当我想明确清除它时，无法读取未定义的属性“viewContainerRef”

Question

There is a scenario where I want to clear 'viewContainer' on button click but it is showing error

ERROR TypeError: Cannot read property 'viewContainer' of undefined

Please check attached code for better understanding.

Note: In my case, you will see, I've added click event on document.body and also kept directive name as [ngIf](I know this is not the spoiler).

Also, I tried to set this.ngIf = false; in my click's listener but that too generating the same error.

"ERROR TypeError: Cannot set property 'ngIf' of undefined"

Thanks in advance.

app.component.ts

import { Component, TemplateRef, Directive, ViewContainerRef, Input, ElementRef, Renderer, ViewChild, ViewChildren, HostListener } from '@angular/core';


@Component({
  selector: 'my-app',
  template: `
<div *ngIf="val">
  Hello cpIf Directive.
</div>
  `,
  styles: [`h1 { font-family: Lato; }`]
})
export class AppComponent {

  val: boolean = true;

}


@Directive({
  selector: '[ngIf]'
})
export class CpIfDirective {
  constructor(private templateRef: TemplateRef<any>,
    private viewContainer: ViewContainerRef,
    private renderer: Renderer) {
    //this.viewContainer.createEmbeddedView(this.templateRef);
  }

  ngAfterViewInit() {
    //this.viewContainer.createEmbeddedView(this.templateRef);
    this.renderer.listen(document.body, 'click', this.clearView);
  }


  @Input() set ngIf(condition: boolean) {
    if (condition) {
      this.viewContainer.createEmbeddedView(this.templateRef);

    } else {
      this.viewContainer.clear();
    }
  }

  clearView(event: any) {
    this.viewContainer.clear();
    //this.ngIf = false;
  }

} 

app.module.ts

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';

import { AppComponent } from './app.component';
import { HelloComponent, CpIfDirective } from './hello.component';

@NgModule({
  imports: [BrowserModule, FormsModule, ReactiveFormsModule],
  declarations: [AppComponent, HelloComponent, CpIfDirective],
  bootstrap: [AppComponent]
})
export class AppModule { }

Answer 1

You are just not able to access this inside clearView

use this:

this.renderer.listen(document.body, 'click', (event) => {
  // Do something with 'event'
   this.viewContainer.clear();
})

You are not passing this reference to that clearView function

Demo

or pass the container reference to the clearView like this

this.renderer.listen(document.body, 'click', (event) => {
      // Do something with 'event'
      this.clearView(event, this.viewContainer)
})


clearView(event: any, element) {    
    element.clear();
    //this.ngIf = false;
}

Oh yes, most importantly, arrow functions would work without changing anything, sorry I did not thought about this before :)

An arrow function does not create its own this context, so this has its original meaning from the enclosing context.

  clearView = (event: any) => {    
    this.viewContainer.clear();
    //this.ngIf = false;
  }

Ref