Binding 'this' in Angular Material Autocomplete displayWith using Angular 5

Question

I was trying to use the Material Angular autocomplete and I came across the displayWith function which can be apparently used to be the output that is displayed on selection. I wanted to call a custom function within the display function like

displayFn(id) {
 return this.getValue(id)
}
getValue(id) {
 /**return some string
}

For the autocomplete

<mat-autocomplete #autoOutlet="matAutocomplete" [displayWith]="displayFn">
  <mat-option *ngFor="let option of outletFilterOptions | async [value]="option.outletId">
   {{ option.outletName }}
  </mat-option>
</mat-autocomplete>

As you see I am using the id as the model instead of the entire object.

When the display function returned an error that this.getValue is undefined I searched Stack Overflow for a solution and was suggested that I use something like [displayWith]="displayFn.bind(this)".

But unfortunately, that isn't working for me either. I am using Angular material 5.1.0.

Is there something I am missing?

Answer 1

displayFn = value => {
  // now you have access to 'this' 
  this.someMethod();
  return 'formatted display';
}

Answer 2

It is because of this is not binding to the component and its binding to mat-select option

NOw for using component's function, you have to use arrow function, the preferable method or pass this from the HTML function

I will use the arrow function to use the component's function

Without arrow function

displayFn(data: any) {
    return data.Id?this.sometask(data):''
}

With arrow function

displayFn = (data: any) => {
    return data.Id?this.sometask(data):''
}

This work in my scenario and it worked in your scenario too.