颤振反应形式无反应形式方法

我正在尝试禁用中的提交按钮 reactive_forms

当我执行此代码时:

import 'package:reactive_forms/reactive_forms.dart';
final form = ReactiveForm.of(context);

我遇到了这个错误:

The following NoSuchMethodError was thrown building VpFormElevatedButton(dirty): The getter 'control' was called on null. Receiver: null Tried calling: control

The relevant error-causing widget was VpFormElevatedButton lib/…/logged_out_nickname/logged_out_nick_name_view.dart:68 When the exception was thrown, this was the stack
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
#1      ReactiveForm.of package:reactive_forms/…/widgets/reactive_form.dart:55
#2      VpFormElevatedButton.build package:vepo/…/buttons/elevated_button_widget.dart:23
#3      StatelessElement.build package:flutter/…/widgets/framework.dart:4701
#4      ComponentElement.performRebuild package:flutter/…/widgets/framework.dart:4627 ... ════════════════════════════════════════════════════════════════════════════════

════════ Exception caught by rendering library ═════════════════════════════════ A RenderFlex overflowed by 99838 pixels on the bottom. The relevant error-causing widget was Column lib/…/logged_out_nickname/logged_out_nick_name_view.dart:65 The specific RenderFlex in question is: RenderFlex#abc1d relayoutBoundary=up1 OVERFLOWING

它认为 ReactiveForm 是一种类型:

final form = ReactiveForm.of(context); 是从reactive_forms文档中复制粘贴的。为什么我看到这个运行时异常?