flutter - 传递给另一个小部件时，Flutter formKey currentstate为null

Question

我正在尝试创建一个具有如下disabled属性的 Textbutton 小部件：

class AppTextButton extends StatelessWidget {
  final String title;
  final void Function(BuildContext context) onPress;
  final EdgeInsetsGeometry margin;
  final EdgeInsetsGeometry padding;
  final double borderRadius;
  final Color backgroundColor;
  final Image? leadingIcon;
  final Image? trailingIcon;
  final TextStyle? textStyle;
  final bool disabled;

  AppTextButton(this.title, this.onPress,
      {this.margin = const EdgeInsets.all(0),
      this.padding = const EdgeInsets.all(12),
      this.borderRadius = 0,
      this.leadingIcon,
      this.trailingIcon,
      this.textStyle,
      this.disabled = false,
      this.backgroundColor = const Color(0xFFFFFFFF)});

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: margin,
      child: TextButton(
        style: ButtonStyle(
            shape: MaterialStateProperty.all<RoundedRectangleBorder>(
                RoundedRectangleBorder(
                    borderRadius: BorderRadius.circular(borderRadius))),
            backgroundColor: MaterialStateProperty.all(backgroundColor)),
        child: Row(
          children: [
            if (this.leadingIcon != null) ...[this.leadingIcon!],
            Expanded(
              child: Padding(
                padding: padding,
                child:
                    Text(title, textAlign: TextAlign.center, style: textStyle),
              ),
            ),
            if (this.trailingIcon != null) ...[this.trailingIcon!]
          ],
        ),
        onPressed: () => !disabled ? onPress(context) : null,
      ),
    );
  }
}

在我的屏幕上，我声明我的 formKey 和我的表单如下：

class LoginScreen extends AppBaseScreen {
  LoginScreen({Key? key}) : super(key: key);

  final _formKey = GlobalKey<FormState>();

@override
  Widget build(BuildContext context) {
              Form(
                  key: _formKey,
                  child: Obx(
                    () => AppTextInput(
                      "Please input passcode",
                      _passwordController,
                      borderRadius: 8,
                      fillColor: Color(0xFFF6F4F5),
                      keyboardType: TextInputType.number,
                      errorMessage: _c.errorLoginConfirm.value,
                      isObscure: true,
                      onChange: _onInputChange,
                      maxLength: 6,
                      margin: EdgeInsets.only(top: 12, left: 20, right: 20),
                      validator: (text) {
                        if (text != null && text.length > 0) {
                          if (text.length < 6) {
                            return "Passcode must have at least 6 digits";
                          }
                        }
                      },
                    ),
                  )),

我将在屏幕底部有一个按钮，我!_formKey.currentState!.validate()在禁用字段中传递

AppTextButton("Login", _onLogin,
                  margin: EdgeInsets.fromLTRB(24, 24, 24, 8),
                  backgroundColor: Color(0xFFFF353C),
                  disabled: !_formKey.currentState!.validate(),
                  textStyle: TextStyle(color: Colors.white),
                  borderRadius: 8),

但是，formKey.currentState 为 null 并在每次打开屏幕时抛出以下错误。 Null check operator used on a null value

我在这里做错了什么？先感谢您！

标签： flutterdart-null-safetyflutter-form-builder

Answer 1

传递前需要保存表单状态，

final FormState formState = _formKey.currentState;
formState.save();


onPressed: () {
                FocusScope.of(context).requestFocus(FocusNode());
                final FormState formState = _formKey.currentState;
                if (formState.validate()) {
                  formState.save();
                  onPress(context);
                }
              },