Typescript 有没有办法从 Angular 的组件中判断 @Output 连线

发布于05月26日

在组件的ngOnInit方法中，@Input个值将被绑定，因此您可以判断组件上的那些属性，但似乎没有办法判断@Output个事件绑定.我想知道@Output是否连接在组件上.

(使用Angular 和字体)

import {Component, Output, EventEmitter} from '@angular/core';

@Component({
    selector: 'sample',
    template: `<p>a sample</p>`
})
export class SampleComponent {
    @Output() cancel = new EventEmitter();
    
    ngOnInit() {
        // would like to check and see if cancel was used
        // on the element <sample (cancel)="doSomething()"></sample> 
        // or not <sample></sample>
    }
}

推荐答案

方法与user1448982相同，但不使用ObservableWrapper，ObservableWrapper是指不通过api公开使用的平台代码.

(Using Angular 2 RC1 and TypeScript)
Note: This only started working from 2.0.0-beta.16 and greater

import {Component, Output, EventEmitter} from '@angular/core';

@Component({
    selector: 'sample',
    template: `<p>a sample</p>`
})
export class SampleComponent {
    @Output() cancel = new EventEmitter();
    private isCancelUsed = false;

    ngOnInit() {
        this.isCancelUsed = this.cancel.observers.length > 0;
    }
}

Plunker

ObservableWrapper.hasSubscribers方法在内部执行这一行，所以您可以在这里执行相同的操作.

When using TypeScript you will get a transpile time error if Angular ever ends up changing the 100 from a 101 (which is part 102, thus the 103 property).