javascript - $watchCollection 不适用于数组

Question

我正在使用 $watchCollection 来观察数组长度的变化。但是当我将任何项目添加到数组时它似乎不起作用。我哪里出错了？

var app = angular.module('plunker', []);

app.controller('MainCtrl', function($scope) {

  $scope.count;
  $scope.Items = {
      "Cars" : [
          {
              "id" : 1,
              "name" : "Mercedes"
          },
          {
              "id": 2,
              "name" : "Ferrari"
          }

      ],
      "Bikes" : [
           {
              "id" : 1,
              "name" : "Ducati"
          },
          {
              "id": 2,
              "name" : "Yamaha"
          } 

      ]
  }

  $scope.addCar = function() {
    $scope.Items.Cars.push({
        'id' : 3,
        "name" : "random name"
    })
  }

  $scope.$watchCollection($scope.Items.Cars, function(newNames, oldNames) {
    $scope.count = $scope.Items.Cars.length;
    console.log($scope.count);
  })

});

演示:http://plnkr.co/edit/dSloJazZgr3mMevIHOe8?p=preview

Answer 1

您应该将表达式作为第一个变量传递给 $watchCollection ，不是对象:

$scope.$watchCollection('Items.Cars', function(newNames, oldNames) {
  $scope.count = $scope.Items.Cars.length;
  console.log($scope.count);
})

plnkr example .