Question

我正在构建一个GUI，当我按下搜索条目按钮时，在frontend.py的第12行出现了NoneType错误。我不明白该错误完全说明了什么。有人可以解释对此问题的解决方案吗？ frontend.py中的search_command函数连接到backend.py中的搜索函数。也许我缺少明显的东西。

这是我的代码frontend.py

from tkinter import *
import backend


def view_command():
    list1.delete(0,END)
    for row in backend.view():
        list1.insert(END,row)

def search_command():
    list1.delete(0,END)
    for row in backend.search(title_text.get(),author_text.get(),year_text.get(),isbn_text.get()):
        list1.insert(END,row)


window = Tk()

# Label widgets
l1=Label(window, text="Title")
l1.grid(row=0,column=0)

l2=Label(window, text="Author")
l2.grid(row=0,column=2)

l3=Label(window, text="Year")
l3.grid(row=1,column=0)

l4=Label(window, text="ISBN")
l4.grid(row=1,column=2)

# Entry widgets

title_text=StringVar()
e1=Entry(window,textvariable=title_text)
e1.grid(row=0,column=1)

author_text=StringVar()
e2=Entry(window,textvariable=author_text)
e2.grid(row=0,column=3)

year_text=StringVar()
e3=Entry(window,textvariable=year_text)
e3.grid(row=1,column=1)

isbn_text=StringVar()
e4=Entry(window,textvariable=isbn_text)
e4.grid(row=1,column=3)

# List box

list1=Listbox(window, height=6,width=35)
list1.grid(row=2,column=0,rowspan=6,columnspan=2)

# Scroll bar
sb1=Scrollbar(window)
sb1.grid(row=2,column=2,rowspan=6)

list1.configure(yscrollcommand=sb1.set)
sb1.configure(command=list1.yview)

# Buttons

b1=Button(window,text="View All", width=12,command=view_command)
b1.grid(row=2,column=3)

b2=Button(window,text="Search entry", width=12,command=search_command)
b2.grid(row=3,column=3)

b3=Button(window,text="Add Entry", width=12)
b3.grid(row=4,column=3)

b4=Button(window,text="Update", width=12)
b4.grid(row=5,column=3)

b5=Button(window,text="Delete", width=12)
b5.grid(row=6,column=3)

b6=Button(window,text="Close", width=12)
b6.grid(row=7,column=3)


window.mainloop()

这是后端脚本

import sqlite3

def connect():
    conn=sqlite3.connect("books.db")
    cur=conn.cursor()
    cur.execute("CREATE TABLE IF NOT EXISTS book (id INTEGER PRIMARY KEY, title text, author text, year integer, isbn integer)")
    conn.commit()
    conn.close()

def insert(title,author,year,isbn):
    conn=sqlite3.connect("books.db")
    cur=conn.cursor()
    cur.execute("INSERT INTO book VALUES (NULL,?,?,?,?)",(title,author,year,isbn))
    conn.commit()
    conn.close()


def view():
    conn=sqlite3.connect("books.db")
    cur=conn.cursor()
    cur.execute("SELECT * FROM book")
    rows=cur.fetchall()
    conn.close()
    return rows

def search(title="",author="",year="",isbn=""):
        conn=sqlite3.connect("books.db")
        cur=conn.cursor()
        cur.execute("SELECT * FROM book WHERE title=? OR author=? OR year=? OR isbn=?", (title,author,year,isbn))
        rows=cur.fetchall()
        conn.close()

def delete(id):
    conn=sqlite3.connect("books.db")
    cur=conn.cursor()
    cur.execute("DELETE FROM book WHERE id=?",(id,))
    conn.commit()
    conn.close()

def update(id,title,author,year,isbn):
    conn=sqlite3.connect("books.db")
    cur=conn.cursor()
    cur.execute("UPDATE book SET title=?, author=?, year=?, isbn=? WHERE id=?",(title,author,year,isbn,id))
    conn.commit()
    conn.close()


connect()
#insert("The sun","jds", 1918,90919191)
#delete(3)
#update(4,"The moon","John Smooth",1917,28282828)
#print(view())
print(search(author="John Smooth"))

Answer 1

backend.search不返回任何内容（即返回None）。然后，您尝试遍历前端行12中的返回值（None）。您是要

return rows

来自backend.search？

当我按GUI上的“搜索”按钮时，我得到TypeError：'NoneType'对象不可迭代。

1 个答案: