md-autocomplete onSelectionChange 触发了两次

Question

我在 Angular 应用程序中使用 md-autocomplete angular/material: 2.0.0-beta.5。在最新版本中，selected方法已被 onSelectionChange 取代。

第一次从下拉列表中选择值

时，仅触发一次关联的方法，但是如果我从下拉列表中选择新值，则会选择两次(第二次具有前一个值(。

逻辑在以前的版本中正常工作。

模板

<md-autocomplete #panel="mdAutocomplete" [displayWith]="displayFn">
   <md-option (onSelectionChange)="selected(country)" *ngFor="let country of filteredCountries | async" [value]="country">
    <div class="selector-elements">
      <span>
          <img [src]="getFlagPath(country.code)" [width]="24" [height]="24" /> 
      </span>    {{ country.name }}
      </div>
</md-option>

控制器

export class CountrySelector implements OnInit, ControlValueAccessor {
// ...
initCountries() {
    this.countryList = countryNames;
    this.filteredCountries = this.formControlName.valueChanges
        .startWith(null)  //-> OnInit the countries are filtered by null, hence all results are returned.
        .map(country => {
            return country && typeof country === 'object' ? country.name : country
        })
        .map(name => name ? this.filter(name) : this.countryList.slice());
}
filter(val: string): ICountry[] {
    //Regex to match with the first letters of the country name with the passed value.
    return this.countryList.filter(country => new RegExp(`^${val}`, 'gi').test(country.name));
}
resetCountrySelection(){
    let country = new Country();
    this.formControlName.setValue(country);
    this.propagateChange(country);
}
writeValue(country: Country): void {
    if (country) {
        this.formControlName.setValue(country);
    }
}
selected(country: ICountry) {
   // Here it gets triggered twice when a new element is chosen
   this.propagateChange(country);
}
propagateChange = (_: any) => { };
registerOnChange(fn: any) {
    this.propagateChange = fn;
}
}

Answer 1

正在发生的事情是 onSelectionChange 按该顺序为新选择的和未选择的触发。 如果您像这样将$event添加到通话中

(onSelectionChange)="selected($event, country)"

然后，您可以通过像这样查看源来检查它是否是选定的一个

selected(event: MdOptionSelectionChange, country: ICountry) {
   if (event.source.selected) {
       this.propagateChange(country);
   }
}