Best way to get values of multiple textfields

You can use something like this in the following code:

_formKey.currentState.save(); calls the onSaved() on each textFormField items, which assigns the value to all the fields and you can use them as required. Try using the _formKey.currentState.save(); just after _formKey.currentState.validate() is evaluated as true.

The form code looks like this:

String contactNumber;
String pin;
return Form(
  key: _formKey,
  child: Column(
    children: <Widget>[
      TextFormField(
        onSaved: (String value){contactNumber=value;},
        keyboardType: TextInputType.phone,
        inputFormatters: [WhitelistingTextInputFormatter.digitsOnly],
        maxLength: 10,
        decoration: InputDecoration(
            labelText: "Enter Your Mobile Number",
            hintText: "Number",
            icon: Icon(Icons.phone_iphone)),
        validator: (value) {
          if (value.isEmpty || value.length < 10) {
            return 'Please Enter 10 digit number';
          }
          return null;
        },
      ),
      TextFormField(
        onSaved: (String value){pin=value;},
        keyboardType: TextInputType.phone,
        inputFormatters: [WhitelistingTextInputFormatter.digitsOnly],
        maxLength: 10,
        decoration: InputDecoration(
            labelText: "Enter Your PIN",
            hintText: "Number",
            icon: Icon(Icons.lock)),
        validator: (value) {
          if (value.isEmpty || value.length < 6) {
            return 'Please Enter 6 digit PIN';
          }
          return null;
        },
      ),
      Padding(
        padding: const EdgeInsets.symmetric(vertical: 16.0),
        child: RaisedButton(
            color: Colors.black,
            textColor: Colors.white,
            onPressed: () {
              if (_formKey.currentState.validate()) {
                ***_formKey.currentState.save();***
                bloc.loginUser(contactNumber, pin);
              }
            },
            child: Text('Login' /*style: TextStyle(fontSize: 30),*/)),
      )
    ],
  ),
);

Using controller in TextFormField, you can get value of the TextFormField.

TextEditingController emailEditingController = TextEditingController();
TextFormField(
  controller: emailEditingController,
  validator: (value) {
    if (value.isEmpty) {
      return 'Please enter a valid email address';
    }
    if (!value.contains('@')) {
      return 'Email is invalid, must contain @';
    }
    if (!value.contains('.')) {
      return 'Email is invalid, must contain .';
    }
    return null;
  },
  keyboardType: TextInputType.emailAddress,
  decoration: InputDecoration(
      prefixIcon: Icon(Icons.mail_outline),
      labelText: 'Enter Email',
      border: OutlineInputBorder()),
);

Get Value like:

String email=emailEditingController.text;

Updated Answer

Get value by using onSubmitted

onSubmitted: (String value){email=value;},