md-select不能设置选定的值

Question

我有一个md-select设置如下：

<md-select placeholder="Category" ng-model="current.Category" flex >
    <md-option ng-repeat="item in categories" ng-value="{{item}}">{{item.Name}}</md-option>
</md-select>

@scope.categories值是

[  
{  
  "Name":"Commercial & Industrial",
  "ParentId":null,
  "Categories":[  
     {  
        "Name":"Deceptive Marketing",
        "ParentId":19,
        "Categories":[  

        ],
        "Id":24,
        "ModifiedDate":"2015-08-06T07:49:53.0489545",
        "CreatedDate":"2015-08-06T15:49:51.707"
     },
     {  
        "Name":"Aggressive Agents",
        "ParentId":19,
        "Categories":[  

        ],
        "Id":25,
        "ModifiedDate":"2015-08-06T07:50:10.0026497",
        "CreatedDate":"2015-08-06T15:50:08.63"
     }
  ],
  "Id":19,
  "ModifiedDate":"08/06/2015 @ 7:49AM",
  "CreatedDate":"08/06/2015 @ 3:49PM"
 },
 {  
  "Name":"Competitive Supply",
  "ParentId":null,
  "Categories":[  
     {  
        "Name":"Security Deposit",
        "ParentId":20,
        "Categories":[  

        ],
        "Id":21,
        "ModifiedDate":"2015-08-06T07:49:30.3966895",
        "CreatedDate":"2015-08-06T15:49:25.8"
     },
     {  
        "Name":"Meter",
        "ParentId":20,
        "Categories":[  

        ],
        "Id":22,
        "ModifiedDate":"2015-08-06T07:49:34.6571155",
        "CreatedDate":"2015-08-06T15:49:33.3"
     },
     {  
        "Name":"Bill",
        "ParentId":20,
        "Categories":[  

        ],
        "Id":23,
        "ModifiedDate":"2015-08-06T07:49:41.7268224",
        "CreatedDate":"2015-08-06T15:49:40.357"
     }
  ],
  "Id":20,
  "ModifiedDate":"08/06/2015 @ 7:49AM",
  "CreatedDate":"08/06/2015 @ 3:49PM"
   }
]

md-select运行得很好。但我不知道的是如何设置选择值。当我尝试将模型current.Category设置为来自$scope.categories的一个值时，它不会被设置。

Answer 1

文档并不是明确的，但是您应该使用ng-selected。我创建了一个码页来说明，但基本上：

<md-option ng-repeat="(index,item) in categories" ng-value="{{item}}"
           ng-selected="index == 1">    
    {{item.Name}}
</md-option>

这将选择第二个类别(类别数组中的索引1)。

Answer 2

您需要使用ng-model-options，trackBy并选择一个唯一的模型字段作为选择器：

<md-select placeholder="Category" 
    ng-model="current.Category" 
    ng-model-options="{trackBy: '$value.Id' }" // <-- unique field 'Id'
    flex >
    <md-option 
     ng-repeat="item in categories" 
     ng-value="{{item}}">{{item.Name}}</md-option>
</md-select>

这个解是用角材料的正式文件描述的。

Answer 3

为了设置select的默认值，可以使用ng选定的和ng模型。

    <md-select ng-model="vmIdPage.number">
             <md-option ng-value="mod" ng-repeat="mod in vmIdPage.initObject.listeModaliteMisePlace" ng-selected="{{ mod.id === vmIdPage.number.id ? 'true' : 'false' }}">
                {{mod.libelle}}
             </md-option>
    </md-select>