CODEWITHSUNDEEP
flutter
Naik Rahul
Naik Rahul

Reputation: 83

The property 'isEmpty" can't be unconditionally accessed because the receiver can be 'null'

I'm trying to add a validator to a widget:

import 'package:flutter/material.dart';
    import 'package:flutter_app_1/utils/routes.dart';
    
    class LoginPage extends StatefulWidget {
      @override
      _LoginPageState createState() => _LoginPageState();
    }
    
    class _LoginPageState extends State<LoginPage> {
      String name = "";
      bool changeButton = false;
    
      final _formKey = GlobalKey<FormState>();
    
      moveToHome(BuildContext context) async {
        if (_formKey.currentState.validate()) {
          setState(() {
            changeButton = true;
          });
          await Future.delayed(Duration(seconds: 1));
          await Navigator.pushNamed(context, MyRoutes.homeRoute);
          setState(() {
            changeButton = false;
          });
        }
      }
    
      @override
      Widget build(BuildContext context) {
        return Material(
            color: Colors.white,
            child: SingleChildScrollView(
              child: Form(
                key: _formKey,
                child: Column(
                  children: [
                    Image.asset(
                      "assets/images/login_image.png",
                      fit: BoxFit.cover,
                      height: 500,
                    ),
                    SizedBox(
                      height: 20.0,
                    ),
                    Text(
                      "Welcome $name",
                      style: TextStyle(fontSize: 22, fontWeight: FontWeight.bold),
                    ),
                    SizedBox(
                      height: 28.0,
                    ),
                    Padding(
                      padding: const EdgeInsets.symmetric(
                          vertical: 16.0, horizontal: 32.0),
                      child: Column(
                        children: [
                          TextFormField(
                            decoration: InputDecoration(
                              hintText: "Enter User Name",
                              labelText: "Username",
                            ),
                            validator: (String? value) {
                              if (value != null && value.isEmpty) {
                                return "Username can't be empty";
                              }
    
                              return null;
                            },
                            onChanged: (value) {
                              name = value;
                              setState(() {});
                            },
                          ),
                          TextFormField(
                            obscureText: true,
                            decoration: InputDecoration(
                              hintText: "Enter password",
                              labelText: "Password",
                            ),
                            validator: (String? value) {
                              if (value != null && value.isEmpty) {
                                return "Password can't be empty";
                              }
    
                              return null;
                            },
                          ),
                          SizedBox(
                            height: 40.0,
                          ),
                          Material(
                            color: Colors.deepPurple,
                            borderRadius:
                                BorderRadius.circular(changeButton ? 50 : 8),
                            child: InkWell(
                              onTap: () => moveToHome(context),
                              child: AnimatedContainer(
                                duration: Duration(seconds: 1),
                                width: changeButton ? 50 : 150,
                                height: 50,
                                //color: Colors.deepPurple,
                                alignment: Alignment.center,
                                child: changeButton
                                    ? Icon(
                                        Icons.done,
                                        color: Colors.white,
                                      )
                                    : Text(
                                        "Login",
                                        style: TextStyle(
                                            color: Colors.white,
                                            fontWeight: FontWeight.bold,
                                            fontSize: 18),
                                      ),
                                // decoration: BoxDecoration(
                                //     //color: Colors.deepPurple,
                                //     // shape: changeButton
                                //     //     ? BoxShape.circle
                                //     //     : BoxShape.rectangle,
                                //     ),
                              ),
                            ),
                          ),
                          // ElevatedButton(
                          //     child: Text("Login"),
                          //     style: TextButton.styleFrom(minimumSize: Size(150, 40)),
                          //     onPressed: () {
                          //       Navigator.pushNamed(context, MyRoutes.homeRoute);
                          //     })
                        ],
                      ),
                    )
                  ],
                ),
              ),
            ));
      }
    }

but I'm getting this error:

The method 'validate' can't be unconditionally invoked because the receiver can be 'null'. Try making the call conditional (using '?.') or adding a null check to the target ('!')

Upvotes: 8

Views: 28722

Answers (3)

Jai Sawle
Jai Sawle

Reputation: 1

the correct if statement:

moveToHome(BuildContext context) async {
    if (_formkey.currentState!.validate()) {
      setState(() {
        changeButton = true;
      });
      await Future.delayed(Duration(seconds: 1));
      await Navigator.pushNamed(context, MyRoutes.HomeRoute);
      setState(() {
        changeButton = false;
      });

form null safety issues:

TextFormField(
                    // ignore: prefer_const_constructors
                    decoration: InputDecoration(
                        hintText: "Enter Username", labelText: "Username"),

                    validator: (value) {
                      if (value?.isEmpty ?? true) {
                        return "Username cannot be empty";
                      }

                      return null;
                    },
                    onChanged: (value) {
                      name = value;
                      setState(() {});
                    },
                  ),

                  // ignore: prefer_const_constructors
                  SizedBox(
                    height: 20.0,
                  ),
                  TextFormField(
                    obscureText: true,
                    // ignore: prefer_const_constructors
                    decoration: InputDecoration(
                        hintText: "Enter Password", labelText: "Password"),

                    validator: (value) {
                      if (value?.isEmpty ?? true) {
                        return "Password cannot be empty";
                      } else if (value!.length < 6) {
                        return "Password length should be atleast 6";
                      }

                      return null;
                    },
                  ),

Upvotes: 0

BLKKKBVSIK
BLKKKBVSIK

Reputation: 3548

The error you're facing came from null-safety, the value that you're getting from the validator method can be either null or either a String, so you may want to update your code to this example:

validator: (String? value) {                        
  if (value!.isEmpty) {
    return "Username cann't be empty";
  }

  return null;
}

You can learn more about null safety on official documentation:

https://dart.dev/null-safety

Upvotes: 9

Rohan Thacker
Rohan Thacker

Reputation: 6337

You need to make the code null safe, to do that you have a few options, depending on what values you expect.

If you want a String value only then set the initialValue to '' and update the validator condition to (value!.isEmpty) add an ! after value.

If the value really can be null, then add a test to ensure that members are only accessed when the value isn’t null, that is if initialValue is set to null, then you would need to update validator to check for null.

validator: (String? value) {                        
  if (value != null && value.isEmpty) {
    return "Username can't be empty";
  }

  return null;
}

If you want to know more about null-safety in dart check the official docs

Upvotes: 15

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