Can you specify a data type for ngFor in Angular?

I am currently employing ngFor to iterate over a collection of a specific type [Menu] within Angular 4.x.

During this process, I am looping through a collection property of the menu object (menu.items).

Unfortunately, my IDE (Eclipse + Angular IDE) is unable to recognize this property, even though the Menu class distinctly defines the items property as an array of MenuItem.

Is there a possible solution to this issue?

https://i.sstatic.net/fJHnN.png

The class declarations that are relevant include -

export class MenuBase {
  id: string;
  title: string;
  isPublic: boolean;
  roles: string[];
  items: MenuItem[];
  position: number;
// the rest of the class has been omitted
}

export class MenuItem extends MenuBase {
  menuItemType: MenuItemType;
  callback: () => void;
  location: string;

  constructor (options: any) {
    super(options);
    this.location = options.location;
    this.menuItemType = options.menuItemType || MenuItemType.location;
    this.callback = options.callback;
  }
}

export class Menu extends MenuBase {
  constructor (options: any) {
    super(options);
  }
}

Additional details

The project I was working on can be found at: https://github.com/savantly-net/ngx-menu. Even though it's valid, the project displays an error in Eclipse.

Although no documentation was created by me, I utilized it from here - https://github.com/savantly-net/sprout-platform/tree/master/web/sprout-web-ui

Answer №1

One method that I have found effective is to create a new component specifically for the template that utilizes the *ngFor directive for rendering and ensuring type safety.

Here is an example of how this can be implemented:

<ng-container *ngFor="let item of items" >
  <my-custom-component [item]="item"></my-custom-component>
</ng-container>

In the custom component template, you can handle different scenarios based on the item's menuItemType:

<div *ngIf="item.menuItemType == 'dropdown'">
  <!-- Code for dropdown scenario -->
</div>

<div *ngIf="item.menuItemType !== 'dropdown'">
  <!-- Handle other scenarios here -->
</div>

Additionally, in the TypeScript file for the custom component, ensure that the input property is correctly typed:

@Component({})
export class MyCustomComponent {
  @Input() item: MenuItem;
}

Answer №2

By the way, when working in Visual Studio Code, make sure to specify it in the appropriate tsconfig.json file:

"angularCompilerOptions": {
    "fullTemplateTypeCheck": true,
    "strictInputTypes": true,
}

Answer №3

A solution to this issue is using a pipe. Originally, the code was causing a type error:

<ng-container *ngIf="(item.value.value - defaultCssFilters[item.key].value) > 0">
  ...
</ng-container>

To resolve the problem, a pipe was implemented:

<ng-container *ngIf="(item.value.value - (defaultCssFilters | filterValue: item.key)) > 0">
  ...
</ng-container>

The custom pipe created for this purpose is as follows:

@Pipe({ name: 'filterValue' })
export class FilterValuePipe implements PipeTransform {
  transform(cssFilters: ICssFilters, key: TCssFilter): number {
    return cssFilters[key].value;
  }
}

This method is advantageous as it allows for the declaration of types within the pipe itself.

When dealing with existing code, utilizing a pipe is more convenient than generating a new component.

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