Flutter TextInputFormatter not allowing RegEx

Question

I want my TextFormField to accept a string like ABCDE1234F. I tested the regex online and it works. For some reason, the FextFormField doesn't allow any kind of input when I use the following code.

TextFormField(
    inputFormatters: [
        LengthLimitingTextInputFormatter(10),
        FilteringTextInputFormatter.allow(RegExp(r'[A-Z]{5}[0-9]{4}[A-Z]{1}')),
    ],
    validator: (value) {
        if (value.isEmpty) {
        return 'Please enter some text';
        }
        return null;
    },
    decoration: InputDecoration(
        border: InputBorder.none,
        labelText: 'PAN Number',
    ),
)

A valid string should have 5 uppercase letters, followed by 4 digits and a last uppercase letter.

Edit: Playing around more with it, I realized that the issue is in {}. When I just allow digits or numbers without limiting the number with {}, it works. But I can't limit seem to limit number of characters.

question from:https://stackoverflow.com/questions/66058512/flutter-textinputformatter-not-allowing-regex

Answer 1

Your regex pattern should be

RegExp(r'([A-Z]{5}[0-9]{4}[A-Z]{1}$)|([A-Z]{5}[0-9]{1,4}$)|[A-Z]{1,5}$')

and

validator: (value) {
RegExp regExp = new RegExp(r'[A-Z]{5}[0-9]{4}[A-Z]{1}$');
if (value.isEmpty) {
     return 'Please enter some text';
}else if (regExp.hasMatch(value)){
     return "input more."
}
     return null;
},