title: Return error message if password or user email wrong in flutter login form
body: <p>Hy Guys I have connected flutter to my firebase project and used AUTH feature in Firebase but what I would do is to show an error message when a wrong password or Email user is wrong.
  this is my code:</p>
  <pre><code>Widget submitButton (){
      return Container(
        child: SizedBox(
          width: 220,
          height: 40,
          child: MaterialButton(
            elevation: 5,
            onPressed: () async {
              setState(() {
                showProgress = true;
              });
  
              try {
                final newUser = await _auth.signInWithEmailAndPassword(email: email, password: password);
                print(newUser.toString());
                if (newUser != null) {
                  Navigator.push(context, PageTransition(
                    type: PageTransitionType.fade,
                    child: WelcomeScreen(),
                  ));
                  setState(() {
                    showProgress = false;
                  });
  
                }
              } catch (e) {}
            },
            child: Text('Accedi',style: TextStyle(color: Colors.black),),
            color: Colors.white,
            shape: RoundedRectangleBorder(
                borderRadius: BorderRadius.circular(8),
                side: BorderSide(color: Colors.black12,width: 1)),
          ),
  
        ),
      );
    }
  </code></pre>