validate text in an input field with angular.js

Question

I have an array of strings, lets call them barcodes. I'm using to Angular.js to loop through this array and display the strings and a input field. I need to use angular to validate that when a user enters a new barcode into this input field that it's identical to the string that's displayed right next to it, see example below. I attempting a ng-change event right now which would work if it was just one input field, but because I'm using ng-repeat I cannot make that work. I'm guessing I need to build a directive? I'm new with angular so any help or suggestions would be great. Thanks!

EDIT:

For my purpose I need to alert the user if they enter an incorrect input. My case is unique as the user will not be typing in the input field.. they will be using a barcode scanner, so essentially it is the same as a copy/paste. @KKKKKKKK answer below gets me very close. I made some subtile changes (below) but now this introduces other bugs. with this code below I get the proper alert message but it fires three times? I cannot figure out why..

HTML:

<input type="text" class="form-control matching" ng-model-options="{ updateOn: 'blur' }" ng-model="item.barcodeInput" placeholder="Barcode">
<div ng-show="!isEqualToBarCode($index, item.barcodeInput)"> Error: Value not the same! </div>

In Angular Controller:

$scope.isEqualToBarCode = function(index, val) {
    if(val === null || val === undefined) return true;
    if($scope.barcodes.A_adaptors[index] !== val.trim()) {
        console.log("wrong");
        alert("Incorrect Barcode, Try Again.");
        val = "";
    }
    return $scope.barcodes.A_adaptors[index] === val.trim();
}

Answer 1

Just pass in the $index to your command and then compare it to your array. (Sorry for blind coding errors)

Controller:

$scope.isEqualToBarCode = function(index, val) {

    //if val is empty, don't display error
    if(val === null || val === undefined) return true;

    return $scope.barcodeArray[index].barcodeVal === val.trim();
}

HTML:

<div ng-repeat="item in barcodeArray">
    {{item.barcodeVal}}

    <input ng-model="item.barcodeInput" ng-model-options="{ updateOn: 'blur' }" />

    <div ng-show="!isEqualToBarCode($index, item.barcodeInput)">
        Oh no!  Value not the same!
    </div>

</div>

If you want to set the form validity based on inputted values, then, yes, you would need to write a custom directive.