General method
All those who have done the front-end work should have submitted the form. Take text input as an example, the general TextField component is provided in flutter

TextField(
      decoration: InputDecoration(labelText: 'Product name'),
      onChanged: (String value) {
        setState(() {
          _name = value;
        });
        print(value);
      },
    );

onChanged callback a method containing the String value parameter, which assigns a value to the property through the setState method

TextFormField

//Form state
  GlobalKey<FormState> _formKey = GlobalKey<FormState>();

@override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Container(
        margin: EdgeInsets.all(10.0),
        child: Form(
        //Binding state properties
            key: _formKey,
            child: ListView(
              children: <Widget>[
                _buildNameText(),
                _buildDescriptionText(),
                _buildPriceText(),
                Container(
                  padding: EdgeInsets.all(10.0),
                  child:
                      RaisedButton(child: Text('Add to'), onPressed: _submitValues),
                )
              ],
            )));
  }

Widget _buildNameText() {
    return TextFormField(
      decoration: InputDecoration(labelText: 'Product name'),
      validator: (String value) {
        //Remove leading and trailing spaces
        if (value.isEmpty || value.trim().length <= 5) {
          return 'The number of name words must be greater than 5';
        }
      },
      onSaved: (String value) {

          text = value;

      },
    );
  }

flutter provides a set of solutions for form submission. It is mainly composed of Form,TextFormField, component, globalkey < formstate > attribute. onSaved callback a method with String value as parameter. The calling time is different from onChanged, and it will be called when ﹐ formKey.currentState.save() is executed. The validator in TextFormField is a verifier, and it also calls back a method, which can be customized The condition returns the error message. Its function will be called in ﹐ formKey.currentState.validate(); method call is a callback