ng-options属性可以在表达式中使用数组或对象来自动生成一个select中的option列表。ng-options与ng-repeat很相似，很多时候可以用ng-repeat来代替ng-options。但是ng-options提供了一些好处，例如减少内存提高速度，以及提供选择框的选项来让用户选择。当select中一个选项被选择，该选项将会被绑定到ng-model。如果你想设一个默认值，可以像这样：$scope.selected = $scope.collection[3]。
之前一直在用ng-repeat就见到过track by，没有去了解它的用法，这次了解了一下。track by主要是防止值有重复，angularjs会报错。因为angularjs需要一个唯一值来与生成的dom绑定，以方便追踪数据。例如：items=[“a”,“a”,“b”],这样ng-repeat=“item in items”就会出错，而用ng-repeat=“(key,value) in items track by key”就不会出现错误了。
ng-options一般有以下用法：
对于数组：
- label for value in array
- select as label for value in array
- label group by group for value in array
- label disable when disable for value in array
- label group by group for value in array track by trackexpr
- label disable when disable for value in array track by trackexpr
- label for value in array | orderBy:orderexpr track by trackexpr(for including a filter with track by)
- 对于对象：
- label for (key , value) in object
- select as label for (key ,value) in object
- label group by group for (key,value) in object
- label disable when disable for (key, value) in object
- select as label group by group for(key, value) in object
- select as label disable when disable for (key, value) in object
一个简单的例子：
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> <script src="js/angular.js"></script> </head> <body ng-app="selectExample"> <div ng-controller="ExampleController"> <ul> <li ng-repeat="color in colors"> <label>Name: <input ng-model="color.name"></label> <label><input type="checkbox" ng-model="color.notAnOption"> Disabled?</label> <button ng-click="colors.splice($index, 1)" aria-label="Remove">X</button> </li> <li> <button ng-click="colors.push({})">add</button> </li> </ul> <hr/> <label>Color (null not allowed): <select ng-model="myColor" ng-options="color.name for color in colors"></select> </label><br/> <label>Color (null allowed): <span class="nullable"> <select ng-model="myColor" ng-options="color.name for color in colors"> <option value="">-- choose color --</option> </select> </span></label><br/> <label>Color grouped by shade: <select ng-model="myColor" ng-options="color.name group by color.shade for color in colors"> </select> </label><br/> <label>Color grouped by shade, with some disabled: <select ng-model="myColor" ng-options="color.name group by color.shade disable when color.notAnOption for color in colors"> </select> </label><br/> Select <button ng-click="myColor = { name:'not in list', shade: 'other' }">bogus</button>. <br/> <hr/> Currently selected: {{ {selected_color:myColor} }} <div style="border:solid 1px black; height:20px" ng-style="{'background-color':myColor.name}"> </div> </div> <script type="text/javascript"> angular.module('selectExample', []) .controller('ExampleController', ['$scope', function($scope) { $scope.colors = [ {name:'black', shade:'dark'}, {name:'white', shade:'light', notAnOption: true}, {name:'red', shade:'dark'}, {name:'blue', shade:'dark', notAnOption: true}, {name:'yellow', shade:'light', notAnOption: false} ]; $scope.myColor = $scope.colors[2]; // red }]); </script> </body> </html>