[Tkinter-discuss] Kind of the old intercept the Entry() tab key question

[Bob Greschke]

On Feb 25, 2010, at 03:52, Michael Lange wrote:

> Hi Bob,
> 
> On Wed, 24 Feb 2010 17:15:34 -0700
> Bob Greschke <bob at passcal.nmt.edu> wrote:
> 
>> I know this must have been handled before (but I can find no evidence
>> of it), but what I want to do is have an entry field for filespecs
>> (path+filename) that is on the same 'form' with other entry fields
>> and I want the user to be able to use the Tab key to get to the field
>> (so takefocus needs to be 1).
>> 
>> When the field has the focus if what is in the field (i.e. the
>> StringVar) does not match any filename (or path) when the Tab key is
>> pressed I just want the program to beep and the cursor to stay in the
>> field.
>> 
>> If what is in there can be completed to match a filename (or path)
>> then the contents gets completed when the Tab is pressed and the
>> cursor stays in the field.
>> 
>> If what is in the field already matches a filename (or path) then the
>> Tab key press goes on to the next field as it usually would for other
>> Entry fields.
>> 
>> Is this possible?  At this point I'm still not having much luck just
>> getting the cursor to stay put after a Tab press, and using return
>> "break" in the <Tab> handler doesn't seem to be doing anything (I've
>> only ever gotten the "break" thing to work once a long time ago, but
>> then didn't use it, and I can't remember how I got it to work).
>> 
> 
> Maybe you should rather use the Focus-Out event:
> 
> import Tkinter
> root = Tkinter.Tk()
> e = Tkinter.Entry(root)
> e.pack(padx=100, pady=50)
> 
> def focus_out(event):
>    if e.get() != 'foo':
>        e.bell()
>        e.focus_set()
> e.bind('<FocusOut>', focus_out)
> 
> b = Tkinter.Button(root, text='quit', command=root.destroy)
> b.pack(padx=100, pady=50)
> b.focus_set()
> root.mainloop()
> 
> Alternatively you can try the Entry's validatecommand, however this is
> a little tricky, because you need percent substitutions:
> 
> import Tkinter
> root = Tkinter.Tk()
> e = Tkinter.Entry(root)
> e.pack(padx=100, pady=50)
> 
> def validate(s):
>    if s != 'foo':
>        return 0
>    return 1
> 
> def invcmd():
>    e.bell()
>    e.focus_set()
> 
> vcmd = (e.register(validate), '%P')
> e.configure(vcmd=vcmd, validate='focusout', invcmd=invcmd)
> 
> b = Tkinter.Button(root, text='quit', command=root.destroy)
> b.pack(padx=100, pady=50)
> b.focus_set()
> root.mainloop()
> 
> 
> I hope this helps!
> 
> Michael

Nice.  They did help, thanks!  After sleeping on it I think I'm going to go with a completely non-standard 'use the Return key' for doing this, instead of the Tab key.  These are just in-house, only used by scientist-types programs, so not using the Tab key won't be a big problem.  On top of that just tabbing through one of these field could potentially result in making the handler collect and look through literally 1000's (or 10's of 1000's) of file names, and that could cause a significant pause, so you'll really only want it to happen when the user really asks for it.  I didn't know about the validation stuff for regular Entry fields.  I only knew about that for PMW entry fields.  Great!

Thanks!

Bob