README.md

In-Out Example

This example shows how to connect two unrelated components — a list and an editor — without either knowing about the other. It introduces ng-xtend's output system, which lets you react to user interactions inside a rendered component (like selecting an item from a list).

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Step 1: Listen to list selection

In the template (src/in-out-display/in-out-display.html), bind to the (outputs) event on the list <xt-render>:

<xt-render displayMode="LIST_VIEW" valueType="bookType"
           [value]="elementsToDisplay()"
           (outputs)="outputChanged($event)">
</xt-render>

The (outputs) emitter fires whenever the rendered component emits an event. The payload is an XtComponentOutput object containing named observables — most importantly valueSelected, which fires when the user selects an item.

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Step 2: Forward selection to the editor

In src/in-out-display/in-out-display.ts:

outputChanged(newValue: XtComponentOutput | null) {
  if (newValue?.valueSelected != null) {
    newValue.valueSelected.subscribe(selected => {
      this.selectedEntity.set(selected);
      this.updateBookForm();
      this.selectedEntityIndex = this.elementsToDisplay().indexOf(selected);
    });
  }
}

Why subscribe instead of a direct value? The output system uses observables because XtRenderComponent dynamically instantiates child components. The valueSelected observable emits every time the selection changes (click a different row, deselect, etc.). Subscribing gives you a stream of selection changes.

updateBookForm() then rebuilds the edit form with the selected entity's data:

protected updateBookForm() {
  const newForm = this.formBuilder.group({});
  updateFormGroupWithValue(newForm, this.selectedEntity() ?? {},
    'bookType', this.resolver.typeResolver);
  this.bookForm.set(newForm);
}

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Step 3: Create and save with form management

The form now supports both create and update via the same form:

<form [formGroup]="bookForm()" (ngSubmit)="saveBook()">
  <xt-render displayMode="FULL_EDITABLE" valueType="bookType"
             [formGroup]="bookForm()"> </xt-render>
  <p-button label="Save" type="submit" />
</form>

createBook() sets selectedEntity to an empty object, clearing the form for a new entry. saveBook() distinguishes create from update by checking selectedEntityIndex: if -1, it appends a new book; otherwise it replaces the existing entry in the array.

Key change from the typed example: The form is now a signal<FormGroup> rather than a plain FormGroup, because it needs to be rebuilt each time the selection changes. The bookForm signal is swapped out via bookForm.set(newForm).

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Summary

Concept	What changes
(outputs) binding	Listen to events from rendered components
valueSelected	Observable that fires when the user picks an item from the list
Two-way data flow	List selection → form population → save updates the list
signal<FormGroup>	Form needs to be reactive because it is rebuilt dynamically
Create vs update	Same form handles both; distinguished by index

What's next?

Example	What it adds
Store Example	Persist books via an API using xt-store instead of an in-memory array
Advanced Type Example	Reference authors from books with a MANY-TO-ONE relation
Dynamic Plugin Example	Load plugins at runtime from a remote server instead of bundling them