.property（）有什么作用？在function（）{}。property（）中 [英] What does .property() do? in function(){}.property()

问题描述

Todos.TodoController = Ember.ObjectController.extend({
  isCompleted: function(key, value){
    var model = this.get('model');

    if (value === undefined) {
      // property being used as a getter
      return model.get('isCompleted');
    } else {
      // property being used as a setter
      model.set('isCompleted', value);
      model.save();
      return value;
    }
  }.property('model.isCompleted')
});

我正在使用Ember.js的ToDo指南，但似乎无法理解该控制器有效。 .property（）是什么意思？而当我删除返回值行时，功能如何保持不变。如果有人可以确切解释这里发生的事情，那将是很好的。

I'm working through the ToDo guide for Ember.js and I can't seem to understand how this controller works. What does the .property() mean? And how come when I remove the 'return value;' line the functionality stays the same. If someone could explain exactly what's going on here that would be great.

链接至指南：http://emberjs.com/guides/getting-started/marking-a-model-as-complete-incomplete/

推荐答案

在javascript中，获取或设置一个属性时进行某些处理的唯一方法是使用 Object.defineProperty ：

In javascript the only way to do some processing when getting or setting one property is using Object.defineProperty:

Object.defineProperty(person, "b", {
  get : function() { 
    return person.firstName + ' ' + person.surname; 
  },
  set : function(newValue) {
    var names = newValue.split(' '); 
    person.firsname = names[0];
    person.surname = names[1]; 
  },
  enumerable : true,
  configurable : true
});

但这有一些缺点：

• 不是跨浏览器


• 没有绑定，也就是说，如果 firstname 或姓氏发生更改，相关属性全名保持不变。


• 调用 person.name 当未定义 person 时，抛出错误


• 不可能触发观察者，没有其他代码，也没有意识到依赖等级：名字取决于全名，

• Isn't cross browser
• Doesn't have binding, in other words, if firstname or surname changes, the dependent property fullname isn't changed.
• Calling person.name when person is undefined, make an error to be throwed
• Isn't possible to trigger observers, no without additional code and aware of the depency hierachy: firstname depends from fullname, and it can be dependency of others properties arghhh!

由于这个Ember具有属性的概念，称为计算的属性。

Due to this Ember has the concept of "property", called computed property.

它可以用两种方式声明：

It can be declared in 2 ways:

foo: Ember.computed(function({
  ...
}).property(dependent keys);

或使用（默认） Ember.ENV.EXTEND_PROTOTYPES = true ：

foo: function() {
  ...
}.property(dependent keys);

属性（依赖键）是之所以需要它，是因为它告诉我们改变属性时会改变的属性。

The property(dependent keys), is needed because it tell to ember what is the properies that when changed, will make the property be updated.

fullname: function(key, value) {
  // setter
  if (value !== undefined) {
    var names = value.split(' ');
    this.set('firstname', names[0]);
    this.set('surname', names[1]);
  }
  // always return the complete result, so nexts calls to this.get('fullname') will return the cached value  
  return this.get('firstname') + ' ' + this.get('surname');
}.property('firstname', 'surname')

使用此功能，您可以

• 的优势，当更改名或姓时更改为新值，全名。


• beforeObserves 在更改值之前被触发，而 observs 被触发


• 引用某些属性的任何模板都会更新


• 然后再调用一次person.get（'first''），将会返回一个缓存的值，保存处理。您可以使用 .property（..）。volatile（）


• 禁用此属性，当访问诸如null之类的对象时，请避免null或未定义的错误： controller.get（'person.dog.name'）如果未定义人员或狗，则返回未定义。

• when changing firstname or surname to a new value, fullname is changed.
• The beforeObserves are triggered before changing the value, and the observes are triggered after the value change.
• Any template referencing some property is updated
• More then one call to person.get('firstname'), will return a cached value, saving processing. You can disable this using .property(..).volatile()
• Avoid null or undefined errors, when accessing null objects like: controller.get('person.dog.name') returns undefined, if person or dog is undefined.

我希望对您有所帮助

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