angular学习笔记(十四)-$watch(3)
同样的例子,还可以这样写:
<!DOCTYPE html> <html ng-app> <head> <title>11.3$watch监控数据变化</title> <meta charset="utf-8"> <script src="../angular.js"></script> <script src="script.js"></script> </head> <body> <div ng-controller="CartController"> <h1>your shopping cart</h1> <table> <tr ng-repeat="item in items"> <td>{{item.title}}</td> <td><input ng-model="item.quantity"/></td> <td>{{item.price|currency}}</td> <td class="red">{{item.price*item.quantity|currency}}</td> <td><button ng-click="remove($index)">remove</button></td> </tr> </table> <hr> <table> <tr> <td>总价: <span class="del">{{computeTotal()|currency}}</span></td> </tr> <tr> <td>折扣: <span class="red">{{discount|currency}}</span></td> </tr> <tr> <td>现价: <span class="green">{{computeNow()|currency}}</span></td> </tr> </table> </div> </body> </html>
function CartController ($scope) { $scope.items = [ {"title":"兔子","quantity":1,"price":"100"}, {"title":"喵","quantity":2,"price":"200"}, {"title":"狗只","quantity":1,"price":"400"}, {"title":"仓鼠","quantity":1,"price":"300"} ]; $scope.remove = function(index){ $scope.items.splice(index,1) }; $scope.discount = 0; $scope.computeTotal = function(){ var total = 0; for(var i=0; i<$scope.items.length; i++){ total += $scope.items[i].quantity*$scope.items[i].price; } return total }; $scope.computeDiscount = function(newV,oldV,scope){ $scope.discount = newV >= 500 ? newV*0.1 : 0 ; }; $scope.computeNow = function(){ return $scope.computeTotal() - $scope.discount; }; $scope.$watch('computeTotal()',$scope.computeDiscount); }
/*
最后这句橙色的,也可以写成:
$scope.$watch($scope.computeTotal,$scope.computeDiscount)
效果一致
*/
1. 视图的总价部分,改成computeTotal()
2. $watch监测computeTotal函数返回值的变化
3. 总价变化,则调用computeDiscount函数计算折扣,其中第一个参数就是最新的总价
4. 视图的现价部分,改成computeNow(),通过总价和折扣计算现价
使用这种方法,逻辑上不够清楚,并且,$scope.computeTotal会被多次执行,影响性能,仅作参考.
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遗留问题:
使用angular实现同一个功能,有多种设计方法,需要考虑它的性能,考虑逻辑性.
目前来说,首先要做到的是能够以清楚的逻辑将程序设计出来,将来再慢慢考虑性能.
