从子@Input setter访问提供者方法 - Ionic2 / Angular2 [英] Access a provider method from child @Input setter - Ionic2 / Angular2

问题描述

我正在尝试从我的组件 @Input 方法访问提供程序类。但是，当调用 @Input 方法时似乎提供者不可用

I'm trying to access a provider class from my components @Input method. However it seems like the provider is not available when the @Input method is called

以下是我的代码

#provider
import { Injectable } from '@angular/core';
import 'rxjs/add/operator/map';


@Injectable()
export class MyProvider {

  constructor() {}

  sampleMethod(){
    return 'sample method';
  }
}

#component
import { Component, Input } from '@angular/core';
import {MyProvider} from '../../providers/my-provider/my-provider';
import { NavController} from 'ionic-angular';

@Component({
  selector: 'selected-options',
  templateUrl: 'build/components/selected-options/selected-options.html',
  inputs: ['node']
})
export class SelectedOptions {

  provider: MyProvider;

  @Input()
  set node(n: any){
     this.provider.sampleMethod();    
  }
}

#page (where I call the component) 
<selected-options [node]="node.Name"></selected-options>

所以问题在于行

this.provider.sampleMethod（）;

我得到的错误是原始异常：TypeError：无法读取未定义的属性'sampleMethod'。

所以我相信提供者：MyProvider; 在 @Input 方法。但是如果我在构造函数中使用它，这可以正常工作。
如何在 @Input 方法中访问提供者方法？

So I believe provider: MyProvider; is not loaded when the @Input method is called. But this works fine if I use it inside the constructor. How can I access a provider method inside a @Input method?

推荐答案

这可能听起来很混乱，但是你得到的错误是因为提供程序没有作为参数包含在构造函数中（因此，你的构造函数没有创建<$ c $的实例） c> MyProvider class）。

It may sound confusing, but the error you're getting is because the provider is not being included in the constructor as a parameter (and because of that, your constructor is not creating an instance of the MyProvider class).

请看一下这个plunker 。就像你可以在那里，即使我们在 @Input setter拦截器中使用 myProvider 实例，构造函数已经创建服务的实例，所以你可以毫无问题地调用 sampleMethod（）。

Please take a look at this plunker. Like you can se there, even though we use the myProvider instance in the @Input setter interceptor, the constructor already created the instance of the service, so you can call the sampleMethod() without problems.

import { Component, Input } from "@angular/core";
import { MyProvider } from './my-provider.ts';

@Component({
  templateUrl:"child.html",
  selector: 'child-selector',
  inputs: ['node']
})
export class ChildPage {

  private result: string;

  @Input()
  set node(node: string){
    // Because the provider instance is injected on the constructor, we can
    // call the sampleMethod() here
    node = node + ' from ChildPage';
    this.result = this.myProvider.sampleMethod(node);
  }

  // Injects an instance of the MyProvider class
  constructor(private myProvider: MyProvider) {

  }
}

因此，如果您只需添加私有myProvider：MyProvider 您的构造函数中的参数应该可以正常工作：）

So if you just add the private myProvider: MyProvider parameter in your constructor your code should work fine :)

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