Why i gonna null of the String in Flutter?

Question

I have a problem with a simple thing but I don't how is it happening in the code. Below is the code:

  Widget build(BuildContext context) {
    String newTaskTitle;
    return Container(
      color: Color(0xff757575),
      child: Container(
        padding: EdgeInsets.all(20.0),
        decoration: BoxDecoration(
          color: Colors.white,
          borderRadius: BorderRadius.only(
            topLeft: Radius.circular(20.0),
            topRight: Radius.circular(20.0),
          ),
        ),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            Text(
              'Add Task',
              textAlign: TextAlign.center,
              style: TextStyle(
                fontSize: 30.0,
                color: Colors.lightBlueAccent,
              ),
            ),
            TextField(
              autofocus: true,
              textAlign: TextAlign.center,
              onChanged: (newText) {
                newTaskTitle = newText;
              },
            ),
            FlatButton(
              child: Text(
                'Add',
                style: TextStyle(
                  color: Colors.white,
                ),
              ),
              color: Colors.lightBlueAccent,
              onPressed: () {
                print(newTaskTitle);
              },
            ),
          ],
        ),
      ),
    );
  }

I try to get the value of the text field input and pass it to another screen but when I type something then press the button, it gives me the null.

Answer 1

You can also achieve this using controllers. just initialize one and specify the controller in the TextField widget. To access the text, just do _controlller.text as you can see below:

  final _controller = TextEditingController();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        color: Color(0xff757575),
        child: Container(
          padding: EdgeInsets.all(20.0),
          decoration: BoxDecoration(
            color: Colors.white,
            borderRadius: BorderRadius.only(
              topLeft: Radius.circular(20.0),
              topRight: Radius.circular(20.0),
            ),
          ),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: <Widget>[
              Text(
                'Add Task',
                textAlign: TextAlign.center,
                style: TextStyle(
                  fontSize: 30.0,
                  color: Colors.lightBlueAccent,
                ),
              ),
              TextField(
                controller: _controller,
                autofocus: true,
                textAlign: TextAlign.center,
              ),
              FlatButton(
                child: Text(
                  'Add',
                  style: TextStyle(
                    color: Colors.white,
                  ),
                ),
                color: Colors.lightBlueAccent,
                onPressed: () {
                  print(_controller.text);
                },
              ),
            ],
          ),
        ),
      ),
    );
  }

Answer 2

You have defined String newTaskTitle inside the build() method try removing it from inside the build method and try defining it inside the StatefulWidget.

This is happening because TextField on change method calls build() method every time the text is changed