TextField 不会将数据传递给同一类中的另一个 flutter Widget

Question

Here we have stateless AddTaskScreen widget, inside widget tree we have a TextField to get data and pass it over to another widget.Namely to pass it to the onPressed property of FlatButton widget.

Here is problem: when typing something in TextField its callback works fine and print value correctly, but when press FlatButton it pass over a null data instead of value of TextField, actually it did not store value of TextField in newTaskTitle variable to pass it to Flat button.

Thank for your support, can you help me find out the problem?

class AddTaskScreen extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
  String newTaskTitle;//Here i declare newTasktitle to store value of TextField

    return Container(
      color: Color(0xff757575),
      child: Container(
        padding: EdgeInsets.all(20),
        decoration: BoxDecoration(
          color: Colors.white,
          borderRadius: BorderRadius.only(topRight: Radius.circular(30),topLeft: Radius.circular(30))
        ),
        child: Column(
          children: [
            TextField(
              onChanged: (textValue){
                newTaskTitle = textValue;
                print(newTaskTitle);//works fine at this step
              },
            ),
            SizedBox(height: 15),
            FlatButton(
              child: Text('add',style: TextStyle(color: Colors.white),),
              onPressed:(){
                print(newTaskTitle);//result: null
                //here we get null as newTaskTitle value,why?
                Provider.of<TaskData>(context,listen: false).addTask(newTaskTitle);
                Navigator.pop(context);
              },
            ),

          ],
        ),
      ),
    );
  }
}

Answer 1

In this case you should use Stateful widget for save textField value. You need to use setState({}) for update this value.

Answer 2

I suggest you use TextEditingController for more easy use, here's how you use it:

Declare your TextEditingController :

final TextEditingController _txtTask = TextEditingController();

Put it inside your TextField:

                TextField(
                  controller: _txtTask,
                ),

This is how you get the value

_txtTask.text

No need to put any function such onChanged, just use it like this _txtTask.text to get the value. And everything that work with changing state you need to change your class to StatefulWidget . I hope this is helpful, it might not as you wanted but this is the best workaround.