为什么entry的返回值是空白？

import tkinter as tk

window = tk.Tk()
window.title("ICP")
window.geometry("800x300")

def hit1():
    window1 = tk.Tk()
    window1.title("Add New Item(s)")
    window1.geometry("500x500")
    tk.Label(window1, text="Record number:").place(x=10, y=10)
    tk.Label(window1, text="Item name:").place(x=10, y=50)
    global var_rnum
    global var_iname
    var_rnum = tk.StringVar()
    entry_rnum = tk.Entry(window1, textvariable=var_rnum)
    entry_rnum.place(x=120,y=10)
    var_iname = tk.StringVar()
    entry_iname = tk.Entry(window1, textvariable=var_iname)
    entry_iname.place(x=120,y=50)
    bu = tk.Button(window1,text="sumit",command=hit_1)
    bu.place(x=120,y=370)

def hit_1():
    rnum = var_rnum.get()
    iname = var_iname.get()
    print(rnum)

b1 = tk.Button(window,text="1.Add New Item(s):",command=hit1)
b1.pack()
window.mainloop()

为什么print(rnum)的值是空白啊？

import tkinter as tk



window1 = tk.Tk()
window1.title("Add New Item(s)")
window1.geometry("500x500")
tk.Label(window1, text="Record number:").place(x=10, y=10)
tk.Label(window1, text="Item name:").place(x=10, y=50)

var_rnum = tk.StringVar()
entry_rnum = tk.Entry(window1, textvariable=var_rnum)
entry_rnum.place(x=120,y=10)
var_iname = tk.StringVar()
entry_iname = tk.Entry(window1, textvariable=var_iname)
entry_iname.place(x=120,y=50)



   
def hit_1():
    rnum = var_rnum.get()
    iname = var_iname.get()
    print(rnum)



bu = tk.Button(window1,text="sumit",command=hit_1)
bu.place(x=120,y=370)
window1.mainloop()

这样写的话 print(rnum)的值是正常显示的