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How to Dynamically Create a Component in Angular

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How to Dynamically Create a Component in Angular

Follow along with this interesting tutorial to learn how you can dynamically create and load a component in your web app using the Angular framework.

· Web Dev Zone ·
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In this article, we will learn to create a component dynamically. You may need to load a component dynamically in various scenarios, such as wanting to show a popup modal.

Let us assume that we have a component as listed below, which we will load dynamically.

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

@Component({
    selector: 'app-message',
    template: `<h2>{{message}}</h2>
`
})
export class MessageComponent {
    @Input() message: string;
}

To load MessageComponent dynamically you need a container. Let us say that we want to load MessageComponent inside AppComponent. We need a container element in the AppComponent.

The template for AppComponent is as below:

<div style="text-align:center">
     <h1>
         Welcome to {{ title }}!
     </h1>
     <template #messagecontainer>
     </template>
 </div>

As you can see, we have an entry point template or a container template in which we will load MessageComponent dynamically.

In AppComponent, we need to import the following:

  1.  ViewChildViewContainerRef, and ComponentFactoryResolver from @angular/core. 
  2.  ComponentRef and ComponentFactory from @angular/core. 
  3.  MessageComponent from message.component.

After importing the required elements, AppComponent will look like the following code block:

import {
    Component,
    ViewChild,
    ViewContainerRef,
    ComponentFactoryResolver,
    ComponentRef,
    ComponentFactory
} from '@angular/core';
import { MessageComponent } from './message.component';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html'
})
export class AppComponent {
    title = 'app';
}

We can access template using ViewChild inside the Component class. The template is a container in which we want to load the component dynamically. Therefore, we have to access template with ViewConatinerRef.

ViewContainerRef represents a container where one or more views can be attached. This can contain two types of views.

Host Views are created by instantiating a component using createComponent and Embedded Views are created by instantiating an Embedded Template usingcreateEmbeddedView. We will use Host Views to dynamically load MessageComponent.

Let us create a variable called entry which will refer to the template element. In addition, we have injected ComponentFactoryResolver services to the component class, which will be needed to dynamically load the component.

export class AppComponent {
    title = 'app';
    @ViewChild('messagecontainer', { read: ViewContainerRef }) entry: ViewContainerRef;
    constructor(private resolver: ComponentFactoryResolver) { }
}

Keep in mind that the entryvariable, which is a reference to a template element, has an API to create components, destroy components, etc.

To create a component, let us first create a function. Inside the function, we need to perform the following tasks:

  • Clear the container.
  • Create a factory for MessageComponent.
  • Create a component using the factory.
  • Pass the value for @Input properties using a component reference instance method.

Putting everything together, the createComponent function will look like the below code:

createComponent(message) {
    this.entry.clear();
    const factory = this.resolver.resolveComponentFactory(MessageComponent);
    const componentRef = this.entry.createComponent(factory);
    componentRef.instance.message = message;
}

We can call the createComponent function on click event attached to the button. Let us put two buttons in the template and call the createComponent function when a button is clicked.

In the output, you can see that component is getting loaded dynamically on the click of the button.

As you click on the buttons, the component will be reloaded with a different message. You can destroy a component using the destroy method on the componentRef.

destroyComponent() {
    this.componentRef.destroy();
}

You can either destroy a dynamically loaded component by manually calling the function or by putting it inside the ngOnDestroy() lifecycle hook of the component so that when the host component is destroyed, the dynamically loaded component will also be destroyed.

Putting everything together, AppComponent will look like the code below:

import {
    Component,
    ViewChild,
    ViewContainerRef,
    ComponentFactoryResolver,
    ComponentRef,
    ComponentFactory
} from '@angular/core';
import { MessageComponent } from './message.component';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html'
})
export class AppComponent {
    title = 'app';
    componentRef: any;

    @ViewChild('messagecontainer', { read: ViewContainerRef }) entry: ViewContainerRef;
    constructor(private resolver: ComponentFactoryResolver) { }

    createComponent(message) {
        this.entry.clear();
        const factory = this.resolver.resolveComponentFactory(MessageComponent);
        this.componentRef = this.entry.createComponent(factory);
        this.componentRef.instance.message = message;
    }
    destroyComponent() {
        this.componentRef.destroy();
    }
}

At this point, when running the application, you will get an error because we have not set the entryComponents in AppModule. We can set that as shown in the listing below:

import { AppComponent } from './app.component';
import { MessageComponent } from './message.component';

@NgModule({
    declarations: [
        AppComponent, MessageComponent
    ],
    imports: [
        BrowserModule
    ],
    providers: [],
    bootstrap: [AppComponent],
    entryComponents: [MessageComponent]
})
export class AppModule { }

This is all you need to do to load a component dynamically in Angular.

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Topics:
angular ,web dev ,dynamic component ,web application development

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