原因及現(xiàn)象
我們可以使用ng-repeat指令遍歷一個(gè)JavaScript數(shù)組，當(dāng)數(shù)組中有重復(fù)元素的時(shí)候,AngularJS會(huì)報(bào)錯(cuò):
Error: [ngRepeat:dupes] Duplicates in a repeater are not allowed. Use 'track by' expression to specify unique keys. Repeater: user in users, Duplicate key: number:1。下面的代碼就會(huì)報(bào)錯(cuò)：
<html>
<head>
<script src="angular-1.2.2/angular.js"></script>
<script>
function rootController($scope,$rootScope,$injector)
{
$scope.dataList = [1,2,1];
}
</script>
</head>
<body ng-app ng-controller="rootController">
<div ng-repeat="data in dataList">
{{data}}
</div>
</body>
</html>
這是因?yàn)閚g-Repeat不允許collection中存在兩個(gè)相同Id的對(duì)象。
For example: item in items is equivalent to item in items track by $id(item). This implies that the DOM elements will be associated by item identity in the array.
對(duì)于數(shù)字或者字符串等基本數(shù)據(jù)類型來說，它的id就是它自身的值。因此數(shù)組中是不允許存在兩個(gè)相同的數(shù)字的。為了規(guī)避這個(gè)錯(cuò)誤，需要定義自己的track by表達(dá)式。
// 業(yè)務(wù)上自己生成唯一的iditem in items track by item.id
//或者直接拿循環(huán)的索引變量$index來用item in items track by $index
如果是javascript對(duì)象類型數(shù)據(jù)，那么就算內(nèi)容一摸一樣，ng-repeat也不會(huì)認(rèn)為這是相同的對(duì)象。如果將上面的代碼中dataList，那么是不會(huì)報(bào)錯(cuò)的。比如$scope.dataList = [{"age":10},{"age":10}];
解決辦法
- 在循環(huán)的數(shù)組后面加上 track by $index 即可以完美解決
<li ng-repeat="x in names track by $index">
