Example when a specific $scope.apply() is needed:

I am currently delving into the world of Angular and experimenting with different ways to learn how it functions. One of my projects involves creating a simple application where users can add new entries through an HTML interface, store them in a SQLite database, and subsequently edit or delete them.

In order to understand the manual implementation of $scope.apply(), I set up a scenario where its usage was necessary:

Within a function, I stored some variables in localStorage and then manually opened an HTML file:

 localStorage.setItem('idUsuario', response.records[0].idUsuario);
    localStorage.setItem('dato_Nombre', response.records[0].nombre);
    localStorage.setItem('dato_ApPat', response.records[0].apPat);
    localStorage.setItem('dato_ApMat', response.records[0].apMat);
    localStorage.setItem('dato_Direccion', response.records[0].direccion);
    localStorage.setItem('dato_Tel', response.records[0].telefono);
    localStorage.setItem('dato_email', response.records[0].correo);
    //debugger;
    location.href = "editClient.html";

Within the opened HTML file, I utilized ng-init() within my controller to retrieve the stored data and assign it to ng-model variables which were linked to text inputs:

 $scope.init = function () {
    $scope.idUsuario = localStorage.getItem("idUsuario");
    $scope.dato_Nombre = localStorage.getItem("dato_Nombre");
    $scope.dato_ApPat = localStorage.getItem("dato_ApPat");
    $scope.dato_ApMat = localStorage.getItem("dato_ApMat");
    $scope.dato_Tel = localStorage.getItem("dato_Tel");
    $scope.dato_Direccion = localStorage.getItem("dato_Direccion");
    $scope.dato_email = localStorage.getItem("dato_email");

    localStorage.clear();
}

<div class="list">
            <label class="item item-input item-stacked-label">
                <span class="input-label" >Nombre</span>
                <input type="text" placeholder="Escriba su nombre" ng-model="dato_Nombre" >
            </label>
            <label class="item item-input item-stacked-label">
                  <span class="input-label">Apellido Paterno</span>
                <input type="text" placeholder="Escriba su apellido paterno" ng-model="dato_ApPat">
            </label>
            <label class="item item-input item-stacked-label">
                  <span class="input-label">Apellido Materno</span>
                <input type="text" placeholder="Escriba su apellido materno" ng-model="dato_ApMat">
            </label>
            <label class="item item-input item-stacked-label">
                  <span class="input-label">Dirección</span>
                <input type="text" placeholder="Escriba su dirección" ng-model="dato_Direccion">
            </label>
          <label class="item item-input item-stacked-label">
            <span class="input-label">Teléfono</span>
            <input type="text" placeholder="Escriba su teléfono" ng-model="dato_Tel">
          </label>
          <label class="item item-input item-stacked-label">
                  <span class="input-label">Email</span>
              <input type="text" placeholder="Escriba su correo" ng-model="dato_email">
            </label> 
        <center>
          <button class="button button-possitive" ng-click="editarCliente()">Actualizar</button>
        </center>    
        </div>

Upon loading the form, the input fields were successfully populated with data from localStorage. However, upon editing this information and invoking a function to return the updated data within each ng-model variable, I encountered that the changes made in the inputs did not reflect in the ng-model values due to them being still assigned with localStorage data. This led me to consider using $scope.apply().

The issue surfaced when attempting to use $scope.apply(), as an error stating that apply was already running kept appearing, hindering my progress in updating the content of the text inputs.

Answer №1

When $scope.$apply is triggered in an angular application, it initiates a digest cycle. However, if changes are being made within the scope of an existing angular application, there is already a running digest cycle processing the data. This is why encountering an error is common, as having two digest cycles running simultaneously is not recommended. The purpose of $scope.$apply is to handle changes that occur outside of the angular environment, such as integrating non-angular components like jquery plugins or other UI elements that operate independently from Angular's world. In scenarios where updates need to be made within these external elements and reflect on the angular app, using $scope.$apply becomes essential. It may also be necessary when utilizing setTimeout or setInterval instead of the services provided by Angular ($timeout or $interval), as this would execute functions outside of the angular digest cycle.

$.ajax({
 url:'http://lslsls.com',
 method: 'get'
})
.success(function(data){
  var scope = angular.element($('#elementId')).scope();
  scope.returnedData=data;
  scope.$apply();
});

While the jQuery aspect can be disregarded, take note of how the scope is retrieved and updated within the success function. Failing to use scope.$apply() in this situation would result in the values not being reflected in the view until another change triggers a digest cycle.

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