动态窗体的UnboundField对象错误

Question

我有一个动态表单：

class CollectionRequestParamForm(Form):
    param_human_name = StringField(validators=[DataRequired()])
    param_request_name = StringField()


class CollectionRequestParamCombinedForm(FlaskForm):
    params = FieldList(FormField(CollectionRequestParamForm), min_entries=2)
    submit = SubmitField('Submit')

我想从视图中的代码设置min_entries，比如：

collection_request_params_form = CollectionRequestParamCombinedForm(min_entries=5)

我这样做：

class CollectionRequestParamCombinedForm(FlaskForm):
    def __init__(self, min_entries, *args, **kwargs):
        FlaskForm.__init__(self, *args, **kwargs)
        self.params = FieldList(FormField(CollectionRequestParamForm), min_entries=min_entries)

    submit = SubmitField('Submit')

但是：TypeError: 'UnboundField' object is not iterable

是什么导致了这个错误？你知道吗