$watch 'miss' 可以吗? [英] Can $watch 'miss'?

问题描述

我们有以下指令:

app.directive("counterWidget",function(){
  return{
    restrict:"E",
    scope:{
      startnumber: '=',
      resetter: '='
    },
    link:function(scope,elem,attr){
        scope.f =  attr.startnumber;
        scope.add = function(){             
            scope.f++
        }
        scope.remove = function(){
            scope.f--
        }
        scope.reset = function(){
            scope.f = attr.startnumber
            scope.$parent.triggerReset()
        }
        scope.$watch(function(attr) {
          return attr.resetter
        },
        function(newVal) {
          if (newVal === true) {
            scope.f = attr.startnumber;
          }
        })

    },
    template:"<button ng-click='add()'>more</button>"+
             "{{f}}"+
             "<button ng-click='remove()'>less</button>&nbsp"+
             "<button ng-click='reset()'>reset</button><br><br>"
    }

  })

在这个指令中有一个监视函数，它监视重置器属性的变化.该属性由控制器中的此函数触发:

In this directive there is a watch function, which watches the resetter attribute for changes. That attribute is triggered by this function in the controller:

$scope.triggerReset = function () {
    $scope.reset = true;
    console.log('reset')
    $timeout(function() {
      $scope.reset = false; 
    },100)
}

问题来了 - $watch 'miss' 可以吗?如果超时时间太短，或者......我不知道......其他原因导致它因某种原因挂断，它是否无法捕捉切换?

The question came up - can $watch 'miss'? If the timeout is too short, or...I don't know...something else causes it to hangup for some reason, can it fail to catch the toggle?

我有以下演示:Plunker

I have the following demo: Plunker

我将超时设置为 1 毫秒，甚至将其全部删除，但它仍然可以正常重置.但是会出现 $watch 变得不可靠的情况吗?

I set the timeout to 1ms, and even removed it all together and it still resets fine. But can some situation arise where a $watch would become unreliable?

推荐答案

没有.您甚至可以将其设置为 0ms，它仍然会捕获.

No. You can even set it to 0ms, and it will still catch.

$timeout 将始终导致其函数内部的代码在与当前循环不同的 $digest 循环中运行.

$timeout will always cause the code internal to its function to run in a different $digest cycle from the current one.

$evalAsync，另一方面，根据情况可能会导致未命中.

$evalAsync, on the other hand, may cause a miss depending on the circumstances.

有关更多详细信息，请参阅此答案:https://stackoverflow.com/a/16066461/624590

See this answer for more details: https://stackoverflow.com/a/16066461/624590

我错过了一个边缘情况，其中第三个参数被传递给 $timeout 函数.如果您调用 $timeout(fn, 50, false)(注意末尾的 false)，它将跳过 $apply 步骤并让你错过"改变.这是基于 $timeout 源代码:https://github.com/angular/angular.js/blob/master/src/ng/timeout.js#L64

I missed an edge-case to this where a third parameter is passed to the $timeout function. If you call $timeout(fn, 50, false) (notice the false at the end), it will skip the $apply step and allow you to "miss" the change. This is based on the $timeout source code: https://github.com/angular/angular.js/blob/master/src/ng/timeout.js#L64

这篇关于$watch 'miss' 可以吗?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！