StringVar变量不返回值

Question

在以下代码段中，我希望我的TKINTER程序从文本字段中获取值并将其存储在变量中。但是问题在于，存储的值是默认值stringvar（）变量值（''），而不是文本字段中的值。我尝试使用get（）方法而没有成功。

代码： -

    var_stor = [hpw_cb.cget(key='onvalue'), mil_cb.cget(key='onvalue')]
    car1_hpw = StringVar()
    car1_mil = StringVar()

    car1_val = []
    # For Car1 Window
    hpw_lb_c1 = Label(c1,   text="Horsepower")
    hpw_ifl_c1 = Entry(c1, textvariable=car1_hpw)
    mil_lb_c1 = Label(c1, text="Mileage")
    mil_ifl_c1 = Entry(c1, textvariable=car1_mil)
    c1_ftr_grp = [hpw_lb_c1, hpw_ifl_c1, mil_lb_c1, mil_ifl_c1]
    for i in var_stor:
        if i == "Horsepower":
            c1_ftr_grp[0].pack(padx=12, pady=20)
            c1_ftr_grp[1].pack(padx=12, pady=20)
            car1_hpw_str = car1_hpw.get()
            car1_val.append(car1_hpw_str)
            print(car1_hpw.get())
        elif i == "Mileage":
            c1_ftr_grp[2].pack(padx=12, pady=20)
            c1_ftr_grp[3].pack(padx=12, pady=20)
            car1_mil_str = car1_mil.get()
            car1_val.append(car1_mil_str)
            print(car1_mil.get())
    print(car1_val)

问题变量是： - car1_hpw，car1_mil

如何纠正此问题？

Answer 1

它无法立即获得价值。您需要为其使用一个按钮。将按钮调用一个函数，然后使用该值，然后使用它做事。我还看到您正在使用条目。条目不需要StringVar（）来获取值。它只需要存储在变量中的对象的名称。

Answer 2

您可以从许多不同的事件触发功能。这取决于需要什么。下面是3种可能的方法，但仅是一个样本。

import tkinter as tk
from tkinter import ttk 

root = tk.Tk()

focus_v = tk.StringVar()
trace_v = tk.StringVar()
wait_v  = tk.StringVar() 

fmt = { 'padx': 5, 'pady': 5 }

r = 0
ttk.Label( root, text = 'Act on losing focus' ).grid( row = r, column = 0, **fmt )
ent_focus = ttk.Entry( root, textvariable = focus_v )
ent_focus.grid( row = r, column = 1, **fmt )
result_f = ttk.Label( root, text = "" )
result_f.grid( row = r, column = 2, **fmt )

r += 1
ttk.Label( root, text = 'Act on StringVar Change' ).grid( row = r, column = 0, **fmt )
ent_trace = ttk.Entry( root, textvariable = trace_v )
ent_trace.grid( row = r, column = 1, **fmt )
result_t = ttk.Label( root, text = "" )
result_t.grid( row = r, column = 2, **fmt )

r += 1
l = ttk.Label( root, text = 'Act on no key entered for 1 second' )
l.grid( row = r, column = 0, **fmt )
ent_wait = ttk.Entry( root, textvariable = wait_v )
ent_wait.grid( row = r, column = 1, **fmt )
result_w = ttk.Label( root, text = "" )
result_w.grid( row = r, column = 2, **fmt )

def on_focus_out( event ):
    """ Change the result label once the Entry loses the focus """
    result_f.config( text = focus_v.get() )

def on_trace( a, b, c ):
    """ Change the result label as the StringVar changes. """
    result_t.config( text = trace_v.get() )

def on_after():
    result_w.config( text = wait_v.get() )

def noop(): 
    return None 

after_v = root.after(1, noop )

def on_wait( event ):
    """ Change the result label if no new key is pressed for a second. """
    global after_v
    root.after_cancel( after_v )           # Clear the old after call
    after_v = root.after( 1000, on_after ) # Create a new one called in 1000 ms

ent_focus.bind( '<FocusOut>', on_focus_out ) # bind event and callback to entry.

trace_v.trace( 'w', on_trace ) # set the trace function to the StringVar

ent_wait.bind( '<Key>', on_wait ) # Bind the <Key> event to the entry

root.mainloop()