javascript - How to pass multiple parameter to @Directives (@Components) in Angular with TypeScript?

Question

Since I've created @Directive as SelectableDirective, I'm little bit confused, about how to pass more than one value to the custom directive. I have searched a lot but didn't get proper solution in Angular with Typescript.

Here is what my sample code is:

Parent Component as MCQComponent:

import { Component, OnInit } from '@angular/core';
import { Question } from '../question/question';
import { AppService } from '../app.service/app.service';
import { SelectableDirective } from '../selectable.directive/selectable.directive';
import { ResultComponent } from '../result-component/result.component';

@Component({
    selector: 'mcq-component',
    template: "
         .....
        <div *ngIf = 'isQuestionView'>
            <ul>
                <li *ngFor = 'let opt of currentQuestion.options' 
                    [selectable] = 'opt'
                    (selectedOption) = 'onOptionSelection($event)'>
                    {{opt.option}}
                </li>
            </ul>
            .....
        </div>

    "
    providers: [AppService],
    directives: [SelectableDirective, ResultComponent]
})
export class MCQComponent implements OnInit{
    private currentIndex:any = 0;
    private currentQuestion:Question = new Question();
    private questionList:Array<Question> = [];
    ....
    constructor(private appService: AppService){}
    ....
}

This is a parent component having custom directive [selectable] which takes one param called opt.

Here is the code for this directive:

import { Directive, HostListener, ElementRef, Input, Output, EventEmitter } from '@angular/core'
import { Question } from '../question/question';

@Directive({
    selector: '[selectable]'
})
export class SelectableDirective{
    private el: HTMLElement;
    @Input('selectable') option:any;

    ...
}

So here I want to pass more parameters from parent component, how do I achieve this?

Answer 1

From the Documentation

As with components, you can add as many directive property bindings as you need by stringing them along in the template.

Add an input property to HighlightDirective called defaultColor:

@Input() defaultColor: string;

Markup

<p [myHighlight]="color" defaultColor="violet">
  Highlight me too!
</p>

Angular knows that the defaultColor binding belongs to the HighlightDirective because you made it public with the @Input decorator.

Either way, the @Input decorator tells Angular that this property is public and available for binding by a parent component. Without @Input, Angular refuses to bind to the property.

For your example

With many parameters

Add properties into the Directive class with @Input() decorator

@Directive({
    selector: '[selectable]'
})
export class SelectableDirective{
    private el: HTMLElement;

    @Input('selectable') option:any;   
    @Input('first') f;
    @Input('second') s;

    ...
}

And in the template pass bound properties to your li element

<li *ngFor = 'let opt of currentQuestion.options' 
    [selectable] = 'opt' 
    [first]='YourParameterHere'
    [second]='YourParameterHere'
    (selectedOption) = 'onOptionSelection($event)'>
    {{opt.option}}
</li>

Here on the li element we have a directive with name selectable. In the selectable we have two @Input()'s, f with name first and s with name second. We have applied these two on the li properties with name [first] and [second]. And our directive will find these properties on that li element, which are set for him with @Input() decorator. So selectable, [first] and [second] will be bound to every directive on li, which has property with these names.

With single parameter

@Directive({
    selector: '[selectable]'
})
export class SelectableDirective{
    private el: HTMLElement;

    @Input('selectable') option:any;   
    @Input('params') params;

    ...
}

Markup

<li *ngFor = 'let opt of currentQuestion.options' 
    [selectable] = 'opt' 
    [params]='{firstParam: 1, seconParam: 2, thirdParam: 3}'
    (selectedOption) = 'onOptionSelection($event)'>
    {{opt.option}}
</li>