Flutter 如何从用户那里获取正确的家庭地址？

我正在使用flatter构建一个应用程序，并向用户询问他们的地址。目前，我使用普通表单字段来获取城市、邮政编码、州和国家等数据，因此一些用户只需在字段中输入任何内容，这些内容甚至没有意义，比如州名不属于该国家/地区列表，与邮政编码和城市相同

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我想限制用户输入正确的数据。例如，如果有人进入美国，则只能输入美国境内的州。我不知道该怎么做。是否有可用的软件包或api？

使用颤振表单验证。这看起来非常冗长，但这就是弗利特如何做到的

将字段包装成表单（）。对于每个字段，您将有一个onChanged函数、一个onsave函数（可能），然后为每个字段添加一个验证器函数。这是最重要的部分。如果数据没有问题，验证程序应该返回null。如果出现问题，它应该返回一个包含错误描述的字符串

这里有一个太大的代码示例：

// <-- Add this widget. (Don't forget to close it!)
        autovalidate: _autovalidate, // <-- Add this line
        key: _key, // <-- Add this line
        child: Container(
          alignment: Alignment.center,
          child: Column(
            children: <Widget>[
              _buildEmailField,
              _buildPasswordField,
              _buildPasswordConfirmationField,
              _buildAgreeToTermsField,
            ],
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.save),
        onPressed: _doRegister,
      ),
    );
  }

  Widget get _buildEmailField {
    return TextFormField(
      // TODO 4: Change to a TextFormField
      decoration: InputDecoration(labelText: "Email"),
      // TODO 5: Add onSaved and validator methods
      onSaved: (String val) => _loginObject['email'] = val,
      validator: _validateEmail,
      // TODO 9: Add autofocus
      autofocus: true,
      // TODO 10: Add a focusNode
      focusNode: _emailFocusNode,
    );
  }

  Widget get _buildPasswordField {
    return TextFormField(
      // TODO 4: Change to a TextFormField
      decoration: InputDecoration(labelText: "Password"),
      obscureText: true,
      onChanged: (String val) => setState(() => _pass1 = val),
      // TODO 6: Add onSaved and validator methods to the password field
      onSaved: (String val) => _loginObject['password'] = val,
      validator: _validatePassword,
    );
  }

  Widget get _buildPasswordConfirmationField {
    return TextFormField(
      // TODO 4: Change to a TextFormField
      decoration: InputDecoration(labelText: "Password (again)"),
      obscureText: true,
      // TODO 7: Validate the password confirmation here
      validator: _validatePasswordConfirmation,
    );
  }

  Widget get _buildAgreeToTermsField {
    // TODO 8: Wrap the Column with a FormField<bool>
    return FormField<bool>(
      // 1
      initialValue: _agree,
      builder: (FormFieldState<bool> state) {
        // 2
        return Column(
          children: <Widget>[
            Row(
              children: <Widget>[
                Checkbox(
                  // 3
                  value: state.value,
                  onChanged: (bool val) => setState(() {
                    // 4
                    _agree = val;
                    // 5
                    state.didChange(val);
                  }),
                ),
                const Text("I agree to the terms."),
              ],
            ),
            // 6
            state.errorText == null
                ? Text("")
                : Text(state.errorText, style: TextStyle(color: Colors.red)),
          ],
        );
      },
      // 7
      validator: (val) => _validateTerms(_agree),
    );
  }

  // Valid if we get a well-formed and non-empty email address
  String _validateEmail(String email) {
    // 1
    RegExp regex = RegExp(r'\w+@\w+\.\w+');
    // Add the following line to set focus to the email field
    if (email.isEmpty || !regex.hasMatch(email)) _emailFocusNode.requestFocus();
    // 2
    if (email.isEmpty)
      return 'We need an email address';
    else if (!regex.hasMatch(email))
      // 3
      return "That doesn't look like an email address";
    else
      // 4
      return null;
  }

  String _validatePassword(String pass1) {
    RegExp hasUpper = RegExp(r'[A-Z]');
    RegExp hasLower = RegExp(r'[a-z]');
    RegExp hasDigit = RegExp(r'\d');
    RegExp hasPunct = RegExp(r'[_!@#\$&*~-]');
    if (!RegExp(r'.{8,}').hasMatch(pass1))
      return 'Passwords must have at least 8 characters';
    if (!hasUpper.hasMatch(pass1))
      return 'Passwords must have at least one uppercase character';
    if (!hasLower.hasMatch(pass1))
      return 'Passwords must have at least one lowercase character';
    if (!hasDigit.hasMatch(pass1))
      return 'Passwords must have at least one number';
    if (!hasPunct.hasMatch(pass1))
      return 'Passwords need at least one special character like !@#\$&*~-';
    return null;
  }

  String _validatePasswordConfirmation(String pass2) {
    return (pass2 == _pass1) ? null : "The two passwords must match";
    // Note that _pass1 is populated when a password is entered
  }

  String _validateTerms(bool agree) {
    return agree ? null : "You must agree before proceeding";
    // It's invalid if the user hasn't opted in by checking the box
  }

  void _doRegister() {
    // After the first attempt to save, turn on autovalidate to give quicker feedback to the user
    setState(() => _autovalidate = true); // <-- Add this line
    // TODO 3: Add validation and saving here
    if (_key.currentState.validate()) {
      // Commit the field values to their variables
      _key.currentState.save();
      print("""
      The user has registered with an email address of '${_loginObject['email']}' 
      and a password of '${_loginObject['password']}'
      """);
    }
  }
}

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