angular1.x---angular中清除定时器$interval，解决重复计算问题

用angular1.x版本做定时器的时候，需要用到内置对象'$interval'，用到window原生的setInterval的时候不能及时更新数据，但是’$interval’定义的定时器却不像setInterval那么容易清除。

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查看源码，angular提供有例子进行说明定时器的清除：

<script>
      *     angular.module('intervalExample', [])
      *       .controller('ExampleController', ['$scope', '$interval',
      *         function($scope, $interval) {
      *           $scope.format = 'M/d/yy h:mm:ss a';
      *           $scope.blood_1 = 100;
      *           $scope.blood_2 = 120;
      *
      *           var stop;
      *           $scope.fight = function() {
      *             // Don't start a new fight if we are already fighting
      *             if ( angular.isDefined(stop) ) return;
      *
      *             stop = $interval(function() {
      *               if ($scope.blood_1 > 0 && $scope.blood_2 > 0) {
      *                 $scope.blood_1 = $scope.blood_1 - 3;
      *                 $scope.blood_2 = $scope.blood_2 - 4;
      *               } else {
      *                 $scope.stopFight();
      *               }
      *             }, 100);
      *           };
      *
      *           $scope.stopFight = function() {
      *             if (angular.isDefined(stop)) {
      *               $interval.cancel(stop);
      *               stop = undefined;
      *             }
      *           };
      *
      *           $scope.resetFight = function() {
      *             $scope.blood_1 = 100;
      *             $scope.blood_2 = 120;
      *           };
      *
      *           $scope.$on('$destroy', function() {
      *             // Make sure that the interval is destroyed too
      *             $scope.stopFight();
      *           });
      *         }])
      *       // Register the 'myCurrentTime' directive factory method.
      *       // We inject $interval and dateFilter service since the factory method is DI.
      *       .directive('myCurrentTime', ['$interval', 'dateFilter',
      *         function($interval, dateFilter) {
      *           // return the directive link function. (compile function not needed)
      *           return function(scope, element, attrs) {
      *             var format,  // date format
      *                 stopTime; // so that we can cancel the time updates
      *
      *             // used to update the UI
      *             function updateTime() {
      *               element.text(dateFilter(new Date(), format));
      *             }
      *
      *             // watch the expression, and update the UI on change.
      *             scope.$watch(attrs.myCurrentTime, function(value) {
      *               format = value;
      *               updateTime();
      *             });
      *
      *             stopTime = $interval(updateTime, 1000);
      *
      *             // listen on DOM destroy (removal) event, and cancel the next UI update
      *             // to prevent updating time after the DOM element was removed.
      *             element.on('$destroy', function() {
      *               $interval.cancel(stopTime);
      *             });
      *           }
      *         }]);
      *   </script>

一大串代码，似乎不太容易，远不止简单的设置timer=null就可以解决的，虽然可以实现，但是今天在公司项目中遇到了问题，无论如何仿照源码都无法解决问题，于是继续寻找并打印$interval源码：

function interval(fn, delay, count, invokeApply) {
var hasParams = arguments.length > 4,
          args = hasParams ? sliceArgs(arguments, 4) : [],
          setInterval = $window.setInterval,
          clearInterval = $window.clearInterval,
          iteration = 0,
          skipApply = (isDefined(invokeApply) && !invokeApply),
          deferred = (skipApply ? $$q : $q).defer(),
          promise = deferred.promise;

      count = isDefined(count) ? count : 0;

      promise.then(null, null, (!hasParams) ? fn : function() {
        fn.apply(null, args);
      });

      promise.$$intervalId = setInterval(function tick() {
        deferred.notify(iteration++);

if (count > 0 && iteration >= count) {
          deferred.resolve(iteration);
          clearInterval(promise.$$intervalId);
          delete intervals[promise.$$intervalId];
        }

if (!skipApply) $rootScope.$apply();

      }, delay);

      intervals[promise.$$intervalId] = deferred;

return promise;
    }

源码中，$interval定义一个定时器可以传入四个参数(fn, delay, count, invokeApply)：

fn://定时器的执行函数
delay://每次函数执行的间隔时间
count://函数fn的执行次数
invokeApply://设置脏值检测

通过count的设置便解决今天项目中，数值无限减小问题，代码如下：

$scope.num=60;
$scope.timer=$interval(function(){
$scope.num--;
},1000,$scope.num);
///在切换控制器的时候，清除定时器，减少内存损耗
$scope.$on(
"$destroy",
function() {
$interval.cancel( $scope.timer);
  }
);