在GUI中运行sql查询时，ttk进度栏停止

Question

I'm building a GUI which at some point(s) will query a SQL database. Whilst the query is running, I wanted to show the user an indeterminate progress bar (ttk) which would indicate this. See below for simple example.

from Function_Sheet import *
from Tkinter import *
import ttk
root = Tk()

s = ttk.Style()
s.theme_use('clam')
s.configure('red.Horizontal.TProgressbar', foreground='red', background='red')
mpb2 = ttk.Progressbar(root,style='red.Horizontal.TProgressbar', orient ='horizontal', length = 200, mode ='indeterminate')
mpb2.pack()
mpb2.start(1)
print 'query not done'
cursor = SolvittConnect(<SQL HERE>)
print 'query done'
root.mainloop()

Unfortunatley the query seems to run even before the root window is loaded.

How can I show the moving progress bar WHILST the query is being executed?

Any feedback would be appreciated.

Answer 1

For tkinter to draw anything, it must be in the mainloop. The mainloop is exactly as it sounds- an infinite loop which handles events. As such, commands after the mainloop are not done until the mainloop completes.

To solve your issue, you need to setup the SQL query to happen in the mainloop while the GUI updates. Do this by setting up an after call- it will be a lambda probably, so this is a good time to swap to classes, since they allow you to call a method from an after and that method can set a class variable

class ...
    ...
    def __init__(self):
        root=Tk()
        ...
        mpb2.start(1)
        root.after(1000, # in milliseconds
                   lambda *e: self.connect())   
        root.mainloop()
        ...
    def connect(self):
        print "querying"
        self.cursor = SolvittConnect(<SQL>)
        print "query complete"

Note that your SolvittConnect will probably stop the GUI from updating- look into throwing that to a thread or a worker pool, since the GUI can't update while python is executing a function (unless there are explicit calls during execution, but SolvittConnect doesn't explicitly tell the GUI to update while it tries to connect)