...
# Before destroying window = 1
# After destroying window = 0

tk destroy() and grid_forget() don't always work

i'm hoping anyone can help me out here. i'm having an issue with a tkinter gui i built. the issue only happens in windows. My GUI creates a results frame with some labels in it, when it's time to calculate something else, the user clicks on the "newPort" button and that button is supposed to remove the results frame and set to False some instance attributes internal to the calculation. The issue i'm having, which is apparent only in windows is that sometimes the results frame, and its descendant labels don't disappear every time. Sometimes they do, sometimes they don't. The instance variable is correctly set to False but the widgets are still visible on the main GUI. The GUI also contains a couple checkboxes and radiobuttons but they don't impact the creation of the results frame nor its expected destruction. I have not been able to pin point a pattern of actions the user takes before clicking on the newPort button which causes the frame and labels to not get destroyed. This happens when i freeze my app with py2exe, as well as running the app from the python interpreter within the eclipse IDE. I have not tried running the app from the python interpreter directly (i.e. without the IDE) and this problem does not happen on my Mac when i run the app using the eclipse python interpreter. Thanks very much all! My code looks like this:
import Tkinter as TK
class widget(object):
def __init__(self,parent=None):
self.parent = TK.Frame(parent)
self.parent.grid()
self.frame = TK.Frame(self.parent)
self.frame.grid()
newLedger = TK.Button(self.parent,command=self.newPort).grid()
self.calcButton = TK.Button(self.frame,command=self.showResults)
self.calcButton.grid()
self.calcVariable = True
def newPort(self):
self.calcVariable = False
try:
self.second.grid_forget()
self.first.grid_forget()
self.resultsFrame.grid_forget()
self.second.destroy()
self.first.destroy()
self.resultsFrame.destroy()
except:
raise
self.frame.update_idletasks()
def showResults(self):
self.resultsFrame = TK.Frame(self.frame)
self.resultsFrame.grid()
self.first = TK.Label(self.resultsFrame,text='first')
self.first.grid()
self.second = TK.Label(self.resultsFrame,text='second')
self.second.grid()
if __name__ == '__main__':
root = TK.Tk()
obj = widget(root)
root.mainloop()
You don't need to destroy or call grid_forget on the labels, and you don't need to call grid_forget on the resultsFrame; when you destroy the resultsFrame it will cause all off its children to be destroyed, and when these widgets are destroyed they will no longer be managed by grid.
The only way I can get widgets to not be destroyed is if I click on the "calc" button twice in a row without clicking on the "new" button in-between. I'm doing this by running your program from the command line.

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