[Tkinter] Validating and modifying a Spinbox

[pfdjhfuys]

Below is a code snippet of a program that uses the SpinBox control. I want to the control to allow numbers between 1 and 100 as set in from_ and to.

I borrowed some code to validate the control when it focuses out. Problem is that I am not able to reset the control. Returning false does not seem to have any impact on the control.

Below I placed a short video in which I write letters into the control. I detect the error but am not able to reset it.

Thanks.

from tkinter import *


class GUI:
    """
    Handles the GUI interface
    """   
    
    def __init__(self):
        """_summary_
        """        
        # root window
        self.root = Tk()
        self.root.title("Password Generator")
        self.root.geometry("800x300")
        self.root.resizable(width=FALSE, height=FALSE)

        # registering validation command
        vldt_ifnum_cmd = (self.root.register(self.ValidateIfNum),'%P', '%W')
 
        # pass length information
        self.passTitle = Label(self.root, text = "Passowrd Length: ").grid(row=0, column=0, padx=5, pady=5, sticky=E)
        self.passLen = IntVar(value=20) 
        self.passLenSb = Spinbox(
            self.root, 
            from_=1, 
            to=100, 
            textvariable=self.passLen, 
            width=10, 
            justify=CENTER, 
            bd=3, 
            validate='focusout', 
            validatecommand=vldt_ifnum_cmd
            ).grid(row=0, column=1, padx=5, pady=5)

        self.Note = Label(self.root, text = "Press TAB to lose focus on Spinbox").grid(row=8, column=2)
      
        
    def ValidateIfNum(self, user_input, widget_name):
        # disallow anything but numbers in the input
        valid = user_input.isdigit()
        # now that we've ensured the input is only integers, range checking!
        if valid:
            # get minimum and maximum values of the widget to be validated
            minval = int(self.root.nametowidget(widget_name).config('from')[4])
            maxval = int(self.root.nametowidget(widget_name).config('to')[4])
            # check if it's in range
            if int(user_input) not in range (minval, maxval):
                valid = False
        if not valid:
            # reset the value to the original 
            self.passLen = IntVar(value=20) 
        return valid

[pfdjhfuys]

After going through the documentation Tcl8.6.13/Tk8.6.13 Documentation > Tk Commands > spinbox I found out that:

In general, the -textvariable and -validatecommand can be dangerous to mix. Any problems have been overcome so that using the -validatecommand will not interfere with the traditional behavior of the spinbox widget. Using the -textvariable for read-only purposes will never cause problems. The danger comes when you try set the -textvariable to something that the -validatecommand would not accept, which causes -validate to become none (the -invalidcommand will not be triggered). The same happens when an error occurs evaluating the -validatecommand.

Primarily, an error will occur when the -validatecommand or -invalidcommand encounters an error in its script while evaluating or -validatecommand does not return a valid Tcl boolean value. The -validate option will also set itself to none when you edit the spinbox widget from within either the -validatecommand or the -invalidcommand. Such editions will override the one that was being validated. If you wish to edit the value of the widget during validation and still have the -validate option set, you should include the command

I was overthinking the problem.

The code below worked:

  def ValidateIfNum(self, user_input, widget_name):
        """
        Args:
            user_input (IntVal): The value typed into the spinbox
            widget_name (): The widget name

        Returns:
            Boolean: Whether the value is valid
        """
        
        valid = user_input.isdigit()
        # now that we've ensured the input is only integers, range checking!
        if valid:
            # get minimum and maximum values of the widget to be validated
            minval = int(self.root.nametowidget(widget_name).config('from')[4])
            maxval = int(self.root.nametowidget(widget_name).config('to')[4])
            # check if it's in range
            if int(user_input) not in range (minval, maxval):
                valid = False
            
        return valid

[pfdjhfuys]

Hi,

Would like to share a link to the complete solution: PasswordGeneratorGUI.

The SpinBox control proved particularly challenging to fine tune it to where I wanted to get it.

The up and down arrows always worked as expected but I was never able to easily manage if someone typed in an invalid string in the box. I was expecting that if someone typed in, dd, I could capture an onChange or onFocusLost event out of the box and take corrective action.

I found that pressing Tab did not cause the SpinBox to loose focus (even though the cursor would jump).

The lines below seem to have done the trick.

        self.root.bind('<Return>', self.reset_focus)
        self.root.bind('<Tab>', self.reset_focus)

Still not sure whether it could have been achieved without the need to code them in (they are built into the tool).

---

Another observation is that the name of the spinbox I define in python is different from that in Tcl/tk (widget) and I can't figure out how to get from the python name to the internal equivalent. Can one get to this via

(self.root.register(self.ValidateIfNum),'%P', '[b]%W[/b]')

?

With one spinbox the solution is manageable.

Thanks for any comments