CODEWITHSUNDEEP
javascriptangularjs
Tuan
Tuan

Reputation: 61

AngularJS - binding array value to input ngModel

I have $scope.myArray, and it's binding with an input field by ngModel and the expression {{myArray}}

My issue is when I modified myArray by call changeMyArray(), the input's value did not change. But the expression {{myArray}} is display new value.

So, Why the expression work but input field does not?

I have a way to do, but I want to find a better approach

var newArr = $scope.myArray;
newArr.push("b");
$scope.myArray = angular.copy(newArr);;

Example fiddle

Upvotes: 1

Views: 5545

Answers (3)

Tuan
Tuan

Reputation: 61

I have an explanation for my question. Please correct me if I wrong, very thank.

My Question: Why "myArray" input field does not update when $scope.myArray is changed (Model doesn't update View)?

<input ng-model="myArray" id="myArray">

The answer is AngularJs ng-model doesn't know $scope.myArray is changed. Because ng-model does not perform a deep watch of object (rather than a string or number), it only looks for a change of identity or compares the reference of the objects.

In my case, $scope.myArray is collection. So, although $scope.myArray has changed by push new item (structure is changed), it's reference does not change.

As the result, $setViewValue() and $render() never invoked to update the view.

$render $setViewValue

Solution:

Sol1: Add new item to $scope.myArray, make a copy of myArray object and then asign a copy to $scope.myArray again. By this way, the object reference is changed. AngularJs see that change and update the view.

var newArr = $scope.myArray;
newArr.push("b");
$scope.myArray = angular.copy(newArr);

Sol2: Create custome $watch('email', function(){...}, true). The last parameter is TRUE to let Angular perform a deep watch. Then, in watch's listener function, I manually set $viewValue = newValue and invoke $render() of ngModelController to update the view. In case we have Formatters, we should invokes them in this step.

    $scope.$watch('myArray', function(newValue, oldValue) {
if (newValue !== oldValue) {
        var ctrl = angular.element(document.querySelector('#myArray')).controller('ngModel');

        // Invoke formatter
        var formatters = ctrl.$formatters,
          idx = formatters.length;

        while(idx--) {
            newValue = formatters[idx](newValue);
        }

        ctrl.$render();
  }
    }, true);

Please see my script

Upvotes: 0

Austin Mullins
Austin Mullins

Reputation: 7427

Basically, I think what you want to do is bind the input to a "new entry" scope variable, and then push the value of that variable to your array when the user clicks "Push To". Here's what I mean:

In controller:

$scope.changeMyArray = function() {
    $scope.myArray.push($scope.newEntry);
    $scope.newEntry = "";
}

In HTML:

<input ng-model="newEntry">

But actually:

Really what you want is a way to edit the contents of an array via text, and have updates to that array from elsewhere also update the text. This is actually pretty simple since browsers come with a JSON library.

I implemented it by starting with a known pair of objects:

$scope.myArray = [];
$scope.myArrayString = "[]";

That way you can update the string via ngModel:

<input ng-model="myArrayString">

Watch for changes on this model to update the actual array:

$scope.$watch("myArrayString", function() {
    $scope.myArray = JSON.parse($scope.myArrayString);
});

Then update the string in the changeMyArray function:

$scope.changeMyArray = function() {
    $scope.myArray.push("b"); // Or whatever you would like to add here
    $scope.myArrayString = JSON.stringify($scope.myArray);
}

Experiment in my fork of the Fiddle.

What's going on?

The variable $scope.myArray is an object, and any object in Javascript can be converted to a string (most complex objects end up as the unhelpful "[object Object]"). Arrays will actually display their contents when converted to a string, so binding an array to HTML via {{myArray}} is pretty straightforward.

However, the reverse conversion is not as simple. In general, a text input can't be bound to an array in a two-way fashion as we'd like. The solution, then, is to use an intermediary variable to hold the string value, and use $scope.$watch to keep the two values in sync.

Upvotes: 4

sirrocco
sirrocco

Reputation: 8055

So you seem to be wondering why when pushing to the array, your $watch function doesn't do the increment. That's because the #watch function only checks object reference equality.

When pushing to the array, the reference stays the same. When you copy the array and set it again in the same variable, the reference changes.

That's why @watchCollection works as expected and increments when each item is pushed.

Upvotes: 1

Related Questions