理解ngRepeat'track by'表达式 [英] Understanding the ngRepeat 'track by' expression

问题描述

我很难理解angularjs中ng-repeat的跟踪表达方式是如何工作的。文档非常稀缺： http://docs.angularjs.org/api/ng/directive / ngRepeat

I'm having difficulties understanding how the track by expression of ng-repeat in angularjs works. The documentation is very scarce: http://docs.angularjs.org/api/ng/directive/ngRepeat

您能解释这两段代码之间的区别在于数据绑定和其他相关方面吗？

Can you explain what the difference between those two snippets of code is in terms of databinding and other relevant aspects?

with： track by $ index

<!--names is an array-->
<div ng-repeat="(key, value) in names track by $index">
  <input ng-model="value[key]">                         
</div>

没有（相同的输出）

<!--names is an array-->
<div ng-repeat="(key, value) in names">
   <input ng-model="value[key]">                         
</div>

推荐答案

您可以跟踪$ index 如果您的数据源有重复的标识符

You can track by $index if your data source has duplicate identifiers

例如： $ scope.dataSource：[{id：1，name ：'one'}，{id：1，name：'one too'}，{id：2，name：'two'}]

使用'id'作为标识符时，您无法迭代此集合（重复ID：1）。

You can't iterate this collection while using 'id' as identifier (duplicate id:1).

将无效：

<element ng-repeat="item.id as item.name for item in dataSource">
  // something with item ...
</element>

但如果使用跟踪$ index ：

<element ng-repeat="item in dataSource track by $index">
  // something with item ...
</element>

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