我有一个简单的firebase-Query:
<firebase-query
id="query"
app-name="app_name"
path="/users"
data="{{patients}}">
</firebase-query>
是否可能创建一个回调以实时接收用户节点的更新?我阅读了有关观察者的信息,但我不明白如何在模块中使用它。
使用此查询,默认情况下,来自/用户的节点实时更新为"患者"数组。因此,您可以立即使用此信息,而无需编写任何观察者左右,例如在dom-repeat元素中。当更多的节点出现在查询中时,此元素会更新。反正如果要观察此数组以进行更改(然后修改数据(,则需要在类似的属性块中设置一个观察者:
static get properties() {
return {
patients: {
// use only one of these types:Boolean | Number | String | Array | Object,
// in your case i think its an Array
type: Array
// For an Array or Object, you must return it from a function
// (otherwise the array will be defined on the prototype
// and not the instance):
value: function() { return [] },
// other elements need to get informed if the value changes? then add this
// line:
notify: true,
// now set the observer
observer: '_patientsChanged',
},
}
}
// and the observer function itself:
_patientsChanged(newVal, oldVal){
// do whatever you want to do e.g. Log the change of the Variable in the
// Console:
console.log('Variable patients changed: It had this value: ');
console.log(oldVal);
console.log('And now it has this Value:');
console.log(newVal);
}
善意
chwzrlee