Create Html local variable programmatically with Angular2

问题

I need to know if there is a way to create HTML local variables programmatically.

I am developing a web app where I have an NgFor loop and I want to be able to assign a local variable to each sub element created by the NgFor.

ie :

<div *ngFor="#elt of eltList" >
    <span #setLocalVariable(elt.title)></span>
</div>

setLocalVariable(_title : string){
    let var = do some stuff to _title;
    return var;
}

The exemple above shows you what I am trying to accomplish and obviously does not work. Is there a way to achieve this ?

Thank you in advance.

Edit:

After seeing the answers I got (and i thank everyone who took the time to read my question and tried to answer it) i'll explain a bit more why i want it that way.

I will be using : loadIntoLocation() from the DynamicComponentLoader. That function got as a 3rd parameter a string that refers to an anchors (ie : #test in an html element). Thats why i need to create those local variables with a name equal to the one of my elt.title.

回答1:

I think local variables (defined with the # character) don't apply for your use case.

In fact, when you define a local variable on an HTML element it corresponds to the component if any. When there is no component on the element, the variable refers to the element itself.

Specifying a value for a local variable allows you to select a specific directive associated with the current element. For example:

<input #name="ngForm" ngControl="name" [(ngModel)]="company.name"/>

will set the instance of the ngForm directive associated with the current in the name variable.

So local variables don't target what you want, i.e. setting a value created for the current element of a loop.

If you try to do something like that:

<div *ngFor="#elt of eltList" >
  <span #localVariable="elt.title"></span>
  {{localVariable}}
</div>

You will have this following error:

Error: Template parse errors:
There is no directive with "exportAs" set to "elt.title" ("
  <div *ngFor="#elt of eltList" >
    <span [ERROR ->]#localVariable="elt.title"></span>
    {{localVariable}}
  </div>
"): AppComponent@2:10

Angular2 actually looks for a directive matching the provided name elt.title here)... See this plunkr to reproduce the error: https://plnkr.co/edit/qcMGr9FS7yQD8LbX18uY?p=preview

See this link: http://victorsavkin.com/post/119943127151/angular-2-template-syntax, section "Local variables" for more details.

In addition to the current element of the iteration, ngForm only provides a set of exported values that can be aliased to local variables: index, last, even and odd.

See this link: https://angular.io/docs/ts/latest/api/common/NgFor-directive.html

What you could do is to create a sub component to display elements in the loop. It will accept the current element as parameter and create your "local variable" as attribute of the component. You will be able then to use this attribute in the template of the component so it will be created once per element in the loop. Here is a sample:

@Component({
  selector: 'elt',
  template: `
    <div>{{attr}}</div>
  `
})
export class ElementComponent {
  @Input() element;

  constructor() {
    // Your old "localVariable"
    this.attr = createAttribute(element.title);
  }

  createAttribute(_title:string) {
    // Do some processing
    return somethingFromTitle;
  }
}

and the way to use it:

<div *ngFor="#elt of eltList" >
  <elt [element]="elt"></elt>
</div>

Edit

After your comment, I think that you try the approach described in this answer. Here are more details: create dynamic anchorName/Components with ComponentResolver and ngFor in Angular2.

Hope it helps you, Thierry

回答2:

You could stick it into the template interpolation since it handles expressions.

<div *ngFor="#elt of eltList" >
    <span>{{setLocalVariable(#elt)}}</span>
</div>

setLocalVariable(_title : string){
    let var = do some stuff to _title;
    return var;
}

来源：https://stackoverflow.com/questions/34877907/create-html-local-variable-programmatically-with-angular2

标签

html

angular

local-variables