$ root和$ parent有什么区别？

Question

我正在学习KnockoutJS,但我不明白$root和$parent使用之间的区别.请参阅此jsfiddle,或以下代码:

<div data-bind="foreach:mainloop">
    $data Value: <span data-bind="text:$data.firstName"></span> 
                  <span data-bind="text:$data.lastName"></span> --(1)

    <br/>
    $parent Value: <span data-bind="text:firstName"> </span> 
                   <span data-bind="text:$parent.lastName"></span>
    <br/>
    $root Value: <span data-bind="text:firstName"></span>
                 <span data-bind="text:$root.lastName"></span>
    <br/>
        <hr/>
</div>

var mainLoopModel = function () {
    var self = this; // Root Level scope
    self.mainloop = ko.observableArray([{
        'firstName': 'jhon'
    }, {
        'firstName': 'sam'
    }]);
    self.lastName = ko.observable('peters');
    /*if you remove $data before lastName in note (1) you get undefined error because because mainloop dont have lastName root model has lastName so you have to access using parent or higher level */
}

ko.applyBindings(new mainLoopModel());

在上面的代码中$root,$parent它们都用于相同的目的:引用外部范围变量.我只是想知道它$root和$parent用法之间有什么区别吗？如果是,那么请帮助我理解一个正确使用的好例子.

Answer 1

它们相似但不同:

• $root指的是应用于DOM的视图模型ko.applyBindings;
• $parent 是指直接外部范围;

或者,从视觉$data上看:

或者,用相关文件的话说:

• $parent:这是父上下文中的视图模型对象,即当前上下文之外的视图模型对象.

• $root:这是根上下文中的主视图模型对象,即最顶层的父上下文.它通常是传递给的对象ko.applyBindings.它相当于$parents[$parents.length - 1].

• $data:这是当前上下文中的视图模型对象.在根上下文中,$ data和$ root是等效的.

如果您的视图模型嵌套多个级别,您将只会看到实际的差异,否则它们将达到相同的效果.

它的好处很简单:

var Person = function(name) {
  var self = this;
  self.name = ko.observable(name);
  self.children = ko.observableArray([]);
}
  
var ViewModel = function() {
  var self = this;
  self.name = 'root view model';
  self.mainPerson = ko.observable();
}

var vm = new ViewModel(),
    grandpa = new Person('grandpa'),
    daddy = new Person('daddy'),
    son1 = new Person('marc'),
    son2 = new Person('john');

vm.mainPerson(grandpa);
grandpa.children.push(daddy);
daddy.children.push(son1);
daddy.children.push(son2);

ko.applyBindings(vm);

th, td { padding: 10px; border: 1px solid gray; }

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>

<script type="text/html" id="person">
  <tr>
    <td data-bind="text: $root.name"></td>
    <td data-bind="text: $parent.name"></td>
    <td data-bind="text: $data.name"></td>
  </tr>
  <!-- ko template: { name: 'person', foreach: children } --><!-- /ko -->
</script>

<table>
  <tr>
    <th>$root</th>
    <th>$parent</th>
    <th>$data</th>
  </tr>
  <!-- ko template: { name: 'person', data: mainPerson } --><!-- /ko -->
</table>

该$root是永远不变的.这$parent是不同的,取决于你的嵌套程度.