When using @ContentChildren with a QueryList in Angular, the changes are typically detected automatically. However, there are scenarios where changes might not be detected when passing a TemplateRef through @Input.

One possible reason is that the TemplateRef itself doesn't trigger change detection. Angular's change detection system relies on observable events, such as DOM events or property changes, to detect and propagate changes. Since a TemplateRef is a passive object without any observable events, changes to the TemplateRef itself might not trigger change detection.

To work around this issue, you can manually trigger change detection when the TemplateRef changes. Here's an example of how you can do that:

  1. Import the necessary dependencies in your component:

    typescript
    import { Component, Input, TemplateRef, ChangeDetectorRef } from '@angular/core';
  2. Inject the ChangeDetectorRef into your component's constructor:

    typescript
    constructor(private cdr: ChangeDetectorRef) {}
  3. Create an @Input property for the TemplateRef:

    typescript
    @Input() templateRef: TemplateRef<any>;
  4. Use the cdr.detectChanges() method to manually trigger change detection when the TemplateRef changes:

    typescript
    ngAfterContentInit() { // Detect changes initially this.cdr.detectChanges(); } ngOnChanges() { // Detect changes whenever the TemplateRef changes this.cdr.detectChanges(); }

By manually calling cdr.detectChanges(), you ensure that change detection is triggered and any changes in the TemplateRef are detected and propagated.

Remember to import the TemplateRef from @angular/core and not from @angular/common, as the latter won't provide the necessary change detection functionality.

If you're using @ContentChildren with a QueryList to query multiple TemplateRef instances, you can apply the same approach to each item in the QueryList to ensure changes are detected properly.

Please note that manually triggering change detection should be used judiciously, as it can have performance implications. It's generally recommended to let Angular's change detection system handle changes automatically whenever possible.

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