flask-wtf validate_on_submit()

验证用户名和密码，validate_on_validate()返回值因为True，但是下面的代码却是False，求解答：

class LoginForm(Form):
    username = StringField('Username')
    password = PasswordField('Password')
    submit = SubmitField('Login')
    def validate_username(self, field):
        if field.data != 'you':
            raise ValidationError('Invalid username')
    def validate_password(self, field):
        if field.data != 'flask':
            raise ValidationError('Invalid password')

@app.route('/', methods=['POST', 'GET'])
def login_view():
    form = LoginForm()
    if form.validate_on_submit():
            flash('Username and password are correct')
            return redirect('/')
    return render_template('form.html', form = form)

如上form.validate_on_submit()返回值总是为False
我只能把代码改为：

@app.route('/', methods=['POST', 'GET'])
def login_view():
    form = LoginForm()
    if request.method == 'POST':
        if not form.validate_on_submit():
            flash('Username and password are correct')
            return redirect('/')
    else:
        return render_template('form.html', form = form)

这样才会有用，求解答

---

问题可能是因为你的表单里StringField和PasswordField没有validators，如果表单里没有写validators的话，相当于你提交的表单内容是空，后端的form.validate_on_submit()就会一直是false。
试试这种写法

username = StringField('Username',validators=[Required()])
password = PasswordField('Password',validators=[Required()])

如果你的username和password需要特殊格式的话，这里validators可能不只要写Required。我的登录验证表单是这样写的

email = StringField('Email',validators=[Required(),Length(1,64),Email()])
password = PasswordField('Password',validators=[Required()])

这里需要引入一些验证的包或者叫验证函数

from wtforms.validators import Required,Email

可以参考一下这里
http://stackoverflow.com/questions/20170234/validate-on-submit-always-returns-false-using-flask-wtforms