Utilizing Angular to pass a component as the ng-template of another component

Question

Utilizing Angular to pass a component as the ng-template of another component

In my Angular 6 application, I am faced with the challenge of passing a Component to another Component as an ng-template. The scenario involves having a Component A that needs to be replicated multiple times, each time with different components (referred to as Component B and Component C) that share the same Inputs.

The template structure for Component A is as follows:

<div class="row-detail-panel">
    <h4 class="row-detail-panel-title">{{ newEntity ? 'Add new' : 'Edit this'}} {{ entityName }}</h4>

    <!--THE COMPONENT TO BE INJECTED-->
    <app-component-b
      [inline]="true"
      [form]="form"
    ></app-component-b>
    <!--END-->

    <!--additional HTML code here-->
  </div>

To create instances of Component A, the following syntax is used:

<app-component-a
    [entity]="row"
    [entityName]="entityName"
  ></app-component-a>

To address this requirement, I decided to utilize ng-template by modifying the Component A template as shown below:

<div class="row-detail-panel">
    <h4 class="row-detail-panel-title">{{ newEntity ? 'Add new' : 'Edit this'}} {{ entityName }}</h4>

    <ng-template></ng-template>

    <!--additional HTML code here-->
  </div>

Instances of Component A can now be created using the following approach:

<app-component-a
    [entity]="row"
    [entityName]="entityName"
  >
    <app-component-b
      [inline]="true"
      [form]="form" <!--ISSUE: "form" is not accessible here-->
    ></app-component-b>
  </app-component-a>

This setup allows for easy injection of Component C instead of Component B within Component A's ng-template:

<app-component-a
    [entity]="row"
    [entityName]="entityName"
  >
    <app-component-c
      [inline]="true"
      [form]="form" <!--ISSUE: "form" is not accessible here-->
    ></app-component-c>
  </app-component-a>

Challenge:

The variable "form" needed for injection into Component B or Component C only exists within Component A and not in its parent (due to specific reasons preventing it from being moved up a level). How can this problem be resolved?

angular typescript angular-components ng-template

Answer 1

Answer №1

If you want to achieve this functionality, here's a solution:

When invoking component A, pass an ng-template to it in the following way:

<app-component-a>
   <ng-template *ngIf=”condition; else elseBlock”>
      <app-component-b></app-component-b>
   </ng-template>
   <ng-template #elseBlock>
      <app-component-c></app-component-c>
   </ng-template>
</app-component-a>

In your app-component-a.ts file, include the following line of code:

@ContentChild(TemplateRef) template: TemplateRef;

This means that the template will display component B or C depending on the condition.

In the template of component A, add the following code:

<ng-container [ngTemplateOutlet]="template"></ng-container>

Now, the ng-container will display Component B or C based on the condition.

If you need to manage forms, one option is to create a service in component A, inject it into components A, B, and C, and share the form through that service.

By including components B and C as shown above, Angular will handle the creation and destruction of these components automatically. Otherwise, if the condition in ng-template changes, component B may not be destroyed when component C is instantiated.

Edit:

Another approach could be to emit (@Output) the form from component A to its parent component on initialization. This way, when components B or C are called, A's parent will have access to the form and can pass it to them.

Answer 2

If you want to achieve this functionality, here's a solution:

When invoking component A, pass an ng-template to it in the following way:

<app-component-a>
   <ng-template *ngIf=”condition; else elseBlock”>
      <app-component-b></app-component-b>
   </ng-template>
   <ng-template #elseBlock>
      <app-component-c></app-component-c>
   </ng-template>
</app-component-a>

In your app-component-a.ts file, include the following line of code:

@ContentChild(TemplateRef) template: TemplateRef;

This means that the template will display component B or C depending on the condition.

In the template of component A, add the following code:

<ng-container [ngTemplateOutlet]="template"></ng-container>

Now, the ng-container will display Component B or C based on the condition.

If you need to manage forms, one option is to create a service in component A, inject it into components A, B, and C, and share the form through that service.

By including components B and C as shown above, Angular will handle the creation and destruction of these components automatically. Otherwise, if the condition in ng-template changes, component B may not be destroyed when component C is instantiated.

Edit:

Another approach could be to emit (@Output) the form from component A to its parent component on initialization. This way, when components B or C are called, A's parent will have access to the form and can pass it to them.

Answer 3

Answer №2

Have you attempted to implement it like this:

<app-component-a #compA
  [entity]="row"
  [entityName]="entityName">
  <app-component-b
    [inline]="true"
    [form]="compA.form"
  ></app-component-b>
</app-component-a>

// component-a.html

<div class="row-detail-panel">
  <h4 class="row-detail-panel-title">{{ newEntity ? 'Add new' : 'Edit this'}} {{ entityName }}</h4>
  <ng-content></ng-content>
</div>

To make this work, ensure that the A component's form member is public and preferably declared as readonly.

Answer 4

Have you attempted to implement it like this:

<app-component-a #compA
  [entity]="row"
  [entityName]="entityName">
  <app-component-b
    [inline]="true"
    [form]="compA.form"
  ></app-component-b>
</app-component-a>

// component-a.html

<div class="row-detail-panel">
  <h4 class="row-detail-panel-title">{{ newEntity ? 'Add new' : 'Edit this'}} {{ entityName }}</h4>
  <ng-content></ng-content>
</div>

To make this work, ensure that the A component's form member is public and preferably declared as readonly.

Utilizing Angular to pass a component as the ng-template of another component

Answer №1

Answer №2

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