What methods are available to pass a variable value between two components in Angular 2?

Question

What methods are available to pass a variable value between two components in Angular 2?

I've been experimenting with Angular2 and recently created a component called appmenu using angular cli.

The code in appmenu.html looks like this:

<ul>
  <li (click)="menuitem1()">Menu Item 1</li>
  <li>Menu Item 2</li>
  <li>Menu Item 3</li>
</ul>

Now, I want to retrieve the value of testvariable in app.component.html. However, I'm unsure about what needs to be done in my app.component.ts.

Here is the content of appmenu.ts:

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

@Component({
  providers: [AppMenuService], // ERROR OCCURS HERE
  selector: 'app-appmenu',
  templateUrl: './appmenu.component.html',
  styleUrls: ['./appmenu.component.css']
})
export class AppmenuComponent implements OnInit {
public testvariable = "1st";
public data: any;
 // constructor(private sharedData: AppMenuService) { }

  ngOnInit() {
   // this.data = this.sharedData.data;
   // console.log(this.data);
  }

  menuitem1(){
    console.log("Menu item 1 clicked");
  }

}

Additionally, here is the code for appmenu.service.ts:

import { Injectable } from '@angular/core';

@Injectable()
export class AppMenuService{
public data: any;
    constructor() {
        this.data = 'Lorem ipsum dolor sit.';
    }
}

A problem arises in appmenu.component.ts where it references providers: [AppMenuService]. The error message says it cannot find the name AppMenuService.

angular typescript

Answer 1

Answer №1

To access a child component in your parent component, you can utilize the @ViewChild annotation like so:

@ViewChild(ChildComponent) childComponent: ChildComponent;

For more information on component communication in Angular, refer to this documentation.

Answer 2

To access a child component in your parent component, you can utilize the @ViewChild annotation like so:

@ViewChild(ChildComponent) childComponent: ChildComponent;

For more information on component communication in Angular, refer to this documentation.

Answer 3

Answer №2

If you are looking to share a variable statically between two components, one way to achieve this is by declaring the variable in a service and then injecting the service to use the variable. For example:

// shared-data.service.ts

export class SharedDataService {
    public data: any;
    constructor() {
        this.data = 'Lorem ipsum dolor sit.';
    }
}

// app.component.ts

@Component({ ... })
export class AppComponent implements OnInit {
    public data: any;

    constructor(private sharedData: SharedDataService) { }

    public ngOnInit() {
        this.data = this.sharedData.data;
    }
}

// app-menu/app-menu.component.ts

@Component({ ... })
export class AppMenuComponent implements OnInit {
    public data: any;

    constructor(private sharedData: SharedDataService) { }

    public ngOnInit() {
        this.data = this.sharedData.data;
    }
}

However, if you need to share data between parent and child components, using @Input and @Output is more common practice. With @Input, you can pass data from parent to child component/directive directly. And with @Output, you can listen to events emitted by the child component. You can learn more about it here.

For example:

// app.component.ts

@Component({
    template: `
        <app-menu
            [someData]="dataForChild"
            (menuClick)="handleMenuClick($event)">
        </app-menu>
    `
})
export class AppComponent implements OnInit {
    public dataForChild: any;

    constructor() { }

    public ngOnInit() {
        this.dataForChild = 'Lorem ipsum dolor sit.'
    }

    public handleMenuClick(itemIndex) {
        console.log(itemIndex);
    }
}

// app-menu/app-menu.component.ts

@Component({
    selector: 'app-menu',
    template: `
        <ul>
            <li (click)="transferMenuClick(1)">Menu item 1</li>
            <li (click)="transferMenuClick(2)">Menu item 2</li>
            <li (click)="transferMenuClick(3)">Menu item 3</li>
        </ul>
    `
})
export class AppMenuComponent implements OnInit {
    @Output('menuClick')
    public menuClick: EventEmitter<number>;

    @Input('someData')
    public someData: any;

    constructor(private sharedData: SharedDataService) {
        this.menuClick = new EventEmitter<number>;
    }

    public ngOnInit() {
        console.log(this.someData);
    }

    public transferMenuClick(itemIndex) {
        this.menuClick.emit(itemIndex);
    }
}

Answer 4

If you are looking to share a variable statically between two components, one way to achieve this is by declaring the variable in a service and then injecting the service to use the variable. For example:

// shared-data.service.ts

export class SharedDataService {
    public data: any;
    constructor() {
        this.data = 'Lorem ipsum dolor sit.';
    }
}

// app.component.ts

@Component({ ... })
export class AppComponent implements OnInit {
    public data: any;

    constructor(private sharedData: SharedDataService) { }

    public ngOnInit() {
        this.data = this.sharedData.data;
    }
}

// app-menu/app-menu.component.ts

@Component({ ... })
export class AppMenuComponent implements OnInit {
    public data: any;

    constructor(private sharedData: SharedDataService) { }

    public ngOnInit() {
        this.data = this.sharedData.data;
    }
}

However, if you need to share data between parent and child components, using @Input and @Output is more common practice. With @Input, you can pass data from parent to child component/directive directly. And with @Output, you can listen to events emitted by the child component. You can learn more about it here.

For example:

// app.component.ts

@Component({
    template: `
        <app-menu
            [someData]="dataForChild"
            (menuClick)="handleMenuClick($event)">
        </app-menu>
    `
})
export class AppComponent implements OnInit {
    public dataForChild: any;

    constructor() { }

    public ngOnInit() {
        this.dataForChild = 'Lorem ipsum dolor sit.'
    }

    public handleMenuClick(itemIndex) {
        console.log(itemIndex);
    }
}

// app-menu/app-menu.component.ts

@Component({
    selector: 'app-menu',
    template: `
        <ul>
            <li (click)="transferMenuClick(1)">Menu item 1</li>
            <li (click)="transferMenuClick(2)">Menu item 2</li>
            <li (click)="transferMenuClick(3)">Menu item 3</li>
        </ul>
    `
})
export class AppMenuComponent implements OnInit {
    @Output('menuClick')
    public menuClick: EventEmitter<number>;

    @Input('someData')
    public someData: any;

    constructor(private sharedData: SharedDataService) {
        this.menuClick = new EventEmitter<number>;
    }

    public ngOnInit() {
        console.log(this.someData);
    }

    public transferMenuClick(itemIndex) {
        this.menuClick.emit(itemIndex);
    }
}

What methods are available to pass a variable value between two components in Angular 2?

Answer №1

Answer №2

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