ng-if 被调用的次数多于它应该调用的次数

问题描述

我正在尝试根据所选类别过滤一些频道.

I'm trying to filter some channels depending on the selected category.

我有一个 channel in channels 的 ng-repeat，它有一个 ng-if="hasCategory(channel.category)

I have an ng-repeat of channel in channels which has an ng-if="hasCategory(channel.category)

文档如下:

db.channels.find().pretty()
{
    "_id" : "2kj9GK8jE9yHezoWb",
    "name" : "example name",
    "logo" : "path/to/image.svg",
    "number" : 2,
    "category" : [
        "Broadcast",
        "Premium"
    ],
    "tags" : "example tag tags"
}

这是处理ng-if的函数:

This is the function to handle the ng-if:

$scope.hasCategory = function (categoryNameArray) {
  console.log('thisisbeingcalled');
  var e = _.indexOf(categoryNameArray, $scope.activeCategory);
  if (e === -1) {
    return false;
  } else {
    return true;
  }
};

这就是我设置活动类别的方式:

and this is how I set the active category:

$scope.setCategory = function (name) {
  $scope.activeCategory = name;
};

我通过单击视图中的按钮发送:

which I send by clicking the button in the view:

<section layout="row" layout-align="center center" layout-wrap ng-init="activeIndex; activeCategory">
  <md-button flex="auto" flex-sm="45" flex-xs="100" ng-repeat="kit in kits | orderBy: 'order'" ng-class="{active: (activeIndex.index == $index)}" class="md-raised">
    <a href="" ng-click="activeIndex.index = $index; setCategory(kit.name);" class="bold">{{kit.name}}</a>
  </md-button>
</section>

这是工具包文档架构:

db.kits.find().pretty()
{ "_id" : "k7JFX6DHu5GYnyer3", "name" : "Broadcast", "order" : 1 }
{ "_id" : "KrKRm4gysw5sfQnnr", "name" : "Premium", "order" : 2 }
{ "_id" : "dieukQ3NRsA44CSns", "name" : "Ultimate", "order" : 3 }

现在我只有一个频道来测试这一点，但每次我点击按钮更改类别时，即使在页面启动时也会多次调用 $scope.hasCategory 函数(第一次加载)

Now I only have one channel to test this out, but each time I click the button to change the category, the $scope.hasCategory function gets called multiple times even at the startup of the page (first time loading)

我还有一个搜索栏来搜索当前类别中的频道，我不确定这是否也会影响到这一点.

I also have a search bar to search for channels in the current category, I'm not sure if that affects this as well.

<input type="text" ng-model="queryname" ng-model-options="{debounce: 500}">

现在当我有超过 100 个频道时这会变得非常滞后，ng-if 被调用超过 10k 次，这使得页面冻结了很长一段时间.

Now this gets really laggy when I have more than a 100 channels, the ng-if gets called more than 10k times, which makes the page freeze for quite a while.

我该怎么做才能解决这个问题?

What can I do to fix this issue?

编辑

忘记添加 ng-if 的位置:

<md-card flex="15" flex-xs="40" class="slide-up" layout="column" ng-repeat="channel in channels | orderBy: 'number' | filter: queryname" ng-if="hasCategory(channel.category)" ng-init="channel.edit = false">
  <md-card-header ng-show="channel.edit == false">
    <img ng-src="{{channel.logo}}" alt="">
  </md-card-header>
  <md-card-header-text ng-show="channel.edit == false">
    <span class="md-subhead dark-blue" layout="row" layout-align="center" layout-margin>{{channel.number}}</span>
  </md-card-header-text>
</md-card>

推荐答案

您的 ng-if 将在每个摘要循环中调用.问题在于它包含一个涉及函数调用的表达式.Angular 无法知道表达式的结果何时可能发生变化，因此每次都会调用它.

Your ng-if will be called on every digest loop. The problem is that it contains an expression involving a function call. Angular has no way to know when the result of the expression might change, so it calls it every time.

更好的选择是在每个通道中设置一个标志并使用 ng-if 来测试相关标志.然后，您只需在 $scope.activeCategory 更改时更新标志，您可以使用设置类别的代码或使用 $scope.$watch()自动触发.

A better option would be to set a flag in each of the channels and use ng-if to just test the relevant flag. Then you just have to update the flags whenever $scope.activeCategory changes which you can either do with code where you set the category or using $scope.$watch() to trigger it automatically.

例如

$scope.setCategory = function (name) {
  $scope.activeCategory = name;
  for (var index=0; index < $scope.channels.length; index++) {
      $scope.channels[index].hasCategory = hasCategory($scope.channels[index].category, name);
  }
};

function hasCategory(categoryNameArray, name) {
  console.log('thisisbeingcalled');
  var e = _.indexOf(categoryNameArray, name);
  if (e === -1) {
    return false;
  } else {
    return true;
  }
}

然后在您的模板中:

<md-card flex="15" flex-xs="40" class="slide-up" layout="column"
    ng-repeat="channel in channels | orderBy: 'number' | filter: queryname"
    ng-if="channel.hasCategory"
    ng-init="channel.edit = false">
  <md-card-header ng-show="channel.edit == false">
    <img ng-src="{{channel.logo}}" alt="">
  </md-card-header>
  <md-card-header-text ng-show="channel.edit == false">
    <span class="md-subhead dark-blue" layout="row" layout-align="center" layout-margin>{{channel.number}}</span>
  </md-card-header-text>
</md-card>

应该更有效率.

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