为了使不带复选框的多选下拉列表正常工作，我们需要通过使用ngModel和ngModelChange来实现选择的跟踪和更新。以下是一个示例代码：

HTML模板：

    
        
            {{fruit.viewValue}}
        
    

组件：

import { Component, OnInit } from '@angular/core';
import { FormControl } from '@angular/forms';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {
  fruits = [
    { value: 'apple', viewValue: 'Apple' },
    { value: 'orange', viewValue: 'Orange' },
    { value: 'banana', viewValue: 'Banana' },
    { value: 'grape', viewValue: 'Grape' }
  ];
  fruitSelect = new FormControl('');

  ngOnInit() {
    this.fruitSelect.valueChanges.subscribe(() => {
      const selectedFruits = this.fruits.filter(
        fruit => this.getFruitSelection(fruit.value)
      );
      console.log('Selected fruits:', selectedFruits);
    });
  }

  getFruitSelection(fruitValue: string) {
    return this.fruitSelect.value && this.fruitSelect.value.indexOf(fruitValue) > -1;
  }

  onDropdownOpened() {
    // Set the previous value of the select as the initial value when the dropdown is opened
    this.fruitSelect['_previousValue'] = this.fruitSelect.value;
  }

  onDropdownClosed() {
    // Revert to the previous value if empty input is submitted
    if (!this.fruitSelect.value || this.fruitSelect.value.length === 0) {
      this.fruitSelect.setValue(this.fruitSelect['_previousValue']);
    }
  }

}

在这个示例中，我们使用了mat-select