Angular2 Best way for dynamic component

Question

I would like to know what is the best way (performance) to create dynamic component. I tried both but I'm not able to determine which one I should use.

With an ng-switch in my component.html container

@Component({
  selector: 'app-component-container',
  template: `<div [ngSwitch]="typeComponent">
              <app-component-one *ngSwitchCase="1" [value]="someValue"></app-component-one>
              <app-component-two *ngSwitchCase="2" [value]="someValue"></app-component-two>
              <app-component-three *ngSwitchCase="3" [value]="someValue"></app-component-three>
              </div>`
})
export class ContainerComponent implements OnInit {
  private typeComponent: number;
  private someValue: string;

  constructor() {
    this.typeComponent = 2;
    this.someValue = "Hello";

  }

  ngOnInit() {

  }
}

or with a component builder in my component.ts container

@Component({
  selector: 'app-component-container',
  template: '<div #container></div>'
})
export class ContainerComponent implements OnInit {
  @ViewChild('container', {read: ViewContainerRef}) container: ViewContainerRef;

  private typeComponent: number;

  private someValue: string;

  constructor(private _resolver: ComponentFactoryResolver) {
    this.typeComponent = 2;
    this.someValue = "Hello";
  }

  ngOnInit() {
    let childComponent: ComponentRef<any> = null;
    switch (this.typeComponent) {
      case 1:
        childComponent = this.container.createComponent<ChildComponentOne>(this._resolver.resolveComponentFactory(ChildComponentOne));
        break;
      case 2:
        childComponent = this.container.createComponent<ChildComponentTwo>(this._resolver.resolveComponentFactory(ChildComponentTwo));
        break;
      case 3:
        childComponent = this.container.createComponent<ChildComponentThree>(this._resolver.resolveComponentFactory(ChildComponentThree));
        break;
    }

    if (childComponent != null) {
      childComponent.instance.value = this.someValue;
    }
  }
}

This are simple exemple, in my application I have huge imbrication of dynamic component.

Thank you in advance for your answer guys.

In my second exemple, the cool thing is I can have an instance on my childComponent, I can easily manipulate the instance and call methods. In my opinion this is more OO way. — Soulm8
– Soulm8, Commented Dec 14, 2016 at 16:37

David M. · Accepted Answer · 2016-12-22 13:36:25Z

Although both ways are viable, for the sake of DRYness, readability and future maintenance I would probably go the second way - that is, creating a dynamic component via the API and inserting it as a child of the container...

You can further decrease duplication in your code this way:

ngOnInit() {
  let childComponentType: Type = null;
  switch (this.typeComponent) {
    case 1:
      childComponentType = ChildComponentOne;
      break;
    case 2:
      childComponentType = ChildComponentTwo;
      break;
    case 3:
      childComponentType = ChildComponentThree;
      break;
  }

  if (childComponentType != null) {
    let factory = this._resolver.resolveComponentFactory(childComponentType);
    let instance: ComponentRef<any> = this.container.createComponent(factory);

    childComponent.instance.value = this.someValue;
  }
}

You could also have all of your 3 example components inherit a common base class and have your common attributes, methods and @Outputs in the base class. This way you could read values and subscribe to EventEmitters when each component share a common behaviour.

Something along these lines:

export class ChildComponentBaseClass {
  @Input() value;
}

@Component({...})
export class ChildComponentOne<ChildComponentBaseClass> {
  ...
}
@Component({...})
export class ChildComponentTwo<ChildComponentBaseClass> {
  ...
}

ngOnInit() {
  let childComponentType: Type = null;
  switch (this.typeComponent) {
    case 1:
      childComponentType = ChildComponentOne;
      break;
    case 2:
      childComponentType = ChildComponentTwo;
      break;
    case 3:
      childComponentType = ChildComponentThree;
      break;
  }

  if (childComponentType != null) {
    let factory = this._resolver.resolveComponentFactory(childComponentType);
    let instance: ComponentRef<ChildComponentBaseClass> = this.container.createComponent<ChildComponentBaseClass>(factory);

    // instance.value is now properly typed!
    childComponent.instance.value = this.someValue;
  }
}

A sight improvement to get rid of the verbose switch would be to use a dictionary. const typeToComponentMap = { 1: ChildComponentTwo, 2: ChildComponentTwo, 3: ChildComponentThree }; then use: let factory = this._resolver.resolveComponentFactory(typeToComponentMap[this.typeComponent]);

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