如何用ng-change观看select的变化？

Question

Any idea how can I update the total when the selected value changed? http://jsfiddle.net/yx97x0xk/1

angular.module('app', ['QuickList']).controller('mainCtrl', function($scope) {
  $scope.getSum = function() {
    return $scope.myJson.map(function(x) {
      return x.price * x.qty
    }).reduce(function(a, b) {
      return a + b
    });
  }

  $scope.myJson = [{
    "id": "1",
    "name": "banana",
    "price": 12,
    "qty": 3,
  }, {
    "id": "2",
    "name": "watermelon",
    "price": 12.9,
    "qty": 4,
  }]

})

Answer 1

They are not the same, clearly. One is used solely in the controller; the other is a directive on an input element.

But even in their application they differ.

When you use $watch the watched expression will be evaluated on every digest cycle, and if there is a change, the handler is invoked.

With ng-change, the change is restricted to a user action on a particular input element.

With ng-change, the handler is invoked explicitly in response to an event.

With $watch, change can come from anywhere: user action, controller function, service - all will trigger the handler.

Answer 2

Just use ng-model="json.qty" in your select tag and remove ng-selected from option tag. This will do the trick. :-)

Angular will automatically execute a function ( getSum in this case) if the returning value from the function changes.

See it working below:

 angular.module('app', []).controller('mainCtrl', function($scope) { $scope.getSum = function() { return $scope.myJson.map(function(x) { return x.price * x.qty }).reduce(function(a, b) { return a + b }); }; $scope.myJson = [{ "id": "1", "name": "banana", "price": 12, "qty": 3, }, { "id": "2", "name": "watermelon", "price": 12.9, "qty": 4, }] }); 

 <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script> <div ng-app='app' ng-controller='mainCtrl'> <div ng-repeat="json in myJson"> <li>{{json.name}}</li> <select name="" id="" ng-model="json.qty"> <option ng-repeat="i in [1,2,3,4,5,6,7,8,9,10]">{{$index + 1}}</option> </select> </div> <h1>total:{{getSum()}}</h1> </div>