flutter 传图

FormBuilderCustomField(
                    attribute: "file",
                    validators: [
                      FormBuilderValidators.required(),
                    ],
                    formField: FormField(
                      enabled: true,
                      builder: (FormFieldState<dynamic> field) {
                        return InputDecorator(
                          decoration: InputDecoration(
                            labelText: "Select option",
                            contentPadding:
                                EdgeInsets.only(top: 10.0, bottom: 0.0),
                            border: InputBorder.none,
                          ),
                          child: Column(children: <Widget>[
                            RaisedButton(
                              onPressed: (){
                                _takePhoto(field);
                              },
                              child: Text("拍照"),
                            )
                          ])
                        );
                      },
                    ),
                  ),FormBuilderCustomField(