如何监听来自类属性 TypeScript 的值变化 - Angular [英] How to listen for value changes from class property TypeScript - Angular

问题描述

在 AngularJS 中，我们可以使用 $watch、$digest... 来监听变量的变化，这在新版本的 Angular (5, 6) 中不再可能.

在 Angular 中，此行为现在是组件生命周期的一部分.

我查看了官方文档、文章，尤其是 Angular 5 更改检测在可变对象上，了解如何在 TypeScript 类/Angular

今天的提议是:

import { OnChanges, SimpleChanges, DoCheck } from '@angular/core';@成分({选择器:'my-comp'，templateUrl: 'my-comp.html',styleUrls: ['my-comp.css'],输入:['输入1'，'输入2']})导出类 MyClass 实现 OnChanges、DoCheck、OnInit{//我可以跟踪这个属性的变化@Input() input1:string;@Input() input2:string;//我想要跟踪的属性！myProperty_1:布尔值myProperty_2: ['A', 'B', 'C'];myProperty_3:MysObject；构造函数(){}ngOnInit() { }//解决方案 1 - 当 Angular 检测到 @Input 属性发生变化时触发ngOnChanges(更改:SimpleChanges){//改变动作}//解决方案 2 - Angular 无法检测到输入属性的更改//DoCheck 允许我们实现自定义更改检测ngDoCheck() {//改变动作}}

这仅适用于 @Input() 属性！

如果我想跟踪组件自身属性(myProperty_1、myProperty_2 或 myProperty_3)的更改，这将不起作用.

有人可以帮我解决这个问题吗?最好是与 Angular 5 兼容的解决方案

解决方案

您仍然可以通过 DoCheck lifehook 通过 KeyValueDiffers 检查组件的字段成员值变化.

import { DoCheck, KeyValueDiffers, KeyValueDiffer } from '@angular/core';不同:KeyValueDiffer;构造函数(私有不同:KeyValueDiffers){this.differ = this.differs.find({}).create();}ngDoCheck() {const change = this.differ.diff(this);如果(改变){change.forEachChangedItem(item => {console.log('项目已更改', 项目);});}}

参见演示.

In AngularJS, we can listen variable change using $watch, $digest... which is no longer possible with the new versions of Angular (5, 6).

In Angular, this behaviour is now part of the component lifecycle.

I checked on the official documention, articles and especially on Angular 5 change detection on mutable objects, to find out how to listen to a variable (class property) change in a TypeScript class / Angular

What is proposed today is :

import { OnChanges, SimpleChanges, DoCheck } from '@angular/core';


@Component({
  selector: 'my-comp',
  templateUrl: 'my-comp.html',
  styleUrls: ['my-comp.css'],
  inputs:['input1', 'input2']
})
export class MyClass implements OnChanges, DoCheck, OnInit{

  //I can track changes for this properties
  @Input() input1:string;
  @Input() input2:string;
  
  //Properties what I want to track !
  myProperty_1: boolean
  myProperty_2: ['A', 'B', 'C'];
  myProperty_3: MysObject;

  constructor() { }

  ngOnInit() { }

  //Solution 1 - fired when Angular detects changes to the @Input properties
  ngOnChanges(changes: SimpleChanges) {
    //Action for change
  }

  //Solution 2 - Where Angular fails to detect the changes to the input property
  //the DoCheck allows us to implement our custom change detection
  ngDoCheck() {
    //Action for change
  }
}

This is only true for @Input() property !

If I want to track changes of my component's own properties (myProperty_1, myProperty_2 or myProperty_3), this will not work.

Can someone help me to solve this problematic ? Preferably a solution that is compatible with Angular 5

解决方案

You can still check component's field members value change by KeyValueDiffers via DoCheck lifehook.

import { DoCheck, KeyValueDiffers, KeyValueDiffer } from '@angular/core';

differ: KeyValueDiffer<string, any>;
constructor(private differs: KeyValueDiffers) {
  this.differ = this.differs.find({}).create();
}

ngDoCheck() {
  const change = this.differ.diff(this);
  if (change) {
    change.forEachChangedItem(item => {
      console.log('item changed', item);
    });
  }
}

see demo.

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