how to turn disabled button into enabled button depending on conditions

Question

I'm new to flutter and I'm trying to make a button disabled as long as some text fields are empty, so i made 3 textcontrollers to act as a controller for the 3 text fields and i made a function to check the function is:

bool isEmpty(){
    setState(() {
          if(textEditingController.text!=" "&&textEditingController2.text!=" "&& textEditingController3.text!=" "){
            isButtonEnabled=true;


          }
        });
       return isButtonEnabled; 
  }

And the code for the text field is:

TextField(
                  onSubmitted:null,

                  controller: textEditingController3,


                )

Then i write the code for the button as follows: Center(

  child: RaisedButton(
         child: Text("Button 1",style: TextStyle(color:Colors.white),),
          onPressed:isButtonEnabled?(){ print("enabled");}:null,
          color: Colors.red,

            ),

The problem is the button remains disabled even after i write in the text fields. Any idea? Thanks in advance. EDIT: thanks to @diegoveloper answer this worked, but what if i wanted to put intital value and i want the button to be enabled only if the text fields have values for the text fields as following :

@override
  void initState() {
    super.initState();
   textEditingController  = new TextEditingController(text: name);
      textEditingController2  = new TextEditingController(text: email);
         textEditingController3  = new TextEditingController(text: " place");


  }

Then i updated the isEmpty method to be:

bool isEmpty(){
    setState(() {
          if((textEditingController.text!=" ")&&(textEditingController2.text!=" ")&& (textEditingController3.text!=" ")&&(textEditingController!=null)&&(textEditingController2!=null)&&(textEditingController3!=null)){
            isButtonEnabled=true;



          }
          else{
                        isButtonEnabled=false;

          }
        });
       return isButtonEnabled; 
  }

The problem is despite of the intials values i gave to text fields the button is still disabled, also when i edit the 3 values of textfields the button is enabled, but if i deleted the text (in which i think it's meant by null) the button is still disabled.

Answer 1

You could read more about TextField here: https://flutter.io/cookbook/forms/text-field-changes/

So you have two options :

1 - Listen for changes on each TextEditingController and call to your method isEmpty()

2 - Add the onChanged callback on each TextField you want to listen the changes.

Option 2

TextField(
  onSubmitted: null,
  onChanged: (val) {
    isEmpty();
  },
  controller: textEditingController3,
)

Note: don't forget to add the ELSE condition to your isEmpty method.

Edit

Modify your initState method to check if your button is enable (refactor this code please)

@override
void initState() {
    super.initState();

    textEditingController = TextEditingController(text: "name");
    textEditingController2 = TextEditingController(text: "email");
    textEditingController3 = TextEditingController(text: "place");

    if ((textEditingController.text.trim() != "") && (textEditingController2.text.trim() != "") && (textEditingController3.text.trim() != "")) {
        isButtonEnabled = true;
    } else {
        isButtonEnabled = false;
    }
}

Answer 2

You don't need any additional libraries to do that. Flutter has it out-of-the-box and you can make sure you're not going to rebuild the whole tree on each keystroke.

TextEditingController extends ValueNotifier<TextEditingValue> which means you can utilize ValueListenableBuilder from material package to listen to text changes.

class MyWidget extends StatelessWidget {
  final TextEditingController _inputController = TextEditingController();

  @override
  void dispose() {
    _inputController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Column(children: [
      TextField(controller: _inputController),
      ValueListenableBuilder<TextEditingValue>(
        valueListenable: _inputController,
        builder: (context, value, child) {
          return ElevatedButton(
            onPressed: value.text.isNotEmpty ? () {} : null,
            child: Text('I am disabled when text is empty'),
          );
        },
      ),
    ]);
  }
}

Answer 3

You can use nested TextEditingWatchers