http://plnkr.co/edit/fqsLoxKJtx3NpYxxbCDv

ngRepeat 出来的列表内部都有个 $index，不要为每一个列表项设置 isSelected，而是要针对整个列表跟踪当前被选中的 $index 是哪个，然后用表达式绑定那个 class，判断 $index 是不是 currentSelected 就可以了。

<style type="text/css">
      .selected{
        background-color: lightgreen;
      }
    </style>
  <p ng-repeat="item in items" ng-class='{selected:$index==selectedRow}' ng-click='selectedWhich($index)'>
      <span>{{item.product_name}}</span>
      <span>{{item.price | currency}}</span>
    </p>
   <script>
    $scope.items = [
          { product_name: "Product 1", price: 50 },
          { product_name: "Product 2", price: 20 },
          { product_name: "Product 3", price: 180 }
        ];
        $scope.selectedWhich = function (row) {
          $scope.selectedRow = row;
        }
</script>