Angular PrimeNG Form TriStateCheckbox Events

Angular PrimeNG is an open-source framework with a rich set of native Angular UI components that are used for great styling and this framework is used to make responsive websites with very much ease. In this article, we will learn about TriStateCheckbox Events in Angular PrimeNG.

The TriCheckbox Component allows a user to make a checkbox with three states ie, true, false & null conditions.

Angular PrimeNG Form TriStateCheckbox Events:

• onChange: It is a callback that is fired on value change.

Syntax:

<p-triStateCheckbox 
    label="..." 
    (event)=function()>
</p-triStateCheckbox>

Creating Angular application & module installation:

Step 1: Create an Angular application using the following command.

ng new appname

Step 2: After creating your project folder i.e. appname, move to it using the following command.

cd appname

Step 3: Install PrimeNG in your given directory.

npm install primeng --save
npm install primeicons --save

Project Structure: It will look like the following

Steps to run the application: Run the below command to see the output

ng serve --save

Example 1: Below is the example code that illustrates the use of Angular PrimeNG TriStateCheckbox Events. In this article, we will learn about onChange function.

• app.component.html:

HTML

<h1 style="color: green;">GeeksforGeeks</h1>
<h2>Angular PrimeNG TriStateCheckbox Events</h2>

<p-triStateCheckbox
    label="TriStateCheckbox Events"
    (onChange)="onChange()">
</p-triStateCheckbox>

• app.component.ts:

Javascript

import { Component } from "@angular/core";

@Component({
    selector: "app-root",
    templateUrl: "./app.component.html"
})

export class AppComponent {
    onChange() {
        alert("Hi Geek!! I am called");
    }
}

• app.module.ts:

Javascript

import { NgModule } from "@angular/core";
import { BrowserModule } from "@angular/platform-browser";
import { FormsModule } from "@angular/forms";
import { BrowserAnimationsModule }
    from "@angular/platform-browser/animations";
import { AppComponent } from "./app.component";
import { TriStateCheckboxModule } from "primeng/tristatecheckbox";

@NgModule({
    imports: [
        BrowserModule,
        BrowserAnimationsModule,
        TriStateCheckboxModule,
        FormsModule
    ],
    declarations: [AppComponent],
    bootstrap: [AppComponent]
})

export class AppModule {}

Output:

Example 2: Below is another example code that illustrates the use of Angular PrimeNG TriStateCheckbox Events. onChange events won’t work when we make TriCheckbox readonly. We will demonstrate this in the below example.

• app.component.html:

HTML

<h1 style="color: green;">GeeksforGeeks</h1>
<h2>Angular PrimeNG TriStateCheckbox Events</h2>

<p-triStateCheckbox
    [readonly]="true"
    label="I am read only"
    (onChange)="onChange()">
</p-triStateCheckbox>

• app.component.ts:

Javascript

import { Component } from "@angular/core";

@Component({
    selector: "app-root",
    templateUrl: "./app.component.html"
})

export class AppComponent {
    onChange() {
        alert("Hi Geek!! I am called");
    }
}

• app.module.ts:

Javascript

import { NgModule } from "@angular/core";
import { BrowserModule } from "@angular/platform-browser";
import { FormsModule } from "@angular/forms";
import { BrowserAnimationsModule }
    from "@angular/platform-browser/animations";
import { AppComponent } from "./app.component";
import { TriStateCheckboxModule } from "primeng/tristatecheckbox";

@NgModule({
    imports: [
        BrowserModule,
        BrowserAnimationsModule,
        TriStateCheckboxModule,
        FormsModule
    ],
    declarations: [AppComponent],
    bootstrap: [AppComponent]
})

export class AppModule {}

Output:

Reference: http://primefaces.org/primeng/tristatecheckbox