How to check if Text Field contains a string in flutter?

Question

I have this simple calculator made in Flutter, my problem is I want to check if user inputted a string in a Text Field then (if true) display "Must enter valid number". How can I do this? I'm new to flutter so can someone help me?

I'm aware in using keyboard type as a number but that's not my task. I'm also aware for Text Field validation but that's not what I want, I need to display error message using a Text Widget.

These are my variables and controller

final TextEditingController fController = new TextEditingController();
final TextEditingController sController = new TextEditingController();

String errorMessage = "None";
String result = '0';
double num1, num2;

This is my addNum

void addNum() {
setState(() {
  num1 = double.parse(fController.text);
  num2 = double.parse(sController.text);
  result = (num1 + num2).toString();
});
}

This is the onPressed

onPressed: () {
       addNum();
        if (result.contains('a') || result.contains('a')) {
          setState(() {
            errorMessage = "Invalid";
          });
        }
      },

This is where I display the text

Text(
  "Output: ${result.toString()}\n"
  "Error: ${errorMessage.toString()}",
),

I'm getting an error "Invalid Double a".

Adithaz · Accepted Answer · 2021-03-10 04:02:27Z

4

use https://api.flutter.dev/flutter/widgets/TextEditingController-class.html,

example of usage:

TextEditingController stringController = new TextEditingController();
String errorMessage;

@override
  Widget build(BuildContext context) {
    return Scaffold(
       body: Column(
         children: [
            TextFormField(
               controller: stringController,
            ),
            FlatButton(
               onPressed: () {
                  String a = stringController.text.trim();

                  if(a.isEmpty) {
                     //Put some code here for if string a is empty.
                     setState(() {
                        errorMessage = "Your error message";
                     });
                  }
               }
            ),
            Text(
               errorMessage, 
            ),
         ]
       ),
    ),
}

Try changing text outputs

Text(
   "Output: " + result +
   "\nError: " + errorMessage,
),

edited Mar 10, 2021 at 4:02

answered Mar 10, 2021 at 2:23

Adithaz

4193 silver badges10 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Shoji Yamada Over a year ago

Hello, I provided some codes. Can you please check it out?

Adithaz Over a year ago

Edited @ShojiYamada

deus_magna · Accepted Answer · 2021-03-10 04:24:22Z

This is the right way to do this, you don't need to use a controller, remember to use the most simple and efficient code. Use stateFulWidget. This code generate the error message automatically.

 String isEmpty(String value){
    return value.isEmpty ? 'Required field' : null;
  }


final _formKey = GlobalKey<FormState>();

 return Form(
      key: _formKey,
      child: TextFormField(
      decoration: InputDecoration(
        hintText: 'Your Place holder here',
      ),
      validator: isEmpty,
      onSaved: (String value) {
        _correctTextValue = value;
      },
    ),
);

On your button onPressed() method put this:

_submit() async {
    if (_formKey.currentState.validate()) {
      _formKey.currentState.save();

      // Your code here

    
    }
  }

Gabriel-Ms · Accepted Answer · 2021-07-19 18:31:56Z

0

Try to use controller , like this instead

Before Widget Build:

final _mycontroller = TextEditingController();
 bool _validate = false;

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



On Button:


onPressed(){
setState(){
  _mycontroller2.text.contains("@")
                                 ? _validate = true
                                 : _validate = false;
}}


On TextField:
  TextField(
...
errorText: _validate ? "Insert a valid email": null)

answered Jul 19, 2021 at 18:31

Gabriel-Ms

1

1 Comment

Elydasian Over a year ago

Please provide an explanation of your answer so that the next user knows why this solution worked for you.

Collectives™ on Stack Overflow

How to check if Text Field contains a string in flutter?

3 Answers 3

2 Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related