Custom Angular 2 decorator designed for post-RC4 versions triggers the 'Multiple Components' exception

Question

Custom Angular 2 decorator designed for post-RC4 versions triggers the 'Multiple Components' exception

Currently, I am in the process of updating my Ionic 2 component known as ionic2-autocomplete. This component was initially created for RC.4 and earlier iterations, and now I am working on migrating it to Angular 2 final.

One key aspect of the original design is allowing developers to override the default template using a custom decorator called AutoCompleteItem, which can accept either template or templateUrl. The code for this decorator can be found here.

To maintain specific attributes required for the component while enabling users to customize its design, I made use of the decorator.

Following the steps outlined in the documentation, I attempted to implement a custom template by including:

import {AutoCompleteItem, AutoCompleteItemComponent} from 'ionic2-auto-complete';

@AutoCompleteItem({
  template : `<img src="build/images/flags/{{data.name}}.png" class="flag" /> <span [innerHTML]="data.name | boldprefix:keyword"></span>`,
})
export class CompTestItem extends AutoCompleteItemComponent{
}

This method worked flawlessly with the previous versions, where I also added CompTestItem to the declarations array.

However, I am now facing an exception that reads:

polyfills.js:3 Unhandled Promise rejection: Template parse errors: More than one component: AutoCompleteItemComponent, CompTestItem ("
[ERROR ->] ; Task: Promise.then ; Value: Error: Template parse errors:(…) Error: Template parse errors: More than one component: AutoCompleteItemComponent, CompTestItem ("
[ERROR ->]http://localhost:8101/build/main.js:19480:19) at RuntimeCompiler._compileTemplate (http://localhost:8101/build/main.js:27855:51) at http://localhost:8101/build/main.js:27777:83 at Set.forEach (native) at compile (http://localhost:8101/build/main.js:27777:47) at t.invoke (http://localhost:8101/build/polyfills.js:3:13400) at e.run (http://localhost:8101/build/polyfills.js:3:10787) at http://localhost:8101/build/polyfills.js:3:8889 at t.invokeTask (http://localhost:8101/build/polyfills.js:3:14029) at e.runTask (http://localhost:8101/build/polyfills.js:3:11389)o @ polyfills.js:3r @ polyfills.js:3i @ polyfills.js:3 polyfills.js:3 Error: Uncaught (in promise): Error: Template parse errors:(…)o @ polyfills.js:3r @ polyfills.js:3i @ polyfills.js:3

I am perplexed as to why this issue has arisen. Can anyone shed light on why this custom decorator is not functioning correctly on the current Angular version? And what could be causing the error message indicating multiple components?

Thank you!

angular typescript

Answer 1

Answer №1

Clarifying the points I made earlier, let's take a closer look at your decorator.

export function AutoCompleteItem( config: AutoCompleteItemMetadata ) {
  return function(cls: any) {
    const _reflect: any = Reflect;
    let annotations = _reflect.getMetadata('annotations', cls) || [];
    let extendedConfig: any = config;

    extendedConfig.selector = 'ion-auto-complete-item';
    annotations.push(new Component(extendedConfig));
    _reflect.defineMetadata('annotations', annotations, cls);

    return cls;
  };
}

The issue arises from setting the selector on every component to ion-auto-complete-item. In this scenario,

@AutoCompleteItem({
  template: defaultTemplate
})
export class AutoCompleteItemComponent {}

@AutoCompleteItem({})
export class ExtendedComponent extends AutoCompleteComponent {}

You now have two components sharing the same selector. While not problematic initially, Angular may struggle to decide which one to utilize when they are both present.

In prior versions like RC4, this was less of an issue due to confined scopes through the use of directives.

@Component({
  directives: [ AutoCompleteItemComponent ]
})
class SomeComponent {}

However, with modules introduced, the scope widens and potential conflicts increase.

Consider a shared module imported into another:

@NgModule({
  imports: [ FormsModule, CommonModule ],
  declarations: [ AutoCompleteItemComponent ],
  exports: [ AutoCompleteItemComponent ]
})
class SharedModule {}

@NgModule({
  imports: [ SharedModule ],
  declarations: [ ExtendedComponent, ComponentThatUsesExendedComponent ]
  exports: [ ComponentThatUsesExtendedComponent ]
})
class OtherModule {}

In this case, you'll encounter an error as both AutoComponentItemComponent and ExtendedComponent coexist within

ComponentThatUsesExendedComponent

.

More than one component AutoCompleteItemComponent, ExtendedComponent

To prevent such conflicts, ensure these components do not overlap in their usage. Keep in mind that each component class can only be declared in one module, adding further complexity to potential resolutions.

Answer 2

Clarifying the points I made earlier, let's take a closer look at your decorator.

export function AutoCompleteItem( config: AutoCompleteItemMetadata ) {
  return function(cls: any) {
    const _reflect: any = Reflect;
    let annotations = _reflect.getMetadata('annotations', cls) || [];
    let extendedConfig: any = config;

    extendedConfig.selector = 'ion-auto-complete-item';
    annotations.push(new Component(extendedConfig));
    _reflect.defineMetadata('annotations', annotations, cls);

    return cls;
  };
}

The issue arises from setting the selector on every component to ion-auto-complete-item. In this scenario,

@AutoCompleteItem({
  template: defaultTemplate
})
export class AutoCompleteItemComponent {}

@AutoCompleteItem({})
export class ExtendedComponent extends AutoCompleteComponent {}

You now have two components sharing the same selector. While not problematic initially, Angular may struggle to decide which one to utilize when they are both present.

In prior versions like RC4, this was less of an issue due to confined scopes through the use of directives.

@Component({
  directives: [ AutoCompleteItemComponent ]
})
class SomeComponent {}

However, with modules introduced, the scope widens and potential conflicts increase.

Consider a shared module imported into another:

@NgModule({
  imports: [ FormsModule, CommonModule ],
  declarations: [ AutoCompleteItemComponent ],
  exports: [ AutoCompleteItemComponent ]
})
class SharedModule {}

@NgModule({
  imports: [ SharedModule ],
  declarations: [ ExtendedComponent, ComponentThatUsesExendedComponent ]
  exports: [ ComponentThatUsesExtendedComponent ]
})
class OtherModule {}

In this case, you'll encounter an error as both AutoComponentItemComponent and ExtendedComponent coexist within

ComponentThatUsesExendedComponent

.

More than one component AutoCompleteItemComponent, ExtendedComponent

To prevent such conflicts, ensure these components do not overlap in their usage. Keep in mind that each component class can only be declared in one module, adding further complexity to potential resolutions.

Custom Angular 2 decorator designed for post-RC4 versions triggers the 'Multiple Components' exception

Answer №1

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