Bidirectional data flow in AngularJS Directives

Question

Bidirectional data flow in AngularJS Directives

In an effort to create a dynamic form with different "widgets" based on field types and parameters stored in a database, I have been exploring directives for handling layout changes in response to various scenarios.

After experimenting with some examples, I've managed to come up with code that is somewhat functional:

HTML

<input type="text" ng-model="myModel" style="width: 90%"/>  
<div class="zippy" zippy-title="myModel"></div>

Directive

myApp.directive('zippy', function(){
    return {
      restrict: 'C',
      transclude: true,
      scope: { title:'=zippyTitle' },
      template: '<input type="text" value="{{title}}"style="width: 90%"/>',
      link: function(scope, element, attrs) {
            element.bind('blur keyup change', function() {
                scope.$apply(read);
            });

            var input = element.children();

            function read() {
                scope.title = input.val();
            }
        }
    }
});

While this solution seems to be functioning, albeit with some performance issues compared to standard AngularJS variable binding. I believe there is room for improvement. Can anyone provide insights on how to enhance this approach?

javascript data-binding frameworks angularjs

Answer 1

Answer №1

There's no need to manually trigger the $apply method in this case.

I made some adjustments to the Angular example you referenced and added the input field. I tested it out and it seems to be functioning correctly: http://jsfiddle.net/6HcGS/2/

HTML

<div ng-app="zippyModule">
  <div ng-controller="Ctrl3">
    Title: <input ng-model="title">
    <hr>
    <div class="zippy" zippy-title="title"></div>
  </div>
</div>

JS

function Ctrl3($scope) {
  $scope.title = 'Lorem Ipsum';
}

angular.module('zippyModule', [])
  .directive('zippy', function(){
    return {
      restrict: 'C',
      replace: true,
      transclude: true,
      scope: { title:'=zippyTitle' },
      template: '<input type="text" value="{{title}}" style="width: 90%"/>',
      link: function(scope, element, attrs) {
        // Your controller
      }
    }
  });

UPDATE maxisam pointed out that using ng-model is more appropriate than directly binding the variable to the value:

<input type="text" ng-model="title" style="width: 90%"/>

You can check out the working version here: http://jsfiddle.net/6HcGS/3/

Answer 2

There's no need to manually trigger the $apply method in this case.

I made some adjustments to the Angular example you referenced and added the input field. I tested it out and it seems to be functioning correctly: http://jsfiddle.net/6HcGS/2/

HTML

<div ng-app="zippyModule">
  <div ng-controller="Ctrl3">
    Title: <input ng-model="title">
    <hr>
    <div class="zippy" zippy-title="title"></div>
  </div>
</div>

JS

function Ctrl3($scope) {
  $scope.title = 'Lorem Ipsum';
}

angular.module('zippyModule', [])
  .directive('zippy', function(){
    return {
      restrict: 'C',
      replace: true,
      transclude: true,
      scope: { title:'=zippyTitle' },
      template: '<input type="text" value="{{title}}" style="width: 90%"/>',
      link: function(scope, element, attrs) {
        // Your controller
      }
    }
  });

UPDATE maxisam pointed out that using ng-model is more appropriate than directly binding the variable to the value:

<input type="text" ng-model="title" style="width: 90%"/>

You can check out the working version here: http://jsfiddle.net/6HcGS/3/

Answer 3

Answer №2

Do you mean something along the lines of this example?

I am using a similar approach to @Flek's example.
The only variation is the usage of ng-model='title'

The key to achieving two-way binding is through ng-model, as described in the documentation:

ngModel is a directive that enables Angular to facilitate two-way data binding. It collaborates with input, select, textarea elements. You can also create your own directives to leverage ngModel.

<input type="text" ng-model="title" style="width: 90%"/>

Answer 4

Do you mean something along the lines of this example?

I am using a similar approach to @Flek's example.
The only variation is the usage of ng-model='title'

The key to achieving two-way binding is through ng-model, as described in the documentation:

ngModel is a directive that enables Angular to facilitate two-way data binding. It collaborates with input, select, textarea elements. You can also create your own directives to leverage ngModel.

<input type="text" ng-model="title" style="width: 90%"/>

Answer 5

Answer №3

Here is a method for passing a callback parameter within a directive. This is how the controller template looks:

    <component-paging-select-directive
            page-item-limit="{{pageItemLimit}}"
            page-change-handler="pageChangeHandler(paramPulledOutOffThinAir)"
            ></component-paging-select-directive>

Now, let's take a look at the directive itself:

angular.module('component')
    .directive('componentPagingSelectDirective', [
        function( ) {
            return {
                restrict: 'E',
                scope: { 
                    // using the '=' for two way doesn't work
                    pageItemLimit:  '@', // the '@' is one way from controller
                    pageChangeHandler: '&'
                },
                controller: function($scope) {   
                    // passing value from this scope to controller method. 
                    // The controller method will then update the variable in the controller scope
                    $scope.pageChangeHandler({
                        paramPulledOutOffThinAir: $scope.pageItemLimit
                    })

                }, ...

In the controller:

angular.module('...').controller(...
        $scope.pageItemLimit = 0; // initial value for controller scoped variable

        // completing the data update by setting the variable in the controller scope 
        // equal to the one from the directive
        $scope.pageChangeHandler = function(paramPulledOutOffThinAir) {
            $scope.pageItemLimit = paramPulledOutOffThinAir;
        }

It's important to note the difference in function parameters for the directive (an object with parameter as keys), template ('unwrapped' keys from the parameter object in directive), and controller definition.

Answer 6

Here is a method for passing a callback parameter within a directive. This is how the controller template looks:

    <component-paging-select-directive
            page-item-limit="{{pageItemLimit}}"
            page-change-handler="pageChangeHandler(paramPulledOutOffThinAir)"
            ></component-paging-select-directive>

Now, let's take a look at the directive itself:

angular.module('component')
    .directive('componentPagingSelectDirective', [
        function( ) {
            return {
                restrict: 'E',
                scope: { 
                    // using the '=' for two way doesn't work
                    pageItemLimit:  '@', // the '@' is one way from controller
                    pageChangeHandler: '&'
                },
                controller: function($scope) {   
                    // passing value from this scope to controller method. 
                    // The controller method will then update the variable in the controller scope
                    $scope.pageChangeHandler({
                        paramPulledOutOffThinAir: $scope.pageItemLimit
                    })

                }, ...

In the controller:

angular.module('...').controller(...
        $scope.pageItemLimit = 0; // initial value for controller scoped variable

        // completing the data update by setting the variable in the controller scope 
        // equal to the one from the directive
        $scope.pageChangeHandler = function(paramPulledOutOffThinAir) {
            $scope.pageItemLimit = paramPulledOutOffThinAir;
        }

It's important to note the difference in function parameters for the directive (an object with parameter as keys), template ('unwrapped' keys from the parameter object in directive), and controller definition.

Bidirectional data flow in AngularJS Directives

HTML

Directive

Answer №1

Answer №2

Answer №3

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