Let's consider a more realistic and generic use case for *ngTemplateOutlet with ng-container in an Angular application.

Use Case: Dynamic Form Field Rendering

Imagine you are building a dynamic form where the fields can change based on the type of form being filled out. For example, you might have different templates for text input, date input, and select dropdowns. Using *ngTemplateOutlet with ng-container, you can dynamically render the appropriate form field template based on the field type.

Example: Dynamic Form Fields

Parent Component Template (dynamic-form.component.html)

<form>
  <div *ngFor="let field of formFields">
    <ng-container *ngTemplateOutlet="getTemplate(field); context: { $implicit: field }"></ng-container>
  </div>

  <!-- Define the templates -->
  <ng-template #textInput let-field>
    <div class="form-group">
      <label>{{ field.label }}</label>
      <input type="text" [formControlName]="field.name" class="form-control">
    </div>
  </ng-template>

  <ng-template #dateInput let-field>
    <div class="form-group">
      <label>{{ field.label }}</label>
      <input type="date" [formControlName]="field.name" class="form-control">
    </div>
  </ng-template>

  <ng-template #selectInput let-field>
    <div class="form-group">
      <label>{{ field.label }}</label>
      <select [formControlName]="field.name" class="form-control">
        <option *ngFor="let option of field.options" [value]="option.value">{{ option.label }}</option>
      </select>
    </div>
  </ng-template>
</form>

Parent Component Class (dynamic-form.component.ts)

import { Component, TemplateRef, ViewChild } from '@angular/core';
import { FormBuilder, FormGroup } from '@angular/forms';

@Component({
  selector: 'app-dynamic-form',
  templateUrl: './dynamic-form.component.html',
  styleUrls: ['./dynamic-form.component.scss']
})
export class DynamicFormComponent {
  @ViewChild('textInput') textInput!: TemplateRef<any>;
  @ViewChild('dateInput') dateInput!: TemplateRef<any>;
  @ViewChild('selectInput') selectInput!: TemplateRef<any>;

  form: FormGroup;
  formFields = [
    { type: 'text', name: 'firstName', label: 'First Name' },
    { type: 'date', name: 'birthDate', label: 'Birth Date' },
    { type: 'select', name: 'gender', label: 'Gender', options: [
      { value: 'male', label: 'Male' },
      { value: 'female', label: 'Female' }
    ]}
  ];

  constructor(private fb: FormBuilder) {
    this.form = this.fb.group({
      firstName: [''],
      birthDate: [''],
      gender: ['']
    });
  }

  getTemplate(field: any): TemplateRef<any> {
    switch (field.type) {
      case 'text':
        return this.textInput;
      case 'date':
        return this.dateInput;
      case 'select':
        return this.selectInput;
      default:
        throw new Error('Unknown field type');
    }
  }
}

Explanation

1. Templates Definition:

   • Three templates are defined in the parent component's template using <ng-template>: textInput, dateInput, and selectInput.
   • Each template corresponds to a different type of form field and contains the appropriate HTML structure.

2. Dynamic Template Selection:

   • The getTemplate method in the parent component class returns the appropriate template based on the field's type.
   • The *ngTemplateOutlet directive is used within an ng-container to dynamically insert the selected template into the DOM.
   • The context property is used to pass the field data to the template.

3. Rendering Form Fields:

   • The *ngFor directive iterates over the list of form fields.
   • For each field, the ng-container with *ngTemplateOutlet dynamically inserts the appropriate template based on the field's type.

Summary

• Use Case: Dynamic form field rendering based on field type.
• Templates: Define multiple templates using <ng-template> for different types of form fields.
• Dynamic Template Selection: Use *ngTemplateOutlet with ng-container to dynamically insert the selected template.
• Context: Pass data to the template using the context property.

Explanation

If asked about a practical use case for *ngTemplateOutlet with ng-container in an interview, you can explain:

"In a scenario where we need to render different form fields based on the type of field, such as text input, date input, and select dropdowns, we can use *ngTemplateOutlet with ng-container. This allows us to define multiple templates for different field types and dynamically insert the appropriate template based on the field's type. By using the context property, we can pass data to the template, making it a powerful tool for dynamic form rendering in Angular."

This explanation demonstrates your understanding of the concept and provides a clear, practical example of its use.