@bindable changeHandler 在绑定完成更新之前触发 [英] @bindable changeHandler fires before bindings are done updating

问题描述

App.js

export class App {
  constructor() {
    this.widgets = [{ name: 'zero'}, {name: 'one'}, {name:'two'}];
    this.shipment = { widget: this.widgets[1] };
  }
}

App.html

<template>
  <require from="./widget-picker"></require>
  <require from="./some-other-component"></require>

  <widget-picker widget.bind="shipment.widget" widgets.bind="widgets"></widget-picker>
  <some-other-component widget.bind="shipment.widget"/>
</template>

widget-picker.js

import {bindable, bindingMode} from 'aurelia-framework';

export class WidgetPicker {
  @bindable({ defaultBindingMode: bindingMode.twoWay, changeHandler: 'widgetChanged'  }) 
  widget;

  @bindable widgets;

  widgetChanged(widget) {
      // Use an Event Aggregator to send a message to SomeOtherComponent
      // to say that they should check their widget binding for updates.
  }
}

widget-picker.html

<select value.bind="widget">
  <option repeat.for="widget of widgets" model.bind="widget">${widget.name}</option>
</select>

问题:

@bindable 的 changeHandler 在绑定更新到 App.js 及其 this.shipment.widget 之前触发 widgetChanged 事件.

The Problem:

The @bindable's changeHandler fires the widgetChanged event before the binding gets updated to App.js and its this.shipment.widget.

所以当 Event Aggregator 消息出去时，之前的值仍然设置在 `this.shipment.widget' 上.

So when the Event Aggregator message goes out, the previous value is still set on `this.shipment.widget'.

有没有办法让 @bindable 的 changeHandler 等到所有要为 @bindable 更新的绑定完成?

Is there a way to make @bindable's changeHandler wait until all the bindings that will be updated for @bindable are done?

或者我可以使用另一个回调吗?也许是一个 changedHandler(过去时)?

Or is there another callback I can use? Maybe a changedHandler (past tense)?

我确实尝试将 change.delegate="widgetChanged" 添加到 select 中，希望 delegate 选项会使其变慢，但它仍然会在更新完全推出之前触发.

I did try to add change.delegate="widgetChanged" to the select, hoping that the delegate option would make it slower, but it still fires before the update is fully rolled out.

推荐答案

你可以将需要做的工作推送到微任务队列中:

You could push the work you need to do onto the micro task queue:

import {bindable, bindingMode, inject, TaskQueue} from 'aurelia-framework';

@inject(TaskQueue)
export class WidgetPicker {
  @bindable({ defaultBindingMode: bindingMode.twoWay, changeHandler: 'widgetChanged'  }) 
  widget;
  @bindable widgets;

  constructor(taskQueue) {
    this.taskQueue = taskQueue;
  }

  widgetChanged(widget) {
    this.taskQueue.queueMicroTask(
      () => {
        // Use an Event Aggregator to send a message to SomeOtherComponent
        // to say that they should check their widget binding for updates.
      });
  }
}

这将确保它发生在事件循环的同一个回合"期间(而不是像 setTimeout(...) 那样做).

This will ensure it occurs during the same "turn" of the event loop (as opposed to doing something like setTimeout(...)).

这篇关于@bindable changeHandler 在绑定完成更新之前触发的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！