angular - 模板更改@Prop() 检测

Question

我如何检测模板中的 Prop 变化， Angular 是这样的:

但我不知道如何在模板中。

import { Component, Input, OnInit } from '@angular/core';

@Component({
  selector: 'my-name',
  template: `
      <h2>First name: {{name}} ({{_name}})</h2>
  `,
})
export class ChildComponent implements OnInit {
  private _name: string;
  constructor() {}

  get name(): string {
    // transform value for display
    return this._name.toUpperCase();
  }

  @Input()
  set name(name: string) {
    console.log('prev value: ', this._name);
    console.log('got name: ', name);
    this._name = name;
  }

  ngOnInit() {
    console.log('on init');
    console.log(this._name);
  }
}

我需要检测属性变化

Answer 1

您可以在属性更改时触发的方法上使用 @Watch 装饰器。

@Watch('name') 
onNameChanged(newValue: string, oldValue: string) {
  this._name = newValue;
}

Note on @Watch: this decorator only trigger on prop changed, it means the onNameChanged() method won't be called the first time that prop is set. In order to intercept the first set, you have to use the componentWillLoad() hook.

componentWillLoad(){
  this.onNameChanged(this.name);
}

工作示例:

import { Component, Prop, Watch } from '@stencil/core';

@Component({
  tag: 'my-name'
})
export class ChildComponent {

  private _name: string;

  @Prop() name: string = '';

  @Watch('name')
  onNameChanged(name: string) {
    console.log('prev value: ', this._name);
    console.log('got name: ', name);
    this._name = name.toUpperCase();
  }

  componentWillLoad(){
    this.onNameChanged(this.name);
  }

  render() {
    return (<h2>First name: {this.name} ({this._name})</h2>);
  }
}